Magnetoelectric Coupling, Ferroelectricity, and Magnetic Memory

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Magnetoelectric coupling, ferroelectricity, and magnetic memory effect in double perovskite LaNiNbO 3

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Koushik Dey, Ankita Indra, Debajyoti De, Subham Majumdar, and Saurav Giri ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.6b02990 • Publication Date (Web): 02 May 2016 Downloaded from http://pubs.acs.org on May 9, 2016

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ACS Applied Materials & Interfaces

Magnetoelectric coupling, ferroelectricity, and magnetic memory effect in double perovskite La3Ni2NbO9 K. Dey,† A. Indra,† D. De,†,‡ S. Majumdar,† and S. Giri∗,† Department of Solid State Physics, Indian Association for the Cultivation of Science, Jadavpur, Kolkata 700032, India, and Dept. of Physics, The Neotia University, D. H. Road, 24 PGS(S), W. B. 743 363, India E-mail: [email protected]

Abstract We observe ferroelectricity in an almost unexplored double perovskite La3 Ni2NbO9. Ferroelectricity appears below ∼ 60 K, which is found to be correlated with the significant magnetostriction. A reasonably large value of spontaneous electric polarization is recorded to be ∼ 260 µC/m2 at 10 K for E = 5 kV/cm, which decreases significantly upon application of magnetic field (H), suggesting considerable magnetoelectric coupling. The dielectric permittivity is also influenced by H below the ferroelectric transition. The magnetodielectric response scales linearly to the squared magnetization, as described by the Ginzburg-Landau theory. Meticulous studies of static and dynamic features of dc magnetization and frequency dependent ac susceptibility results suggest spin-glass state below 29 K. Intrinsic magnetic memory effect is observed ∗ To

whom correspondence should be addressed of Solid State Physics, Indian Association for the Cultivation of Science, Jadavpur, Kolkata 700032, India ‡ Dept. of Physics, The Neotia University, D. H. Road, 24 PGS (S), W. B. 743 363, India † Department

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from zero-field cooled magnetization and isothermal remanent magnetization studies, also pointing spin-glass state below 29 K. Appearance of ferroelectricity together with a significant magnetoelectric coupling in absence of conventional long range magnetic order is promising for searching new magnetoelectric materials. Keywords: Magnetoelectric coupling, ferroelectricity, spin-glass, memory effect, double perovskite

Introduction Concomitant occurrence of spontaneous magnetic and polar order in a chemically single phase compound attracts the community for the fundamental interests as well as technological applications.1–4 In case of multiferroic order the cross coupling between magnetic and polar order is termed as magnetoelectric (ME) coupling. This provides additional degrees of freedom where magnetic or electric polarization is sensitive to both the electric and magnetic fields. The ME coupling is not only confined to the multiferroics 5 this was first discovered in Cr2O3 , which is not a typical mutiferroic material.11–13 Recently, the ME coupling has been explored in few multi-glass materials.6–10,14–21 In fact, spin-glass (SG) transition was recently verified in a classical multiferroic compound BiFeO3 .22 The SG transition has also been observed in very few well characterized multiferroic materials such as LuFe2 O4−δ 23 and PbFe0.5Nb0.5O3 .24,25 This attracts considerable attention and opens up an issue on possible coexistence of ferroelectricity and SG state with a significant ME coupling. The compound of our interest, La3Ni2NbO9 , belongs to the double perovskite of A3 B2 B'O9 − type having 2:1 ratio between B and B' . This compound is almost unexplored, except for a single report on x-ray diffraction studies and thermal variation of conductivity.26 Chemically single phase could be obtained when synthesis was performed using solid state reaction. The x-ray diffraction pattern could be fitted in the monoclinic P21/n space group satisfactorily. The low electrical conductivity (∼ 1 S/cm) has been reported from the thermal variation of dc conductivity, which decreased considerably with decreasing temperature for La3Ni2NbO9 . Few reports are available on the isomorphous series of compounds with A = La in A3B2B'O9 , displaying dissimilar magnetic properties depending on different B and B' 2 ACS Paragon Plus Environment

