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Heteroepitaxy of Fe3O4/Muscovite: A New Perspective for Flexible Spintronics Ping-Chun Wu, Pingfan Chen, Thi Hien Do, Ying-Hui Hsieh, Chun-Hao Ma, Ha Thai Duy, Kun-Hong Wu, Yu-Jia Wang, Hao-Bo Li, Yi-Chun Chen, Jenh-Yih Juang, Pu Yu, Lukas M. Eng, Chun-Fu Chang, Po-Wen Chiu, Liu-Hao Tjeng, and Ying-Hao Chu ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.6b11610 • Publication Date (Web): 21 Nov 2016 Downloaded from http://pubs.acs.org on November 22, 2016

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ACS Applied Materials & Interfaces

Heteroepitaxy of Fe3O4/Muscovite: A New Perspective for Flexible Spintronics Ping-Chun Wu1,2, Ping-Fan Chen3, Thi Hien Do3, Ying-Hui Hsieh2,4, Chun-Hao Ma5, Thai Duy Ha6, Kun-Hong Wu7, Yu-Jia Wang8, Hao-Bo Li8, Yi-Chun Chen7, Jenh-Yih Juang6, Pu Yu8, Lukas M. Eng4, Chun-Fu Chang1, Po-Wen Chiu5, Liu Hao Tjeng1, and Ying-Hao Chu2,3,6*

1

Max Planck Institute for Chemical Physics of Solids, Noethnitzerstr. 40, 01187

Dresden, Germany 2

Department of Materials Science and Engineering, National Chiao Tung University,

Hsinchu 30010, Taiwan 3

Institute of Physics, Academia Sinica, Taipei 11529, Taiwan

4

Institut fur Angewandte Photophysik, Technische Universitat Dresden,

George-Bahr-Str. 1, 01069 Dresden, Germany 5

Department of Electrical Engineering, National Tsing Hua University, Hsinchu

30013, Taiwan 6

Department of Electrophysics, National Chiao Tung University, Hsinchu 30010,

Taiwan 7

Department of Physics, National Cheng Kung University, Tainan City 701, Taiwan

8

Department of Physics, Tsinghua University, Beijing 100084, China

*

[email protected]

Abstract Spintronics has captured a lot of attention since it was proposed. It has been triggering numerous research groups to make their efforts on pursuing spin-related electronic devices. Recently, flexible and wearable devices are in a high demand due to their outstanding potential in practical applications. In

ACS Paragon Plus Environment


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order to introduce spintronics into the realm of flexible devices, we demonstrate that it is feasible to grow epitaxial Fe3O4 film, a promising candidate for realizing spintronic devices based on the tunneling magnetoresistance, on flexible muscovite. In this study, the heteroepitaxy of Fe3O4/muscovite is characterized by x-ray diffraction, high-resolution transmission electron microscopy, and Raman spectroscopy. The chemical composition and magnetic feature are investigated by a combination of x-ray photoelectron spectroscopy and x-ray magnetic circular dichroism. The electrical and magnetic properties are examined to show the preservation of the primitive properties of Fe3O4. Furthermore, various bending tests are performed to show the tunability of functionalities and to confirm that the heterostructures retain the physical properties

under

repeated

cycles.

These

results

illustrate

that

the

Fe3O4/muscovite heterostructure can be a potential candidate for the applications in flexible spintronics. Keywords:

Heteroepitaxy,

Spintronics,

Magnetite,

Muscovite,

Flexible

electronics Introduction Spintronics represents an important research area of solid state devices due to its nature of spin-dependent carrier transport behavior1,2. It adds the spin degree of freedom to modern design of electronic circuits and suggests a new pathway to enhance functionalities of current electronic devices. The discovery of giant magnetoresistance (GMR)3 has boosted the use of spintronics in practical applications, such as hard disk drive, in our daily life. Later, an introduction of the tunneling magnetoresistance (TMR)4 into practical applications has further set up a dominant device architecture in current spintronic devices. In the push of spintronics to next generation, many functional magnetic materials are in a high demand. Half metals stand for an important research direction along this field due to the feature of nearly


