Enhanced Structural and Magnetic Coupling in a Mesocrystal-Assisted

Subscriber access provided by FLORIDA INTL UNIV

Article

Enhanced structural and magnetic coupling in a mesocrystal-assisted nanocomposite Yuanmin Zhu, Qian Zhan, Jan-chi Yang, Yugandhar Bitla, Pingping Liu, ChenI Li, Heng-Jui Liu, V. Suresh Kumar, Elke Arenholz, Qing He, and Ying-Hao Chu ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.5b08026 • Publication Date (Web): 17 Nov 2015 Downloaded from http://pubs.acs.org on November 20, 2015

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

ACS Applied Materials & Interfaces is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 26

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Applied Materials & Interfaces

Enhanced structural and magnetic coupling in a mesocrystal-assisted nanocomposite Yuanmin Zhu1), Qian Zhan1)*, Jan-Chi Yang2), Yugandhar Bitla2), Pingping Liu1), Chen-I Li2), Heng-Jui Liu2), V. Suresh Kumar2), Elke Arenholz3), Qing He4) and Ying-Hao Chu2,5)* 1)

Department of Material Physics and Chemistry, University of Science and

Technology Beijing, Beijing 100083, China; 2) Department of Materials Science and Engineering, National Chiao Tung University, Hsinchu 30010, Taiwan; 3) Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA; 4) Department of Physics, Durham University, Durham DH1 3LE, United Kingdom; 5) Institute of Physics, Academia Sinica, Taipei 155, Taiwan ABSTRACT:

Benefitting from the advances made in well-controlled materials synthesis techniques, nanocomposites have drawn considerable attention due to their enthralling physics and

functionalities.

mesocrystal-perovskite

In

this

work,

we

nanocomposite,

report

a

new

heteroepitaxial

(NiFe2O4)0.33:(La0.67Ca0.33MnO3)0.67.

Elaborate structural studies revealed that tiny NiFe2O4 nanocrystals aggregate into ordered octahedral mesocrystal arrays with {111} facets together with a concomitant 1

ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 26

structural phase transition of the La0.67Ca0.33MnO3 matrix upon post-annealing process. Combined magnetic and x-ray absorption spectroscopic measurements show significant enhancement in the magnetic properties at room temperature due to the structural evolution of magnetic NiFe2O4 and the consequent magnetic coupling at the heterointerfaces

mediating

via

well connected

octahedrons

of Mn-O6

in

La0.67Ca0.33MnO3 and (Ni,Fe)-O6 in NiFe2O4. This work demonstrates an approach to manipulate the exciting physical properties of material systems by integrating desired functionalities of the constituents via synthesis of a self-assembled mesocrystal embedded nanocomposite system.

Keywords:

self-assembled

nanocomposite,

structural

evolution,

mesocrystal,

heterointerfaces, magnetic coupling INTRODUCTION Nanocomposite systems exhibiting intriguing physical properties and rich functionalities have attracted great attention in recent years owing to their potential applications for next-generation devices.1-3 Complex oxides nanocomposites exhibit a wide range of exciting functional properties, e.g., strongly enhanced current densities in the nanoparticles embedded YBa2Cu3O7–x+BaZrO3 films,4 thermally-stable high-κ response in perovskite nanosheets,5 thick lead-free ferroelectricity in BiFeO3-Sm2O36 and strong magnetoelectric coupling in BaTiO3-CoFe2O4 nanostructure7. Perovskite manganites, La(1-x)AxMnO3 (A=Ca, Sr, Ba, etc.), one of the classic functional complex 2


Page 3 of 26

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


oxides, have been investigated intensively due to their fascinating structural, magnetic and electronic properties such as the colossal magnetoresistance (CMR) effect.8-10 Moreover, non-magnetic insulators (e.g. SrTiO3, MgO, ZnO, CeO2, etc.), magnets (e.g. ZnFeO3, CuFe2O4, CoFe2O4, Mn3O4, etc.), ferroelectric (BaTiO3), and metals (Ag, Au) are used in composite systems as a tuning factor to modulate the physical properties of single phase manganites for the potential practical applications.2,11-18 The advance in thin film growth techniques has enabled the development of atomically flat hetero-interfaces and abundant varieties of oxide hetero-interfaces.19-23 More opportunities can be offered to manipulate the heterostructures and corresponding physical performance by introducing proper stress fields,24-26 various domain patterns,27

specific

chemical

bonding,28,29

etc.

For

example,

(La0.7Ca0.3MO3)1–x:(MgO)x nanocomposite system grown on MgO (100) substrate exhibits a very large CMR effect, which was attributed to a strain induced structural phase transition.26 The tunability of domain and grain boundary via structural modulation was achieved in (La0.7Sr0.3MnO3)0.7:(Mn3O4)0.3 nanocomposites.14 The evolution of the constituent phases in desired composite films can result in abundant hetero-interfaces with a variety of structural configurations accompanying with the interplays of stress field, chemical bonding, magnetic coupling, band alignment, etc.30-34 As a result, it is extremely interesting to see if one can create novel interfaces that can optimize or enhance the physical properties of the parent materials.

3



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 4 of 26

Driven by the aforementioned goal, we carried out the study of a mesocrystal embedded nanocomposite of (La0.67Ca0.33MnO3)0.67: (NiFe2O4)0.33 (LCMO:NFO) to examine the structural and magnetic coupling between two functional magnetic constituents. A thorough investigation of structural information and magnetic properties

established

that

the

magnetic

properties

of

the

hetroepitaxial

nanocomposite thin films are dictated by the structural evolution of NFO crystal modulating the interfacial coupling between the NFO mesocrystal and the LCMO matrix. Thus, the current study demonstrates how the morphology and microstructure of the nanocomposite thin films and in turn, their strain and material functionalities can be modulated via the structural evolution of self-assembled mesocrystals upon the post-annealing process.