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.27–30 The B and B' in La3B2B'O9 exist in trivalent and pentavalent states, respectively. The influence of pentavalent B' on the magnetic properties was reported in La3Co2B'O9 (B' = Nb5+ and Ta5+ ) .27 The interplay between antiferromagnetic (AFM) Co2+−O−Co2+ and Co2+−O−M5+−O−Co2+ ferromagnetic (FM) super exchange interactions were proposed for significant changes in the ordering temperature. Low temperature neutron diffraction study of La3Co2SbO9 confirmed that FM ordering temperature at 55 K was strongly dominated by the Co2+−O−Sb5+ −O−Co2+ super exchange interaction.28 It was further suggested that nature of FM order did not resemble typical long range magnetic order, proposing a significant magnetic frustration. A relaxor FM bahavior has been proposed for La3Ni2SbO9 below 105 K.30 At 5 K any magnetic diffraction peak could not be detected from the neutron diffraction studies, further suggesting the relaxor behavior. In this article we report hitherto unexplored magnetic and ferroelectric properties of La3Ni2NbO9 . The compound exhibits a spontaneous electric polarization (P) below ∼ 60 K (Tc) which is correlated to the observed magnetostriction, revealing a maximum close to Tc. A significant ME coupling is evident below ferroelectric Tc, which becomes significant below spin-glass transition. Field cooled effect of dc magnetization, zero-field cooled memory effect, memory effect in relaxation dynamics, isothermal remanent magnetization, and frequency dependence of ac susceptibility results reveal typical SG behavior, suggesting an insulating SG transition at ∼ 29 K (Tg). Intriguingly, the results are very similar to those observed in corresponding studies of the archetypal RKKY spin glasses such as Ag(Mn), Cu(Mn), etc.31–34 Emergence of ferroelectricity accompanied by the significant ME coupling in absence of conventional long range magnetic order in La 3Ni2NbO9 attracts the community for searching new ME materials.



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Figure 1: (a) X-ray powder diffraction patterns (symbols) with Rietveld refinement (solid curve) of diffraction pattern at 300 K. (b) Arrangements of Ni/NbO6 octahedra and La atoms. (c) XPS focusing on Nb oxidation state. (d) SEM image. Element mapping analysis of (e) a particle for (f ) La, (g) Ni, and (h) Nb of La3 Ni2 NbO9 .

Experimental details Polycrystalline compound with composition La3Ni2NbO9 was prepared using solid-state reaction.26 The crystal structure and chemical composition were confirmed using powder x-ray diffraction studies, as recorded in a SEIFERT x-ray diffractometer (Model: XRAY3000P) using Cu Kα radiation. The data were analyzed using Rietveld refinement with FULLPROF softwares. X-ray photoemission spectroscopy (XPS) was recorded in a spectrometer of Omicron Nanotechnology. The average grain sizes were monitored from a scanning electron microscopy (JSM-6700F, JEOL). The element mapping analysis was done using transmission 4 ACS Paragon Plus Environment

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electron microscopy (TEM) o f the JEOL JEM, 2100F field emission microscope equiped with an energy dispersive x-ray spectrometer. Thermal variation of heat capacity was measured using a home built set up coupled to a cryogen-free cryocooler (JANIS, USA). The magnetostriction was measured by capacitive method using a dilatometer where magnetic field was applied field along the length of the sample. Powder sample pressed into a pellet was used for the dielectric measurements using a E4980A LCR meter (Agilent Technologies, USA) equipped with a cryogen-free cryocooler (JANIS, USA). The pyroelectric current (Ip ) was recorded in an electrometer (Keithley, model 6517B) at a constant temperature sweep rate. In all the measurements electrical contacts were fabricated using an air drying silver paint. For measurement of P in magnetic field (H), the field was applied during cooling cycle using a commercial superconducting magnet system (Cryogenic Ltd., UK). The measurement was done in the warming cycle in zero magnetic field. The dc magnetization and ac susceptibility were measured in a commercial magnetometer of Quantum Design (MPMS, evercool) both in zero-field cooled (ZFC) and field cooled (FC) protocols. For ZFC and FC protocols, sample was cooled in zero-field and static magnetic field (H), respectively.