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fully spin-polarized electrons at the Fermi level, which is advantageous to further enhance the performance of spintronic devices. Due to the versatility, stability, and ease of fabrication, intense explorations have been made on oxide-based half-metals, such as CrO25, La0.7Sr0.3MnO36, Fe3O47, NiFe2O48 etc. Among them, Fe3O4 is the most attractive material due to its high Curie temperature (Tc) of 858K9 compared to that of La0.7Sr0.3MnO3 (369K)10 and CrO2 (390K)11, which is a dominant factor governing of the thermal stability in device applications. Besides, Fe3O4 possesses different valence states of Fe (Fe2+:d6 and Fe3+:d5) on the octahedral sites. Thus, it was proposed that the electrons can hop rapidly between Fe2+ and Fe3+ ions12, resulting in a much higher conductivity than other ferromagnetic oxides at room temperature. Most importantly, Fe3O4 was predicted to have nearly 100% spin polarization at the Fermi level13. These features make Fe3O4 a powerful candidate for the application in the field of magnetic random access memory and magnetic read heads. However, it is difficult to integrate the magnetite-based devices compatibly with the relevant substrates, such as silicon (Si) or flexible polymers. Up to now, Fe3O4 films can be epitaxially grown on Si (001) substrates only when a double-buffer-layer heterostructure composed of TiN and MgO was used14. When grown on the polymer substrates, it cannot even form single-crystalline structure. In fact, the electronic devices fabricated on flexible substrates have been eagerly expected to meet emerging technological demands that Si-based electronics cannot achieve, such as paper displays or wearable devices. Consequently, it has attracted considerable attention to pursuing flexible spintronics to expand the domain of flexible electronics. For example, there are numerous works demonstrating GMR15,16 and TMR17,18 devices on flexible substrates. However, all these reports are based on polymers substrates, which means that the samples are either poly-crystalline with poor crystallinity or even amorphous. So far, it still remains a major challenge to fabricate oxide-based devices epitaxially on flexible substrates. To our knowledge, no oxide-based half-metals such as Fe3O4 have been directly fabricated on flexible substrates yet. As a result, to advance the field of



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flexible spintronics, it is crucial to build up spintronic devices with high-quality single crystalline Fe3O4 films. To achieve this objective, we noticed that there are reports on the establishment of functional oxide on 2D layered muscovite (Mica)19. A unique feature demonstrated in the study by Ma et. al19 is the heteroepitaxy of functional oxide film on muscovite substrate. Thus, in this study, we choose muscovite as the substrate to pave a pathway to integrate epitaxial Fe3O4 film directly on flexible muscovite. The heteroepitaxy is examined by a combination of various diffraction techniques. The Fe3O4/muscovite heterostructure possesses the intrinsic properties of Fe3O4 based on the electrical and magnetic performance. In order to deliver a new solution for flexible spintronics, the functionalities of the Fe3O4/muscovite heterostructure are tested under various bending conditions. The physical properties of the flexible Fe3O4/muscovite heterostructure against mechanical deformation open a new avenue toward flexible spintronics. Results & Discussion Structural properties In order to characterize the surface condition of substrates and monitor the growth mode of Fe3O4 thin film, in-situ reflection high energy electron diffraction (RHEED) has been employed during the deposition. Fig. 1a shows a typical set of the RHEED patterns taken with the electron beam parallel to [100] and [010] of the muscovite substrate (upper sets in Fig. 1a). The sharp RHEED streaks with the presence of the Kikuchi lines indicate a flat surface of the muscovite substrate. When the deposition started, a few layers of film were deposited on the substrate. These layers were too thin to yield a clear RHEED pattern but blurring the pattern which was contributed from the muscovite substrate. A clear image of RHEED pattern could be observed until the thickness of the film reached ~2-3 nm. These new patterns, lower panel in Fig. 1a, suggest a flat and well-ordered crystalline surface of Fe3O4 film. The simulation of the RHEED patterns was carried out to obtain the in-plane ത ]||Mica[100] and Fe3O4[11ത0]||Mica[010]. As a epitaxial relationship of Fe3O4[112 result, the out-of-plane relation between Fe3O4 and muscovite can also be determined as Fe3O4(111)||Mica(001). To understand the detailed structural information of Fe3O4/muscovite heterostructure, x-ray diffraction (XRD) was employed. The XRD