EXPERIMENTAL SECTION Growth. The (La0.67Ca0.33MnO3)1-x: (NiFe2O4)x nanocomposites were epitaxially grown on SrTiO3(001) substrates by the pulsed laser deposition (PLD) technique at 750 ℃. By using a sequential dual-target deposition process, the molar ratios of the two phases were well controlled by adjusting the number of laser pulses striking each target. Series of nanocomposites with LCMO:NFO molar ratios of 4:1, 2:1 and 1:1 were synthesized. In the present work, the nanocomposite films with 2:1 (0.67:0.33) ratio was chosen as a model system, which is an optimized system with the best performance of magnetic properties. The actual molar ratio of the two phases was also 4


Page 5 of 26

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


estimated to be ~2:1 via X-ray reflectivity and scanning electron microscopy measurements based on single NFO and LCMO layers grown under the same growth condition. The as-grown thin films were subsequently annealed at an optimized temperature of 1100 ℃ for 12 hours in air to get better structure and performance. More growth details can be found in our related paper.35, 36 Characterization. The detailed microstructure of the films was investigated by transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) on TECNAI F20 and JOEL 2010. Cross-section and plane view TEM samples were prepared by the standard method: mechanical grinding, pre-thinning and low angle ion thinning process (Leica EM RES102, Germany). The magnetic properties were measured using magnetic property measurement system (MPMS, Quantum Design Co. Ltd). The X-ray absorption spectroscopy (XAS) spectra and photoemission electron microscopy (PEEM) were taken at Advanced Light Source, Lawrence Berkeley National Laboratory.

5



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 6 of 26

RESULTS AND DISCUSSION

Figure 1. Schematic and structural investigations of the (La0.67Ca0.33MnO3)0.67: (NiFe2O4)0.33 nanocomposite films. (a) Schematic of the LCMO-NFO nanocomposite system. (b) Bright field cross-sectional TEM images of an as-grown sample with the incident beam along [100] direction. The corresponding dark field image is shown in the inset at right-upper corner. Bottom inset shows the corresponding diffraction patterns. Subscripts “L”, “N” represent for LCMO, NFO phase, respectively. (c) Bright filed TEM images for post-annealed sample along [1-10] direction with the corresponding diffraction patterns shown in inset. (d) X-ray diffraction scans for the post-annealed LCMO-NFO nanocomposite film. (e) EDX spectra from the different points in each phase of the post-annealed sample.

First of all, it is crucial to establish the conceptual schematic and structural information of the LCMO-NFO nanocomposite, as illustrated in Figure 1(a), whereby the ferrimagnetic NFO mesocrystal was selected as a functional seeds to induce extrinsic coupling with ferromagnetic LCMO matrix. In the bulk, LCMO has an orthorhombic

distorted

perovskite

structure

(S.G.

Pnma

62)

with

a

ferromagnetic-paramagnetic phase transition at 250 K 37 while the ferrimagnetic NFO has an inverse spinel structure (S.G. Fd-3m 227) with a ferromagnetic-paramagnetic phase transition at 860 K.38,39 Figure 1(b)-(e) shows the structure and chemical 6


Page 7 of 26

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


composition of the as-grown and post-annealed samples. As-grown nanocomposite with vertically aligned nanocrystals and a flat surface on the STO substrate was observed in the cross-sectional transmission electron microscopy (TEM) image of the as-grown sample (Figure 1(b)). The NFO and LCMO phases show good epitaxy as resolved from the corresponding selected area electron diffraction patterns (EDPs): NFO[100](040) || LCMO[100](020)c (bottom inset in Figure 1(b)). A typical dark field image using the NFO (040) diffraction spot is given in the upper inset of Figure 1(b), depicting nanorod-like NFO nanocrystals with bright contrasts vertically aligned in LCMO matrix. After 12 hours post-annealing process at 1100 ℃, a significant change occurred in the film configuration, as shown in Figure 1(c). NFO phase exhibits recognizable larger mesocrystals with octahedron shape dispersed in the LCMO matrix and displays a reverse pyramid feature at the film surface, which is the equilibrium shape of spinels characterized by low-energy {111} surfaces.40 A cube-on-cube epitaxial orientation relationship is obtained with NFO(001)(111) || LCMO(001)(111)c revealed by the corresponding EDP shown as the inset. Consistent with these observations, the LCMO (00l)- and NFO (00l)-oriented peaks are clearly observed in the x-ray scan of LCMO-NFO nanocomposites (Figure 1(d)), suggesting a highly degree of phase separation. The reciprocal space maps (RSM) of the as-grown and post-annealed nanocomposites were also carried out shown in the Figure S1 (see the supplementary material). The chemical composition of LCMO

7



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 8 of 26

matrix and NFO mesocrystal was investigated based on the analysis of energy dispersive x-ray spectroscopy (EDX) in Figure 1(e). We found that about 15% of Mn3+ ions has substituted for Fe3+ ions in the NFO mesocrystal while equal amount of Fe3+ ions moves into the LCMO matrix correspondingly (see the quantification result of the EDX spectrums in Table S1). Inter-diffusion between Mn3+ and Ni2+ ions is rarely seen, which is expectable since whole nanocomposite system needs to maintain charge neutrality.