Results and discussions X-ray diffraction pattern at 300 K is depicted in Figure 1a. The continuous curve shows the Rietveld refinement using monoclinic P21/n space group satisfactory, as also reported for the isomorphous series of compounds.

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The diffraction peaks and the difference plot are

shown below the diffraction pattern, indicating absence of impurity phase. A schematic representation of octahedral arrangements is depicted in Figure 1b. Positional coordinates in the schematic representation are obtained from the Rietveld refinement at 300 K. The XPS spectrograph of Nb(3d) contribution is shown in Figure 1c. In accordance with the previous report35 the deconvoluted components, as shown by the continuous curves, are depicted in the figure with peak positions at 210.5 and 207.1 eV corresponding to Nb 3d3/2 and 3d5/2 components, respectively. The results indicate that Nb in the compound exists in Nb5+



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state. The grain size and morphology as obtained from the scanning electron microscopy are depicted in Figure 1d. Average particle size is found ∼ 0.8 µm. The element mapping of a particle is recorded using TEM. Nearly uniform element mapping of a particle [Figure 1e] are displayed in Figures 1f, 1g, and 1h for La, Ni, and Nb, respectively.

Figure 2: T variations of (a) ZFC and FC magnetization. Inset of (a) depicts difference between FC and ZFC magnetization with T. (b) Inverse of susceptibility (χ−1 ) with T. Straight line shows the Curie-Weiss fit. (c) Magnetic hysteresis loops recorded in selective temperatures. Inset depicts the plot of HC with T. (d) T variation of heat capacity (Cp ). Inset shows the plot of dCp /dT vs T highlighting Tg and Tc . Thermal (T) variations of ZFC (MZFC) and FC (MFC) magnetization recorded at magnetic field, H = 100 Oe, are displayed in Figure 2a. The MZFC depicts quite a sharp peak at 29 K (Tg ). The MFC exhibits a broadened maximum below Tg , as commonly observed for SG systems.36 The MFC deviates from MZFC below ∼ 55 K (≫ Tg ), as evident in the inset of Figure 2a by the difference plot between MFC and MZFC . Inverse of susceptibility (χ−1) as a 6 ACS Paragon Plus Environment

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function of T is plotted in Figure 2b. The χ−1(T) deviates from linear Curie-Weiss (CW) behavior below ∼ 250 K. The linear CW fit provides effective paramagnetic moment (µeff ) ∼ 2.82 µB with a CW temperature ∼ 136 K. The value of µeff almost matches with the theoretical spin-only value (2.83 µB), pointing that Ni in La3Ni2NbO9 exists in high-spin Ni2+ state. Magnetic hysteresis loop is depicted at 5 K in Figure 2c. A reasonable value of coercivity (HC) is observed as ∼ 1.3 kOe at 5 K, which decreases sharply with increasing T and nearly disappears around Tg as evident in the inset of figure. The magnetization curve does not show any saturating trend at 50 kOe. The value of M (50 kOe) decreases slowly with increasing T until Tg and it decreases rapidly above ∼ 60 K. Notably, a nonlinear magnetization curve with a significantly large value of M (50 kOe) is evident at 60 K (≫ Tg ), as depicted in Figure 2c. T variation of heat capacity (Cp ) is depicted in Figure 2d. Weak anomalies are indicated in T variation of Cp close to Tg and ferroelectric Tc (as obtained from Figure 6c). Signatures of Tg and Tc are evident in the dCp /dT vs T plot, as depicted in the inset of figure. The ac susceptibility data at different frequencies (f ) are recorded to probe origin of transition at Tg. The real component of ac susceptibility (χ′ac) with T is depicted in Figure 3a around Tg at different f. The peak position of χ′ac(T) for the lowest-f at 7.0 Hz is observed at ∼ 30.7 K, which is slightly higher than the observation of Tg at ∼ 29 K, as obtained from the dc magnetization. The peak position shifts toward higher T with increasing f . This f dependent shift primarily distinguishes nature of transition. Considering ω = 2πf, the values of ∆Tg /[Tg ∆(log ω)] is found to be ∼ 0.005, which lies in the range 0.005−0.010, as reported for RKKY SGs. 36 To test it further, the f dependent shift is analysed using Vogel-Fulcher law described τ = τ'0exp[Ea/kB(T-T'0)],