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2θ-θ scan shown in Fig. 1b exhibits a (111)-oriented Fe3O4 film on (001) muscovite without any secondary crystalline phase. The lattice spacing of Fe3O4 (111) calculated from the XRD result is 4.85Å, which is very close to the bulk value (4.84Å), suggesting that the film is fully strain relaxed. An exhibition of superior crystallinity is revealed based on the full width at half maximum (FWHM) of the rocking curve around Fe3O4 (333) (~1.2°) shown in Fig. 1c. Furthermore, the phi-scan was employed to confirm the epitaxial relationship between Fe3O4 and muscovite, as shown in Fig. 1d. The reflection of Fe3O4 {220} can be detected every 60°, indicating the multi-domain structure since (111)-oriented Fe3O4 film shows three-fold symmetry. The good alignment between muscovite {202} and Fe3O4 {220} peaks at every 120° interval confirms the in-plane epitaxial relationship as Fe3O4[11ത0]||Mica[010], which is consistent with the RHEED patterns. To characterize the crystal symmetry of Fe3O4/muscovite, Raman spectroscopy was performed. For magnetite with cubic inverse spinel structure, there should be five predicted active Raman modes (A1g, Eg and three T2g)20. Typically, only four Raman peaks rather than five can be observed (A1g, Eg and two T2g) in Fe3O421. In Fig. 1e, the Fe3O4/muscovite heterostructure also displays four peaks in the Raman spectrum at 665 cm-1 (A1g), 536 cm-1 (T2g[2]), 303 cm-1 (Eg), 190 cm-1 (T2g[1]). In order to investigate more details of structural relation between Fe3O4 and muscovite, high-resolution transmission electron microscopy (HR-TEM) was adopted. The cross-sectional TEM image represented in Fig. 1f shows a defect-free and coherent interface of the Fe3O4/muscovite heterostructure. The corresponding fast Fourier transform (FFT) patterns of Fe3O4 and muscovite shown in the

inset reveal the epitaxial relationship as Fe3O4(111)||Mica(001) and Fe3O4[11ത0]||Mica[010], consistent with XRD and RHEED results. Based on the above results, we can confirm that high quality (111)-oriented Fe3O4 films with the correct symmetry have been epitaxially grown on muscovite. Chemical Stoichiometry Since Fe ions can have different valence states (Fe2+ and Fe3+) in Fe3O4, it is very important to investigate the valence state of Fe ions in Fe3O4 films to confirm the chemical composition. Thus, x-ray photoelectron spectroscopy (XPS), x-ray absorption spectroscopy, and x-ray magnetic circular dichroism (XAS-XMCD) techniques were employed to characterize the chemical composition. Right after the