Figure 2. Plane-view TEM morphologies of LCMO-NFO composite films for (a) the as-grown sample and (b) the post-annealed sample with the NFO size histograms in the insets. The SEM image as inset in (b) shows the surface morphology of the nanocomposite. Corresponding EDPs of (c) as-grown and (d) post-annealed samples along with simulation results for the R-3c and Pnma structures of LCMO using JEMS in the insets. The subscripts,

pc, R, O,

represent pseudo-cubic,

rhombohedral and orthorhombic structure of the perovskite LCMO, respectively. Schematic illustrations of the structural evolution of LCMO-NFO in (e) as-grown and (f) post-annealed nanocomposite thin film.

8


Page 9 of 26

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


The surface morphology and microstructure of LCMO-NFO nanocomposites in both as-grown and post-annealed state have been investigated systematically in the plan-view direction. Figure 2(a) gives the dark-field image of the as-grown film by imaging NFO (040) diffraction spot, revealing fine NFO nanocrystals with an average lateral size of ~3 nm (inset). During the annealing process, NFO nanocrystals coalesce to form bigger ordered octahedral-shaped mesocrystals with an average size of ~16 nm (inset), which are uniformly distributed in the LCMO matrix, as shown in Figure 2(b). The scanning electron microscopy (SEM) image in the upper-corner inset also displays the morphology at the film surface. The corresponding EDPs from plane-view are given in Figs 2(c) and (d) for as-grown and post-annealed samples, respectively. A significant structural evolution occurred when the nanocomposite films underwent the post annealing process. Although bulk LCMO is an orthorhombic distorted perovskite structure, it shows a pseudo-cubic character in the as-grown sample [blue box in Figure 2(c)] with lack of the specific diffraction spots of orthorhombic structure. It was reported that LCMO would transform into rhombohedral structure (i.e. R-3c space group) due to the strain effects.41,

42

The

corresponding simulated EDP (bottom inset in Figure 2(c)) using the rhombohedral structure with R-3c space group for LCMO phase in the [241]R/[001]PC direction is consistent with our experimental result. On the other hand, three different orientation variants of orthorhombic LCMO are indexed in the post-annealed sample in Figure

9



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

2(d), as indicated by three blue boxes, exhibiting the specific (101)o, (10-1)o and (010)o superposition spots of Pnma orthorhombic structure. A corresponding simulated EDP (bottom inset in Figure 2d) using the orthorhombic structure with Pnma space group is in good agreement with the experimental image. Therefore, the annealing process transforms vertically aligned fine NFO nanocrystals with similar size and shape into a larger octahedral mesocrystal composed of a number of crystallographically oriented nanocrystals embedded in the LCMO matrix as illustrated in the schematic models of Figure 2(e) and (f), respectively.

Figure 3. (a) Cross-sectional HRTEM images with incident beam along [100] direction of as-grown sample shows the vertical aligned nano-sized NFO nanocrystals. The corresponding FFT pattern is shown in the inset. (b) Enlargement of selected area in (a) showing LCMO-NFO two-phase boundary. “L”, “N” represent for LCMO, NFO phase, respectively. Cross-sectional HRTEM microstructures of NFO mesocrystals with LCMO matrix along [1-10] direction for the post annealed sample: (c) floated at film surface and (d) embedded in the films. (e) IFFT (Inverse Fast Fourier Transform) of enlarged LCMO-NFO {111} interfaces in marked area of (d). (f) Statistical lattice measurements of the as-grown (black) and the post-annealed (red) LCMO-NFO samples. The corresponding bulk values are given as dotted lines.

10


Page 10 of 26

Page 11 of 26

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


In such a nanocomposite, a huge interface-to-volume ratio of the two constituents is achieved resulting in a large and more effective interfacial coupling unlike that found in lamellar heterostructures. However, well-defined interfaces between the constituents LCMO-NFO and their mismatch strain are highly desired for tailoring the intended functionalities of such nanostructure. A detailed high resolution TEM (HRTEM) study of the interface between LCMO matrix and NFO phase was performed. For the as-grown sample, vertically aligned NFO nanocrystals with the lateral size of ~3 nm were observed in the cross-sectional HRTEM image of Figure 3(a) (yellow dashed oval area). The corresponding fast Fourier transform (FFT) patterns shown in the inset reveals clear phase-separation of the two phases. Figure 3(b) is an enlarged view of the selected interface area in Figure 3(a) showing a clear LCMO-NFO interface lies in {100} plane. After the post-annealing process, bigger mesocrystals with reverse pyramid morphology were formed at the film surface with (001) as their surface and (111) facets conjuncting with LCMO matrix, as shown in Figure 3(c) along [1-10] direction. Meanwhile, NFO embedded in the matrix exhibited an octahedron shape with {111} heterointerfaces bonding with LCMO (Figure 3(d)), in which the structural continuity and uniform hetero-interface are well demonstrated by the connection of Mn-O6 in LCMO and (Ni,Fe)-O6 in NFO. As discussed above, both the crystal structure of LCMO matrix and the configuration of nanocrystalline NFO changed with sample processing conditions. To

11



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

reveal the lattice mismatch thus the strain state at the heterointerfaces, one-dimensional IFFT was performed on LCMO(111)c/NFO(111) spots for the yellow squared area in Figure 3(d), as shown in Figure 3(e). An extra LCMO(111)c plane can be observed at the heterointerface every ~11 planes, revealing a nominal lattice mismatch of ~9%. This is in good agreement with the calculated lattice mismatch (~8.5%) between LCMO and NFO bulk values,37, 38 indicating a nearly full lattice mismatch relaxation for both phases. However, the HRTEM of heterointerfaces in the as-grown films are almost coherent with no obvious edge dislocations, suggesting a strained state at the interface (the corresponding IFFT image is shown in Figure S3). Quantitative analysis of the local strain state near the two-phase interfaces in the composite films has been conducted through statistical local area lattice measurements of cross-sectional HRTEM images for both samples, as shown in Figure 3f. The bulk values are given in the plot as the dotted lines for reference. Within the experimental errors, the relative variations of the lattice parameters can reveal the complex strain states in the nanocomposite film system as discussed in other related works.43,44 For the as-grown films shown as in Figure 3f, out-of-plane lattice parameters of NFO(002) plane are suppressed compared to the in-plane lattice, indicating an out-of-plane compressive strain on NFO. On the contrary, the lattices of LCMO matrix experienced an out-of-plane tensile strain. For the post annealed sample, as shown in red circles, no significant difference is observed between the