(1)

where being the characteristic relaxation time, Ea is the anisotropy energy barrier, T'0 is a phenomenological parameter, and τ is the inverse of measuring frequency (1/2πf). A satisfactory fit using Vogel-Fulcher law is depicted in Figure 3b, which provides T'0 ≈ 28 K



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Figure 3: (a) T variation of χ′ac at different f. Verification of peak-shift with f by (b) Vogel-Fulcher law and (c) dynamical scaling law. and τ'0 ≈ 4.5 ×10−13 s. The f dependent shift is further corroborated with the dynamical scaling law given by τmax = τ0 ζ zν .

(2)

Where ζ = T0 /(T − T0 ) is the correlation length, τ0 is the microscopic flipping time, z is the dynamic exponent, ν is the spin-correlation length exponent, and T0 provides the dc value for f = 0 (Tg ). The satisfactory fit using dynamical scaling law is shown in Figure 3c by the straight line. Here, T0 ≈ 30 K, τ0 ≈ 1.3 × 10−13 s, and zν ≈ 6.5, as obtained from fit. The 8 ACS Paragon Plus Environment

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results clearly indicate that the fitted parameters, as obtained from the Vogel-Fulcher and the dynamical scaling laws, are close to those observed for the SG systems.36 We note that the values of T'0 and T0 are 28 and 30 K, respectively, which are close to Tg = 29 K. The values of τ'0 and τ0 are ~ 4.5 × 10−13 and ~ 1.3 × 10−13 s, respectively, which exist in the range ~ 10−12 − 10−14 s proposed for SGs.37 The value of zν ≈ 6.5 is also within the range 4−12 typically found for SGs.37 The experiment to study the memory effect in ZFC protocol is used for further characterization of the SG state below Tg .38,39 The results are depicted in Figures 4a-c. First, sample is cooled in zero field in a fixed temperature sweep rate of 1 K/min and during this cooling process, the sample temperature (Tw) is halted at 19 K (< Tg) for different waiting time (tw), as depicted in Figure 4a. After completing tw, sample is further cooled to the base temperature at 5 K and MZFC is recorded in 50 Oe with the same temperature sweep rate during warming cycle. Although magnetization measurement is carried out continuously, the MZFC curve for different tw exhibits a ‘dip’ at Tw, as evident in Figure 4a. The MZFC data without any halt during cooling is depicted as the broken curve, which is called as a reference curve. The MZFC curves for different tw, subtracted from the reference curve, defined as ∆M, is shown in Figure 4b. The ∆M − T plots at different tw shows a ‘dip’ at Tw and depth of the ‘dip’ increases with increasing tw . When halt is considered at two different temperatures (Tw1 and Tw2) below Tg, two ‘dip’s are observed as depicted in Figure 4c, which are further highlighted in the inset of Figure 4c. During ageing process with a t w at Tw, the system is left unperturbed and it rearranges the spin configuration toward the equilibrium. This equilibrium state is frozen upon further cooling and can be retrieved on reheating at Tw. This is manifested by the ‘dip’ at Tw and is termed as a memory effect.



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Figure 4: Thermal (T) variation of (a) ZFC magnetization (broken curve) considered as “Reference” curve and other curves for different waiting time (tw ) during cooling, and (b) difference plot (∆M) between “Reference” curve and curves after different tw. (c) T variation of “Reference” curve and curves for same waiting time (tw = 7200 s) at two different temperatures (tw1 and tw2 ) during cooling. The ∆M with T is shown in the inset. (d) The experimental protocol of recording IRM is described. (e) IRM at different th for a fixed t'w. (f) IRM at different t′w for a fixed th.