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deposition, the sample was transferred in vacuum to a separated chamber for the XPS experiments. In Fig. 2a, we present a wide scan XPS spectrum of the Fe3O4/muscovite thin film, which indicates the purity of the film without elements other than iron and oxygen. Fig. 2b shows the Fe 2p core level spectrum of the film. The chemical composition can be confirmed due to the identical spectral features as a stoichiometric Fe3O4/MgO thin film22. The energy positions of Fe3+ 2p1/2 at 728 eV and Fe3+ 2p3/2 at 710 eV are marked. The peak featured at 708.2 eV, which can be seen clearly in the inset of Fig. 2b, represents the existence of Fe2+. Except for these peaks, no other distinct signals were detected, confirming the valence states of Fe ions in the films are purely composed of a mixture of Fe3+ and Fe2+. Most importantly, the absence of any satellite peaks between Fe3+ 2p1/2 and Fe3+ 2p3/2 indicates the non-existence of Fe2O3 phase, since Fe2O3 generates a satellite peak at 719 eV in XPS measurement. Moreover, the results obtained by the XAS and XMCD are shown in Fig. 2c. The upper panel in Fig. 2c shows the absorption spectra under different directions of magnetic field. A distinct signal of the Fe L-edge can be observed. The difference of spectra under the applied magnetic field of 1 T along opposite directions gives rise to the XMCD spectra shown in the lower panel of Fig. 2c. Three clear peaks at 707.6 eV, 708.6 eV and 709.4 eV can be identified in the spectra across the Fe L2,3 absorption edge. These characteristic peaks represent the different valence states of Fe ions occupied at various sites. The peak at 707.6 eV results from the contribution of Fe2+ ions at the octahedral (Oh) sites. The peaks at 708.6 eV and 709.4 eV are accounted for the contributions of Fe3+ ions situated at the tetrahedral (Td) and Oh sites respectively. Based on the XAS-XMCD results, the antiparallel spins of Fe3+ ions at the Oh and Td sites cancel out to each other, and Fe2+ ions at the Oh sites play the main role in ferrimagnetism, reflecting the magnetic nature and the stoichiometry of the inverse spinel magnetite. Magnetic and Electrical Properties Having established the crystal structure, chemical information, and magnetic nature of magnetite film on muscovite, we now turn our focus on the functionalities of


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the Fe3O4/muscovite heterostructure. Superconducting quantum interference device (SQUID) was used to characterize the macroscopic magnetic properties. Fig. 3a shows the magnetic hysteresis loops of Fe3O4/muscovite at room temperature. The applied magnetic field (H) was set along both in-plane and out-of-plane directions of the heterostructure. The saturated magnetization (Ms) is ~410 emu/cm3 and the coercive field (Hc) is ~400 Oe for both directions, which can be seen more clearly in the Fig. 3b. Based on the magnetic hysteresis loops, the magnetic easy axis is aligned along the in-plane direction of the heterostructure. Moreover, the Verwey transition of Fe3O4, a unique feature of magnetite, was characterized by a combination of the magnetic

characterization

and

electrical

transport

measurement.

In

these

measurements, SQUID was employed to measure the temperature dependence of magnetization (M-T). The sample was cooled under a zero-field condition to 10 K. Then a magnetic field of 100 Oe was applied along the in-plane direction while the temperature was increased from 10 K to room temperature. As shown in Fig. 3c, the value of magnetization is doubled from 90 emu/cm3 to 186 emu/cm3 when the temperature is increased from 104 K to 132 K, suggesting the transition temperature is ~120 K.

In addition, the temperature dependence of resistance (R-T) was

performed in physical property measurement system (PPMS). In the measurement, the temperature was decreased from room temperature to 10 K and the Verwey transition at T~120 K could also be detected. Furthermore, since

the

magnetoresistance (MR) plays a crucial role in the magnetite-based spintronics, we further investigated the MR behaviors of the Fe3O4/muscovite heterostructure. The MR value is defined as [R(H)-R(0)]/R(0), where R(H) and R(0) are the value of resistances with and without magnetic fields, respectively. The resistance of thin film was recorded at three different temperatures (room temperature, above and below Tv) with an applied magnetic field perpendicular to the film. Under the magnetic field of 1 Tesla, the MR values are -0.8%, -1.9% and -2.1% at 300K, 150K and 100K respectively (as shown in Fig. 3d). The MR values are comparable with those measured in the Fe3O4 films on rigid substrates23-25, suggesting the Fe3O4/muscovite heterostructure exhibits superior MR performance, which is a key feature in