12


Page 12 of 26

Page 13 of 26

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


in-plane and out-of-plane lattice parameters for both phases and the values are close to the bulk ones (marked as dotted lines) suggesting the stress relaxation upon annealing. In addition, high-resolution reciprocal space maps were carried out offering macroscopic lattice variation in the nanocomposites [Figure S1], which once again, confirms the strained and relaxed crystals in as-grown and post-annealed nanocomposites, respectively. Thus, the annealing process offers us an opportunity to manipulate the microstructures and optimize material properties in the nanocomposite system as demonstrated in the following sections. Strong correlations between the magnetic properties and strain state have been reported in some typical ferrites.45, 46 Therefore, different strain states in the magnetic phases should be taken into consideration when investigating the magnetic properties of the nanocomposites.

Figure 4. Magnetism and local electronic structure of LCMO-NFO nanocomposite. (a) Comparative temperature dependence of magnetization at H = 1 kOe for as-grown and post-annealed systems. (b) In-plane (IP) magnetic hysteresis loops at various temperatures. Room temperature XAS and XMCD spectra for the post-annealed sample with respect to (c) Fe L2,3, (d)

13



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 14 of 26

Ni L2,3 and (e) Mn L2,3 edges. (f) XMCD of Ni, Mn elements as a function of magnetic field. The Ni2+, Mn3+ ions exhibit parallel spin moments, revealing the coherent magnetic coupling in the LCMO-NFO nanocomposites.

With a well-established understanding of the microstructure, we further investigated the magnetic order and the coupling between the mesocrystal and the matrix. The thermal variation of magnetization at a static field of 1 kOe for both as-grown and post-annealed nanocomposite systems in ‘zero-field-cooled’ (ZFC) and ‘field-cooled’ (FC) modes presented in Figure 4(a) clearly marks the following inferences. 1. The magnetization of the post-annealed system is enhanced by an order of magnitude compared to the as-grown sample. 2. The bifurcation between ZFC-FC magnetization of as-grown exhibits typical features of superparamagnetic system while the post-annealed system has higher bifurcation temperature and the magnetic order-disorder transition temperature is rather sharp. The temperature dependence of magnetization for pure as-grown and annealed LCMO films shows negligible magnetization at room temperature (see the supplementary material Figure S4). The magnetic response is dominantly determined by the magnetic ordering of NFO, LCMO and LCMO-NFO hetero-interfaces (interfacial coupling). In fact, M(T) data in Figure 4(a) directly reflects the magnetic response and magnetic coupling between smaller

superparamagnetic

NFO

nanocrystals

(larger

single

domain

NFO

mesocrystal) and the underlying rhombohedral (orthorhombic) LCMO matrix in the as-grown (post-annealed) samples. The magnetic response gets suppressed in the former while enhanced in the latter case. The average crystallite sizes of NFO in 14


Page 15 of 26

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


as-grown and post-annealed nanocomposites are consistent with those reported for superparamagnetic and magnetic single domain NFO crystals.47-49 The hysteresis loops measured at various temperatures for LCMO-NFO composite systems is shown in Figure 4b. It can be observed that the post-annealed sample has higher magnetization and large coercive fields compared to the as-grown system. The coercive field decreases linearly with temperature as depicted in the inset. It is clear from the hysteresis loop at 280 K that the saturation magnetization is ~1.7 times higher and the coercive field is ~5 times larger for the post-annealed sample than the as-grown sample. The saturation magnetization at 4 K and 5 T (near the ground state) yielded a moment of 2.47 µB/f.u. and 1.2 µB/f.u. for the post-annealed and as-grown samples, respectively, as against the expected 3.12 µB/f.u. for (LCMO)0.67(NFO)0.33 formula. Thus, post-annealing process provides us an additional degree of freedom to tailor the functionality of mesocrystal embedded nanocomposites. Furthermore, we exploit the extreme sensitivity of x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) techniques to the local electronic structure to gain further insights about the nature of magnetic coupling in LCMO-NFO system. Figure 4c-4e shows the XAS and XMCD spectra of Fe, Mn and Ni across the L-edges of the annealed sample, which are the typical elements contributing the magnetic orders in LCMO matrix and NFO mesocrystals. The XMCD measurement of Fe3+ (Figure 4c) reveals spectrum that is consistent with

15



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

typical inverse spinel configuration wherein the Fe3+ ions occupy octahedral and tetrahedral sites equally. The magnetic moments of Fe3+at the octahedral and tetrahedral sites are anti-parallel and cancel out in NFO. As a result, for NFO mesocrystal, the net magnetic moment contributed from Fe3+ is negligible, while Ni2+ contributes to the net ferromagnetic order. As shown the absorption spectra in Figure 4d, the valence state of Mn indicate a combination of Mn3+, Mn4+ in accordance with La0.673+Ca0.332+Mn0.673+Mn0.334+O32- formula and Mn2+ due to the exposure of high-intensity x-ray while taking XAS measurements. The XMCD spectra of Figure 4d and 4e indicates a parallel alignment of the Ni and Mn moments suggesting a ferromagnetic coupling between the spins of the NFO mesocrystals and LCMO matrix. Additionally, a close examination of XMCD M-H loops of Ni and Mn shown in Figure 4f exhibiting the same coercivity, again confirms strong ferromagnetic coupling between NFO mesocrystals and LCMO matrix. It is noteworthy to observe an appreciable magnetic moment on manganese ion (Figure 4d) even at the room temperature when accompanied with NFO mesocrystal. This result is due to the spin-polarized Mn ions near the LCMO-NFO heterointerfaces by the NFO single domain with higher transition temperature. Therefore, new structural configuration based on mesocrystal-matrix system with different functional materials offers an alternative route to enhance the functionalities of the composite systems.