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Different experiment protocols clearly demonstrate systematic intrinsic memory effect, as typically observed for classical SGs. 36 Recently, the comprehensive experiment protocols have been identified by Mathieu et al. to characterize various canonical SG systems using investigation on various protocols of isothermal remanent magnetization (IRM).31–34 These experimental protocols for recording IRM are used for characterizing SG state below Tg. The experimental protocol used is described in Figure 4d. The sample temperature is initially decreased to 19 K at a rate of 1 K/min and the stabilized sample temperature is kept fixed at Th for a time period (t'w). A small magnetic field is then applied for a time period (th ). After switching off the magnetic field the sample is further cooled down to the base temperature at 5 K in zero field. From 5 K the sample is heated continuously at a rate of 1 K/min. In all the thermal cycling process magnetization measurements are carried out in zero field. The results of which are depicted in Figures 4e and 4f for different t'w and th. As displayed in Figure 4e, t'w is kept fixed at 5 s and values of th are varied in the range 3600−7200 s. With increasing the remanent magnetization increases as evident in the figure. Figure 4f depicts the results for different t'w with a fixed th = 3600 s. With increasing t'w the remanent magnetization decreases significantly. Additionally, Figures 4e and 4f depict that remanent magnetization starts decreasing around Th and vanishes rapidly above Th. The results clearly demonstrate that dynamics of spins durin t'w and th significantly influence the remanent magnetization and thermal history during cooling can be memorized during heating process in remanent magnetization, as meticulously studied for classical SGs.31–34 Mathieu et al. elegantly demonstrated that IRM protocols can identify the spindimensionality (Ising, XY, Heisenberg) of a three-dimensional SG.34 In case of Heisenberg interaction existence of Dzyaloshinsky−Moriya interaction provides an excess moment of the IRM, which is manifested by a small increase in remanent magnetization just above Th. Nonexistence of excess moment in the current investigation may suggest that insulating SG state of three-dimensional La3Ni2NbO9 does not reveal Heisenberg spin interaction.



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Figure 5: (a) Magnetic relaxation at 18 K and 50 Oe for t1 and t3 after cooling in ZFC mode with an intermediate cooling and measurement at 12 K for t2. Inset shows the relaxation in 50 Oe for t1 + t3 following single stretched exponential function. (b) Magnetic relaxation at 18 K in zero-field for for t1 and t3 after FC in 50 Oe with an intermediate cooling at 10 K and measurement for t2. Inset shows the relaxation at 18 K for t1 + t3 following single stretched exponential function.

Studies of memory effects are further extended in the relaxation dynamics, which are summarized in Figure 5. Figure 5a displays isothermal magnetic relaxation at 18 K measured in 50 Oe after zero-field cooling from 75 K, below which ZFC and FC magnetization deviates from each other. Initially, isothermal relaxation is recorded for a time period t1 . At the end of t1 sample temperature is decreased to 12 K. The relaxation is further recorded through t2 at 12 K. Finally, temperature is again returned to 18 K and relaxation is measured for t3. As shown in the inset of Figure 5a the relaxation dynamics of magnetization for t1 and t3 follow a stretched exponential function, M(t) = M0 + Mg exp[−(t/τ )β], where M0 and Mg are the ferromagnetic (FM) and exponential components of magnetization. β is an exponent which lies in the range 0 < β < 1 for SG, indicating the relaxation against multiple relaxation barriers.36 The fit using stretched exponential function provides τ = 957 s and β = 0.47. Similar results are observed at 18 K in the relaxation dynamics measured in zero-field after field-cooling in 50 Oe from 75 K, which is depicted in Figure 5b. The parameters, as obtained from the fit using stretched exponential function for t1 and t3 shown in the inset, are τ = 810 s and β = 0.50. This indicates that intermediate changes in condition by decreasing temperature do not alter the relaxation dynamics for both the measurements in ZFC and 12 ACS Paragon Plus 12 Environment

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FC conditions. Rather, it always repeats the previous history. These are the manifestations of memory effect in the relaxation dynamics.