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spintronics. Furthermore, no clear MR hysteresis can be observed due to the small coercivity. These evidences strongly suggest that the unique properties of magnetite in the heterostructure have been successfully delivered. Bending Tests In order to demonstrate the applicability of the current design of the heterostructure as a potential candidate for flexible electronics, we carried out the characterization of the functionalities under various bending tests. Firstly, the hysteresis loops were measured to illustrate the variation of the magnetic properties under bending. While measuring, the sample was bent to various radii with the magnetic field applied along three different directions (inset of Fig. 4a). We found that the magnetic properties such as the saturation, remanence and coercivity are retaining their pristine states (Fig. 4a), while the magnetic anisotropy varies with curvatures, as shown in Fig. 4b. The original easy axis was set along the in-plane direction. While bending, the easy axis rotated gradually to the out-of-plane direction with a decrease in the magnetic anisotropy from the bending radius of 10 mm to 2.5 mm. When the bending radius reached the value of 2.5 mm, no clear anisotropy was observed. After the sample was released, the anisotropy would restore to the initial state (Fig. 4c), suggesting a tunable feature of magnetic anisotropy in the heterostructure. Such a phenomenon can be attributed to the modification of magnetostriction since the shape anisotropy prefers an easy axis along the in-plane direction. Furthermore, in order to understand the magnetic properties from the view of microscopic scale, the magnetic domain structure under bending condition was probed by magnetic force microscopy (MFM). Before the measurement, a magnetic field up to 5 T was applied along the in-plane direction to align the magnetic domains. After that, the sample was placed on a customized bending stage with one side being fixed while the other side is movable. Before the experiment, the two sides were adjusted into the same height. The scanned area was located in the center due to the limit of space. By varying the movable side, we could bend the sample with different bending radius. Interestingly, with the bending radius of 90 mm, the magnetic domain size increased clearly, as shown in Fig.


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4d and Fig. 4e. Most importantly, the magnetic domain size could recover to the state of small size, as depicted in Fig 4f, when the sample was released. In a magnetic system, typically the domain size is determined by several energy terms, including the magnetostatic, magnetocrystallline, magnetostriction, and domain wall energies. In these terms, the one coupled with strain strongly is the magnetostriction. Our case can be regarded as the inverse effect of magnetostriction. The strain can produce a change in its preferred magnetization direction. The way we bent the sample can impose a compressive strain along the in-plane direction and Fe3O4 is known to have a positive magnetostriction constant[26]. Under a compressive strain along the in-plane direction, the easy-axis of Fe3O4 can be gradually rotated to the out-of-plane direction, which is evidenced by the M-H loops under bending in Fig. 4b. This suggests that the imposed strain can cause a rotation of the magnetic moment to the out-of-plane direction, resulting in the enlargement of magnetic domain. After identifying the change in microscopic scale, we examined the macroscopic properties of the heterostructure such as transport properties and magnetoresistance under various bending radii. Inset of Fig. 5a presents a schematic diagram of the setup. In Fig. 5a we show the temperature dependent resistance behavior of Fe3O4/muscovite. It is obvious that the Verwey transition did not vary while bending. The only change is that the resistance was slightly increased but could revert after the sample was released. Additionally, to make Fe3O4/muscovite fit into flexible spintronics, it is important to explore the MR under bending. We measured the MR in various bending radii. The behavior and values of MR under bending conditions, as shown in Fig. 5b, remain basically the same (around -0.8% under 1 T at room temperature). That indicates that the Fe3O4/muscovite heterostructure retains its original MR property under bending and is recoverable. In addition, more bending tests were adopted to build up the mechanical stability and cyclability. In Fig. 5c and 5d, we display the conduction behaviors as a function of bending radius. The change of resistance as a function of bending cycles is shown in Fig. 5e and 5f. The changes in resistance with a bending radius of 5 mm and after a thousand of bending cycles only show a variation less than 10%, suggesting the stability of the heterostructure under bending. The verification of the cyclability