16


Page 16 of 26

Page 17 of 26

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 5. (a) Topography image of LCMO-NFO probed by photoemission electron microscopy

(PEEM), where the dark and bright contrasts stand for the NFO mesocrystal and LCMO matrix, respectively. The XMCD−PEEM images of (b) Ni2+ and (d) Mn3+, respectively. (c) and (e) are overlapped images of topography (a) and XMCD−PEEM image of Ni2+ (b), Mn3+ (d), respectively. The insets in Figure 5a and 5d-e show the enlarged selected area demonstrating the magnetic coupling at the heterointerfaces around the NFO mesocrystals in the same area. (f) Schematic illustrating the structural coupling at the 111-type hetero-interface along the [1-10] projection showing the connection of Mn-O6 and (Ni,Fe)-O6 octahedron with interdiffusion.

Having unveiled the nature of magnetic coupling between the embedded NFO mesocrystals and LCMO matrix by the aforementioned XAS and XMCD analysis, XMCD−photoemission electron microscopy (XMCD-PEEM) study was carried out to further investigate the local magnetic environment in the vicinity of the LCMO-NFO heterointerfaces. Figure 5a shows the topography image taken by PEEM, in which the dark and bright contrasts represent the mesocrystal and the matrix of post-annealed nanocomposite, respectively. The XMCD−PEEM image of Ni2+ and Mn3+ is displayed in Figures 5b and 5d, respectively, in which the areas with the darkest contrast give 17



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

largest XMCD signal. By overlapping the topography and Ni XMCD-PEEM image (in Figure 5c), it suggests that Ni can only be found in the mesocrystals and with spin aligned in the same direction. However, it is worth to note that the area giving strong XMCD contrast (dark) in the Mn XMCD-PEEM image (Figure 5d) forms the shapes that are very similar to the mesocrystals. In the overlapped the topography and Mn XMCD-PEEM images (Figure 5e), the magnetic area (showing dark XMCD contrast) in the Mn XMCD-PEEM image is slightly larger than the size of the mesocrystals, as indicated in the enlarged areas (insets) in Figure 5a, 5d and 5e. This suggests that the Mn ions in the LCMO matrix in the vicinity of LCMO-NFO heterointerfaces are magnetized, conclusively demonstrates that the magnetic coupling originate near the heterointerface. Moreover, the dark contrasts of Mn and Ni XMCD-PEEM images suggest that the magnetization of Mn and Ni are orientated in the same direction, implying an interfacial ferromagnetic coupling in accordance with the magnetic and XMCD M-H loops. Based on the results presented so far, a schematic of the structural correlation, inter-diffusion and magnetic coupling at the LCMO-NFO {111} heterointerface is illustrated in Figure 5f. The micro-structural evolution of NFO-LCMO nanocomposite resulting in enhanced magnetic moment of the composite system upon post-annealing can be understood in terms of the following scenario. The as-grown composited system consists of superparamagnetic spinel NFO nanocrystals embedded in ferromagnetic

18


Page 18 of 26

Page 19 of 26

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


rhombohedral LCMO matrix. NFO nanocrystal in superparamagnetic state doesn’t show a net magnetic moment at zero external magnetic field due to randomly blocked spin moments, in turn suppresses the magnetic response of the as-prepared nanocomposite via interfacial coupling. On the other hand upon post-annealing, NFO nanocrystals coalesce to form a single domain with a larger moment enclosed by (111) facets with a simultaneous rhombohedral-orthorhombic (un-strained) structural transition of the LCMO matrix relaxing the surrounding constrain. Strong interfacial ferromagnetic coupling between well connected (Ni,Fe)O6 and MnO6 octahedra (Figure 5(f)), further, enhances the magnetic response of the system. CONCLUSION In summary, we have fabricated a self-assembled nanocomposite system, in which small NFO nanocrystals in the superparamagnetic limit are embedded in the ferromagnetic LCMO matrix transform into a bigger octahedral mesocrystals having magnetic single domain size enclosed by {111} facets accompanied with structural phase transition of LCMO matrix upon post-annealing. Significant enhancement in magnetic properties of the created nanocomposite at the room temperature is a consequence of the magnetic coupling at the {111} heterointerfaces. Larger yet more effective hetero-interface coupling inherent in the mesocrystal-embedded composite, demonstrated in the prototype LCMO-NFO system, paves an efficient route to improve the performance of nanocomposite systems by combining diverse

19



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

functionalities of the constituents. The enhanced properties and tunable features of the mesocrystal-embedded nanocomposites not only offers diverse physics but also facilitates a novel design and development of functional nanocomposites for next generation nanoelectronics.

ASSOCIATED CONTENTS Supporting Information

High-resolution reciprocal space maps of the samples Figure S1; XRD scans of samples Figure S2; Quantitative analysis of the EDX Table S1; HRTEM interface analysis for as-grown sample Figure S3; M-T data for pure LCMO films Figure S4. The Supporting Information is available free of charge on the ACS Publications website at xxxx.