Figure 6: T variations of (a) real (ε') and (b) imaginary (ε′′ ) components of ε at different f, (c) electric polarization (P) for different poling fields (E), (d) P for + 2 kV/cm poling field in zero-field and 90 kOe. Inset of (a) dε′ /dT with T at different f . Inset of (b) shows T variation of dc conductivity. Inset of (d) Ip with T for + 2 kV/cm poling field in zero-field and 90 kOe. The AFM Co2+−O−Co2+ and FM Co2+−O−M5+−O−Co2+ super exchange interactions have been proposed in isostructural La3Co2SbO9 .27,28 Analogous to this scenario, an interplay between AFM Ni2+−O−Ni2+ and FM Ni2+−O−Nb5+−O−Ni2+ super exchange interactions



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is exceedingly probable in La3Ni2NbO9 , which needs to be confirmed from the neutron diffraction studies. Therefore, coexistence of competing of FM and AFM interactions can be the origin of the magnetic frustration in this system. The disorder and frustration are two primary conditions for occurrence of SG state. Neutron diffraction studies in the isostructural compounds indicated significant distortions in the B 2+/B' 5+O6 octahedra for La3BB'2O9 through the irregular bond lengths at room temperature as well as in the thermal variations.28,40 In fact, random occupancy of Ni and Nb at 2d site of P21 /n space group is proposed from Rietveld refinement of the x-ray diffraction data. This structural disorder may bring in disorder in the spin degrees of freedom and assists for SG state in La3Ni2NbO9 . The response to the thermal variation of electric polarization is monitored by recording dielectric permittivity (ε) with T . The real (ε') and imaginary (ε'') components of ε with T are depicted in Figures 6a and 6b, respectively.

As shown in Figure 6a thermal variation

shows a decreasing trend with decreasing temperature and a change of slope is observed around 60 K, below which it shows weak f dependent behavior. In the inset of the figure dε'/dT is plotted with T at different f and indicates a broadened signature of an anomaly around 75 K. This is also further indicated in ε''(T), as depicted in Figure 6b. Around this weak signature in ε(T) the spontaneous electric polarization appears as evident in Figures 6c and 6d. We have measured dc conductivity as depicted in the inset of Figure 6b. The results demonstrate high resistivity (∼ 0.25 GΩ-cm around 100 K), below which spontaneous polarization appears. The pyroelectric currents are recorded in different conditions of applied poling fields (E). Example of a thermal variation of Ip at E = + 2 kV/cm is depicted in the inset of Figure 6d. Time integration of Ip(T) provides P(T). The P(T) at different E are depicted in Figure 6c. It turns out that P increases with increasing E. The value of P is reasonably large to be ∼ 260 µC/m2 at 10 K for E = 5 kV/cm. The switching of P due to opposite poling field is depicted in Figure 6c, as expected for ferroelectricity. The P is strongly influenced by H below FE Tc as depicted in Figure 6d. In the inset of the figure thermal variations of Ip in zero-field and 90 kOe are displayed for E = + 2 kV/cm. The 14 ACS Paragon Plus 14 Environment

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value of P decreases upon application of magnetic field (H), as also observed in Fe2 TiO5 . 18 The change in P increases with decreasing temperature and becomes significant as ∼ 14 % at 10 K for H = 90 kOe.

Figure 7: (a) Percentage of MD defined as ε′(H)/ε′(0)-1 with H at selective T. (b) Plot of ε′(H)/ε′(0)-1 with square of magnetization (M2) at 15 and 25 K. T variations of (c) ∆L/L in zero-field and 50 kOe and (d) difference plot defined as [∆L(0)-∆L(H )]/L. We define magnetodielectric (MD) response as, ε′(H)/ε′(0)-1. The MD (%) with H at different T is depicted in Figure 7a. The correlation of MD to the square of magnetization (M) is shown in Figure 7b. We note that MD increases significantly with decreasing T and becomes considerable below Tg. Thermal variation of MD is entirely different from the variation of ∆L/L with T, as also evident in Figures 7c and 7d. In Figure 7d the value of ∆L/L is maximum around Tc and it decreases significantly when T deviates from ferroelectric Tc. In addition, the value of ∆L/L(%) is ∼ 10-3, which is nearly two orders of 15 ACS Paragon Plus 15 Environment


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magnitude lower than the value of MD(%). This indicates that magnetostriction does not have significant role in the observed MD response. The MD effect can be phenomenologically described by the Ginzburg-Landau theory for second-order phase transition and is attributed to the ME coupling term γP 2 M 2 in the thermodynamic potential (Φ) given by Φ = Φ0 + αP2 + (β/2)P4 - PE + α'M2 + (β'/2)M4 - MH + γP2M2.