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and endurability of Fe3O4/muscovite heterostructure thus has suggested a new pathway toward flexible spintronics applications. Conclusion In summary, we have fabricated Fe3O4 film on 2D layered muscovite. The epitaxial relation between Fe3O4 and muscovite has been established by RHEED, HR-XRD and HR-TEM. The chemical compositions were examined by XAS-XMCD and XPS. By investigating the magnetic and electrical properties, we have confirmed that the Fe3O4/muscovite heterostructure retains the inherent properties of Fe3O4 for spintronics. In addition, the results of bending tests demonstrate the flexibility and cyclability of this heterostructure, that make it a promising solution for flexible spintronics. Our work advances a critical step to Fe3O4-based flexible spintronics and provides a new playground for practical applications as well as oxide heteroepitaxy for fundamental researches. Besides, as mentioned before, those magnetite-based magnetic tunneling junctions can also be potentially transferred on these flexible 2D materials, which could greatly broaden the applied field of spintronic devices. In the future, more sophisticated Fe3O4-based flexible devices such as trilayer structure TMR devices can be fabricated based on this report.

Experimental Section Sample preparation. The chemical formula of muscovite is KAl2AlSi3O10(OH)2. The muscovite we used in this study is the natural one purchased from The Nilaco Corporation. The dimension of the substrates is 1cm*1cm and, to become flexible, the thickness of muscovite should be thinner than 50 μm. Fe3O4 films were grown on muscovite using an ultra-high vaccum molecular beam epitaxy (MBE) facility equipped with an in-situ RHEED for real-time monitoring. Before the deposition, the substrate was annealed for 2 hours at 400℃ in an oxygen pressure of 3 × 10ି଻ mbar in order to obtain a clear and well-ordered surface. The Fe source was evaporated from a LUXEL Radak effusion cell and the Fe rate of 1 Å/min was calibrated by a


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quartz crystal monitor. During the growth, the substrate temperature was kept at 250℃ in an oxygen pressure of 1 × 10ି଺ mbar. For detailed growth conditions, please refer to ref. (22). The thickness of Fe3O4 is ~200 nm in this study.

Structural analysis. High resolution X-ray diffraction measurements were performed with a high resolution Philips XPert MRD diffractometer using monochromatic Cu Kα1 radiation (λ =1.54056Å). Raman spectroscopy was measured by a backscattering confocal microscope (MFO, Horiba Jobin Yvon) equipped with an excited 532 nm solid state laser and a spectrometer (iHR550, Horiba Jobin Yvon). Cross-sectional TEM specimen was prepared by focused ion beam technique (FEI Nova 200). TEM specimen was then examined in a JEOL JEM ARM 200F microscope.

Chemical stoichiometry. The XPS data were collected in situ using 1486.6 eV photons (monochromatized Al Kα light) with a Scienta R3000 electron energy analyzer in normal emission geometry at room temperature. The XAS and XMCD techniques spectroscopies were performed at the Dragon beamline BL11A in the National Synchrotron Radiation Research Center (NSRRC), Taiwan.

Magnetic measurements. The magnetic hysteresis loops and temperature dependent magnetizations were characterized by Quantum Design MPMs magnetometer. Bending magnetic force microscopy was probed by an Asylum Research Cypher in ambient conditions. The type of tip is the Nanosensors PPP-MFMR-10.

Transportation measurements. Magnetoresistance and temperature dependent resistivity measurements were performed by standard four probe technique using a PPMS by Quantum Design.

Bending tests. Magnetic hysteresis, magnetoresistance, and temperature dependent resistance were measured by taping the sample on the homemade molds with various bending radii. In order to fit the setup of MFM measurement, we also customized a



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homemade bending stage. When the sample was put on the stage, one side of the sample was fixed, the other side was movable to create the bending on the sample. Supporting Information Corresponding

topographic

image

of

Fe3O4/muscovite

during

MFM

measurement.