Author information Corresponding author

*Address corresponding to E-mail: Prof. Q.Zhan: [email protected]; Prof. Y.H.Chu: [email protected] Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript.

20


Page 20 of 26

Page 21 of 26

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Notes The authors declare no competing financial interest.

ACKNOWLEDGEMENTS

This work is supported by National Natural Science Foundation of China with Grant Nos. 51371031 and 51571021. The authors in National Chiao Tung University are supported by Ministry of Science and Technology, Taiwan (grant MOST 103-2119-M-009-003-MY3); by the Ministry of Education, Republic of China (grant MOE-ATU 101W961); and by the Center for Interdisciplinary Science at National Chiao Tung University, Republic of China.

REFERENCES (1) Lee, O.; Harrington, S. A.; Kursumovic, A.; Defay, E.; Wang, H.; Bi, Z.; Tsai, C. F.; Yan, L.; Jia, Q.; Macmanus-Driscoll, J. L. Extremely High Tunability and Low Loss in Nanoscaffold Ferroelectric Films. Nano Lett. 2012, 12, 4311-4317. (2) Staruch, M.; Gao, H.; Gao, P.-X.; Jain, M. Low-Field Magnetoresistance in La0.67Sr0.33MnO3:ZnO Composite Film. Adv. Funct. Mater. 2012, 22, 3591-3595. (3) Tettey, K. E.; Yee, M. Q.; Lee, D. Photocatalytic and Conductive MWCNT/TiO2 Nanocomposite Thin Films. ACS Appl. Mater. Interfaces 2010, 2, 2646-2652. (4) MacManus-Driscoll, J.; Foltyn, S.; Jia, Q.; Wang, H.; Serquis, A.; Civale, L.; Maiorov, B.; Hawley, M.; Maley, M.; Peterson, D., Strongly Enhanced Current Densities in Superconducting Coated Conductors of YBa2Cu3O7–x+BaZrO3. Nat. Mater. 2004, 3 (7), 439-443. (5) Kim, Y.-H.; Kim, H.-J.; Osada, M.; Li, B.-W.; Ebina, Y.; Sasaki, T., 2d Perovskite Nanosheets with Thermally-Stable High-κ Response: A New Platform for High-Temperature Capacitors. ACS Appl. Mater. Interfaces 2014, 6 (22), 19510-19514. 21



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(6) Harrington, S. A.; Zhai, J.; Denev, S.; Gopalan, V.; Wang, H.; Bi, Z.; Redfern, S. A. T.; Baek, S. H.; Bark, C. W.; Eom, C. B., Thick Lead-Free Ferroelectric Films with High Curie Temperatures through Nanocomposite-Induced Strain. Nat. Nanotechnol. 2011, 6 (8), 491-495. (7) Zheng, H; Wang, J; Loﬂand, S. A.; Ma, Z.; Mohaddes-Ardabili, L; Zhao, T.; Salamanca-Riba, L.; Shinde, S. R.; Ogale, S. B.; Bai, F.; Viehland, D; Jia, Y.; Schlom, D. G.; Wuttig, M; Roytburd;, A.; Ramesh, R., Multiferroic BaTiO3-CoFe2O4 Nanostructures. Science 2004, 303 (30), 661-663. (8) Millis, A.; Shraiman, B. I.; Mueller, R. Dynamic Jahn-Teller Effect and Colossal Magnetoresistance in La1-x Srx MnO3. Phys. Rev. Lett. 1996, 77, 175-178. (9) Helmolt, R. von; Wecker, J.; Holzapfel, B.; Schultz, L.; Samwer, K. Giant Negative Magnetoresistance in Perovskitelike La2/3 Ba1/3 MnOx Ferromagnetic Films. Phys. Rev. Lett. 1993, 71, 2331-2333. (10) Chahara, K.; Ohno, T.; Kasai, M.; Kozono, Y. Magnetoresistance in Magnetic Manganese Oxide with Intrinsic Antiferromagnetic Spin Structure. Appl. Phys. Lett. 1993, 63, 1990-1992. (11) Keshri, S.; Joshi, L.; Rajput, S. S. Studies on La0.67Ca0.33MnO3–SrTiO3 Composites Using Two-Phase Model. J. Alloys Compd. 2011, 509, 5796-5803. (12) Staruch, M.; Cantoni, C.; Jain, M. Systematic Study of Magnetotransport Properties and Enhanced Low-Field Magnetoresistance in Thin Films of La0.67Sr0.33MnO3 + Mg(O). Appl. Phys. Lett. 2013, 102, 062416. (13) Tian, Z. M.; Yuan, S. L.; Wang, Y. Q.; Liu, L.; Yin, S. Y.; Li, P.; Liu, K. L.; He, J. H.; Li, J. Q. Electrical Transport and Magnetic Properties in La0.67Ca0.33MnO3 and CuFe2O4 Composites. Mater. Sci. Eng., B 2008, 150, 50-54. (14) Bi, Z.; Weal, E.; Luo, H.; Chen, A.; MacManus-Driscoll, J. L.; Jia, Q.; Wang, H. Microstructural and Magnetic Properties of (La0.7Sr0.3MnO3)0.7:(Mn3O4)0.3 Nanocomposite Thin Films. J. Appl. Phys. 2011, 109, 054302. (15) Bose, E.; Taran, S.; Karmakar, S.; Chaudhuri, B. K.; Pal, S.; Sun, C. P.; Yang, H. D. Effect of Grain Boundary Layer Strain on The Magnetic and Transport Properties of (100−x) La0.7Ca0.3MnO3/(x) BaTiO3 Composites Showing Enhanced Magnetoresistance. J. Magn. Magn. Mater. 2007, 314, 30-36. (16) Young, S.; Chen, H.; Lin, C.; Shi, J.; Horng, L.; Shih, Y.-T. Magnetotransport Properties of (La 0.7Pb0.3 MnO3)1− x/Agx Composites. J. Magn. Magn. Mater. 2006, 303, e325-e328.