Acknowledgements This work is supported by the Ministry of Science and Technology under Grant Nos. MOST 103-2119-M-009-003-MY3 and MOST 104-2628-E-009-005-MY2. We would like to thank Dr. X. H. Liu for his skillful assistance in operating UHV facilities. References [1] Wolf, S. A.; Awschalom, D. D.; Buhrman, R. A.; Daughton, J. M.; von Molnár, S.; Roukes, M. L.; Chtchelkanova, A. Y.; Treger, D. M., Spintronics: A Spin-Based Electronics Vision for the Future. Science 2001, 294, 1488-1495. [2] Žutić, I.; Fabian, J.; Das Sarma, S., Spintronics: Fundamentals and Applications. Rev. Mod. Phys. 2004, 76, 323-410. [3] Baibich, M. N.; Broto, J. M.; Fert, A.; Van Dau, F. N.; Petroff, F.; Etienne, P.; Creuzet, G.; Friederich, A.; Chazelas, J., Giant Magnetoresistance of (001)Fe/(001)Cr Magnetic Superlattices. Phys. Rev. Lett. 1988, 61, 2472-2475. [4] Miyazaki, T.; Tezuka, N., Giant Magnetic Tunneling Effect in Fe/Al2O3/Fe Junction. J. Magn. Magn. Mater. 1995, 139, L231-L234. [5] Schwarz, K., CrO2 Predicted as a Half-Metallic Ferromagnet. J. Phys. F. Met. Phys. 1986, 16, L211. [6] Park, J. H.; Vescovo, E.; Kim, H. J.; Kwon, C.; Ramesh, R.; Venkatesan, T., Direct Evidence for a Half-Metallic Ferromagnet. Nature 1998, 392, 794-796.

[7] Zhang, Z.; Satpathy, S., Electron States, Magnetism, and the Verwey Transition in Magnetite. Phys. Rev. B 1991, 44, 13319-13331. [8] Lüders, U.; Barthélémy, A.; Bibes, M.; Bouzehouane, K.; Fusil, S.; Jacquet, E.; Contour, J.; Bobo, J.; Fontcuberta, J.; Fert, A.; NiFe2O4: A Versatile Spinel Material Brings New Opportunities for Spintronics. Adv. Mater. 2006, 18, 1733-1736


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Fig. 1 | Structural properties (a) RHEED patterns of muscovite (upper sets) and Fe3O4 (lower sets) (b) Out-of-plane X-ray 2θ-θ diffraction of Fe3O4/muscovite. (c) Rocking curve of Fe3O4(333). (d) Phi scan of muscovite{202} and Fe3O4{220} (e) Raman spectroscopy of Fe3O4/muscovite. (f) HR-TEM cross-sectional image at the interface and corresponding FFT patterns in the insets.



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Fig. 2 | X-Ray Photoelectron Spectroscopy and X-Ray Magnetic Circular Dichroism (a) A wide XPS scan of Fe3O4. (b) High-resolution XPS of Fe 2p core level. Inset shows the fitting peaks of Fe 2p3/2. (c) (Top) XAS spectrum of Fe3O4. (Bottom) Fe L2,3 edge XMCD spectrum of Fe3O4


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Fig. 3 | Magnetic, transport and magneto-transport properties. (a) Hysteresis loops with magnetic field along in-plane direction (red) and out-of-plane direction (blue). (b) An enlarged diagram of hysteresis loops. (c) Temperature dependent resistance (blue) and temperature dependent magnetization (red). (d) Magnetic field dependent resistivity at different temperature.



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Fig. 4 | Magnetic response under bending. (a) Hysteresis loops under various bending radius with in-plane magnetization. (b) Hysteresis loops under various bending radius with out-of-plane magnetization. (c) Hysteresis loops after the sample was released with the magnetization from three different directions. Lower panels are MFM images for (d) as grown, (e) bending down to 50 µm and (f) released.


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Fig. 5 | Transport and magneto-transport properties under bending. (a) Temperature dependent resistance under various bending radius. The inset shows the setting of the measurement for R-T and MR. (b) Magnetoresistance under various bending radius. (c)(d) Resistance of Fe3O4/muscovite heterostructure under various bending radius. (e)(f) The cyclability of Fe3O4/muscovite heterostructure.



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ToC graphic


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Muscovite: A New ... - ACS Publications

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