22


Page 22 of 26

Page 23 of 26

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(17) Balcells, L.; Carrillo, A.; Martinez, B.; Fontcuberta, J., Enhanced Field Sensitivity Close to Percolation in Magnetoresistive La2/3Sr1/3MnO3/CeO2 Composites. Appl. Phys. Lett. 1999, 74 (26), 4014-4016. (18) Yan, C. H.; Xu, Z. G.; Zhu, T.; Wang, Z. M.; Cheng, F. X.; Huang, Y. H.; Liao, C. S., A Large Low Field Colossal Magnetoresistance in the La0.7Sr0.3MnO3 and CoFe2O4 Combined System. J. Appl. Phys. 2000, 87 (9), 5588-5590. (19) Schlom, D. G.; Chen, L.-Q.; Pan, X.; Schmehl, A.; Zurbuchen, M. A. A Thin Film Approach to Engineering Functionality into Oxides. J. Am. Ceram. Soc. 2008, 91, 2429-2454. (20) Hwang, H.; Iwasa, Y.; Kawasaki, M.; Keimer, B.; Nagaosa, N.; Tokura, Y. Emergent Phenomena at Oxide Interfaces. Nat. Mater. 2012, 11, 103-113. (21) Mannhart, J.; Schlom, D. G. Oxide Interfaces--an Opportunity for Electronics. Science 2010, 327, 1607-1611. (22) Yu, P.; Luo, W.; Yi, D.; Zhang, J.; Rossell, M.; Yang, C. H.; You, L.; Singh-Bhalla, G.; Yang, S.; He, Q. Interface Control of Bulk Ferroelectric Polarization. Proc. Natl. Acad. Sci. U.S.A. 2012, 109, 9710-9715. (23) Hsieh, Y. H.; Liou, J. M.; Huang, B. C.; Liang, C. W.; He, Q.; Zhan, Q.; Chiu, Y. P.; Chen, Y. C.; Chu, Y. H. Local Conduction at the BiFeO3 -CoFe2O4 Tubular Oxide Interface. Adv. Mater. 2012, 24, 4564-4568. (24) Mukherjee, A.; Cole, W. S.; Woodward, P.; Randeria, M.; Trivedi, N. Theory of Strain-Controlled Magnetotransport and Stabilization of the Ferromagnetic Insulating Phase in Manganite Thin Films. Phys. Rev. Lett. 2013, 110, 157201. (25) Zhu, Y. M.; Liu, P.; Yu, R.; Hsieh, Y.-H.; Ke, D.; Chu, Y.-H.; Zhan, Q. Orientation-tuning in Self-assembled Heterostructures Induced by a Buffer Layer. Nanoscale 2014, 6, 5126-5131. (26) Moshnyaga, V.; Damaschke, B.; Shapoval, O.; Belenchuk, A.; Faupel, J.; Lebedev, O. I.; Verbeeck, J.; van Tendeloo, G.; Mucksch, M.; Tsurkan, V.; Tidecks, R.; Samwer, K. Structural Phase Transition at the Percolation Threshold in Epitaxial (La0.7Ca0.3MnO3)1-x:(MgO)x Nanocomposite Films. Nat. Mater. 2003, 2, 247-252. (27) Zhu, Y. M.; Ke, D.; Yu, R.; Hsieh, Y. H.; Liu, H. J.; Liu, P. P.; Chu, Y. H.; Zhan, Q. Self-Assembled Perovskite-Spinel Heterostructure on a Highly Distorted Substrate. Appl. Phys. Lett. 2013, 102, 111903. (28) Zhan, Q.; Yu, R.; Crane, S. P.; Zheng, H.; Kisielowski, C.; Ramesh, R. Structure and Interface Chemistry of Perovskite-Spinel Nanocomposite Thin Films. Appl. Phys. Lett. 2006, 89, 172902. 23



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(29) Liang, W. I.; Liu, Y. M.; Liao, S. C.; Wang, W. C.; Liu, H. J.; Lin, H. J.; Chen, C. T.; Lai, C. H.; Borisevich, A.; Arenholz, E.; Li, J.; Chu, Y. H. Design of Magnetoelectric Coupling in a Self-Assembled Epitaxial Nanocomposite via Chemical Interaction. J. Mater. Chem. C 2014, 2, 811-815. (30) Yu, P.; Chu, Y.-H.; Ramesh, R. Oxide Interfaces: Pathways to Novel Phenomena. Mater. Today 2012, 15, 320-327. (31) Jia, C.; Berakdar, J. Thermoelectric Effect of Multiferroic Oxide Interfaces. Appl. Phys. Lett. 2011, 98, 042110. (32) Chen, A.; Bi, Z.; Tsai, C.-F.; Lee, J.; Su, Q.; Zhang, X.; Jia, Q.; MacManus-Driscoll, J. L.; Wang, H. Tunable Low-Field Magnetoresistance in (La0.7Sr0.3MnO3)0.5:(ZnO)0.5 Self-Assembled Vertically Aligned Nanocomposite Thin Films. Adv. Funct. Mater. 2011, 21, 2423-2429. (33) Ohtomo, A.; Hwang, H. A High-mobility Electron Gas at the LaAlO3/SrTiO3 Heterointerface. Nature 2004, 427, 423-426. (34) Chen, A.; Bi, Z.; Jia, Q.; MacManus-Driscoll, J. L.; Wang, H., Microstructure, Vertical Strain Control and Tunable Functionalities in Self-Assembled, Vertically Aligned Nanocomposite Thin Films. Acta Mater. 2013, 61 (8), 2783-2792. (35) Liu, H. J.; Chen, L. Y.; He, Q.; Liang, C. W.; Chen, Y. Z.; Chien, Y. S.; Hsieh, Y. H.; Lin, S. J.; Arenholz, E.; Luo, C. W.; Chueh, Y. L.; Chen, Y. C.; Chu, Y. H. Epitaxial Photostriction-Magnetostriction Coupled Self-Assembled Nanostructures. ACS Nano 2012, 6, 6952-6959. (36) Yang, J.-C.; He, Q.; Zhu, Y.-M.; Lin, J.-C.; Liu, H.-J.; Hsieh, Y.-H.; Wu, P.-C.; Chen, Y.-L.; Lee, S.-F.; Chin, Y.-Y. Magnetic Mesocrystal-Assisted Magnetoresistance in Manganite. Nano Lett. 2014, 14, 6073-6079 (37) Blasco, J.; Garcia, J.; De Teresa, J.; Ibarra, M.; Algarabel, P.; Marquina, C. A Systematic Study of Structural, Magnetic and Electrical Properties of (La1-xTbx)2/3Ca1/3MnO3 Perovskites. J. Phys.: Condens. Matter 1996, 8, 7427-7442. (38) Subramanyam, K. Neutron and X-ray Diffraction Studies of Certain Doped Nickel Ferrites. J. Phys. C: Solid State Phys. 1971, 4, 2266-2268. (39) Komatsu, T.; Soga, N.; Kunugi, M., ESR Study of NiFe2O4 Precipitation Process from Silicate Glasses. J. Appl. Phys. 1979, 50 (10), 6469-6474. (40) Zheng, H.; Zhan, Q.; Zavaliche, F.; Sherburne, M.; Straub, F.; Cruz, M. P.; Chen, L. Q.; Dahmen, U.; Ramesh, R. Controlling Self-Assembled Perovskite-Spinel Nanostructures. Nano Lett. 2006, 6, 1401-1407.

24


Page 24 of 26

Page 25 of 26

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(41) Lebedev, O.; Verbeeck, J.; Van Tendeloo, G.; Shapoval, O.; Belenchuk, A.; Moshnyaga, V.; Damashcke, B.; Samwer, K. Structural Phase Transitions and Stress Accommodation in (La0.67Ca0.33MnO3)1-x:(MgO)x Composite Films. Phys. Rev. B 2002, 66, 104421. (42) Yang, H.; Cao, Z.; Shen, X.; Xian, T.; Feng, W.; Jiang, J.; Feng, Y.; Wei, Z.; Dai, J. Fabrication of 0-3 Type Manganite/Insulator Composites and Manipulation of Their Magnetotransport Properties. J. Appl. Phys. 2009, 106, 104317. (43) Dix, N.; Muralidharan, R.; Guyonnet, J.; Warot-Fonrose, B.; Varela, M.; Paruch, P.; Sánchez, F.; Fontcuberta, J., On the Strain Coupling across Vertical Interfaces of Switchable BiFeO3–CoFe2O4 Multiferroic Nanostructures. Appl. Phys. Lett. 2009, 95 (6), 062907. (44) MacManus-Driscoll, J. L.; Zerrer, P.; Wang, H.; Yang, H.; Yoon, J.; Fouchet, A.; Yu, R.; Blamire, M. G.; Jia, Q., Strain Control and Spontaneous Phase Ordering in Vertical Nanocomposite Heteroepitaxial Thin Films. Nat. Mater. 2008, 7 (4), 314-320. (45) Bozorth, R.; Tilden, E. F.; Williams, A. J. Anisotropy and Magnetostriction of Some Ferrites. Phys. Rev. 1955, 99, 1788-1798. (46) Hsieh, Y.-H.; Kuo, H.-H.; Liao, S.-C.; Liu, H.-J.; Chen, Y.-J.; Lin, H.-J.; Chen, C.-T.; Lai, C.-H.; Zhan, Q.; Chueh, Y.-L.; Chu, Y.-H. Tuning the Formation and Functionalities of Ultrafine CoFe2O4 Nanocrystals via Interfacial Coherent Strain. Nanoscale 2013, 5, 6219-6223. (47) George, M.; John, A. M.; Nair, S. S.; Joy, P. A.; Anantharaman, M. R. Finite Size effects on the Structural and Magnetic Properties of Sol–Gel Synthesized NiFe2O4 Powders. J. Magn. Magn. Mater. 2006, 302, 190-195. (48) Mahmoud, M. H.; Elshahawy, A.M.; Makhlouf, S. A.; Hamdeh, H. H. Synthesis of Highly Ordered 30 nm NiFe2O4 Particles by the Microwave-Combustion Method. J. Magn. Magn. Mater. 2014, 369, 55-61. (49) Maaz, K.; Kim, G.-H. Single Domain Limit for NixCo1-xFe2O4 (0 ≤ x ≤ 1) Nanoparticles Synthesized by Coprecipitation Route. Mater. Chem. Phys. 1971, 137, 359-364.

25



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

TABLE OF CONTENTS

26


Page 26 of 26

Enhanced Structural and Magnetic Coupling in a Mesocrystal-Assisted

Recommend Documents