(3)

Where α, β, α', β ' , and γ are the constants and functions of temperature. Here, the plot of [ε′(H )/ε′(0)-1](%) vs M 2 at 15 and 25 K are depicted in Figure 7b. We note that at 25 K the linearity of the curve holds below ∼ 10 kOe, as observed for CoCr2S4 41 as well as CoCr2O4 .42,43 At 15 K the plot is linear up to 90 kOe as reported for BiMnO3 .44 This indicates that the ME coupling term γP2M2 of the Ginzburg-Landau theory [Eq. (3)] is significant for La3Ni2NbO9. In addition to the SG state, emergence of ferroelectricity with a significant ME coupling is interesting, because the ME coupling does not involve any long range magnetic order. Since La3Ni2NbO9 is not aconventional multiferroic material, appearance of ME coupling is intriguing and attracts the community. Here, ferroelectricity appears much above Tg. Although a non-linear magnetization curve with a significant value of magnetization at 50 kOe is observed as evident in Figure 2c, around which ferroelectricty emerges, occurrence of ferroelectricity does not involve any long range magnetic order. We note that an evident signature of maximum is observed in ∆L/L(T) even in absence of magnetic field, around which ferroelectric order occurs. This points to the fact that striction is somewhat correlated to the appearance of ferroelectricity. In order to correlate large ε with the crystal structure in Ba3B2B′O9 , Lufaso proposed that an off-centering of Nb5+ in NbO6 octahedra is probably driven by the asymmetry in the O bonding network and further aided by the second-order Jahn-Teller distortion of d0 in Nb5+ .40 In fact, significant covalency of Nb5+ provides more probability for occupying a distorted coordination environment as revealed


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by the off-centered shift of Nb in NbO6 octahedra.45 This might be manifested by the maximum in thermal variation of ∆L/L in the current investigation. In order to search origin of ferroelectricity, meticulous structural studies are proposed using synchrotron diffraction studies for La3Ni2NbO9 .

Conclusion In conclusion, coexistence of spin-glass state and ferroelectricity is observed in double perovskite La3Ni2NbO9 . The competing ferromagnetic and antiferromagnetic interactions associated with the structurally driven disorder is suggested for the occurrence of spin-glass state. On the other hand, magnetostriction is found to be correlated with the emergence of ferroelectricity. A significant magnetoelectric coupling is observed below Tg. Absence of long range magnetic order indicates that the compound is not a conventional multiferroic material. Significant magnetoelectric coupling in the material is promising for searching new magnetoelectric materials without multiferroic order. Acknowledgment S.G. acknowledges the support from DST, India project (No.:SB/S2/CMP-029/2014). A.I. and K.D. wishes to thank INSPIRE, DST and CSIR, India for the fellowship. The authors would like to thank Professor Prabhat Mandal for providing the facility of magnetostriction measurement. The authors also acknowledge Dr. S. K. De for the Rietveld refinement.

References [1] Fiebig, M. Revival of the Magnetoelectric Effect. J. Phys. D: Appl. Phys. 2005, 38, R123-R125. [2] Cheong, S. W. and Mostovoy, M. Multiferroics: a Magnetic Twist for Ferroelectricity. Nat. Mater. 2007, 6, 13-20. 17 ACS Paragon Plus 17 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 18 of 23

[3] Scott, J. F. Applications of magnetoelectrics. J. Mater. Chem. 2012, 22, 4567-4574. [4] Meher, K. R. S. Preethi; Martin, C.; Caignaert, V.; Damay, F. and Maignan, A. Multiferroics and Magnetoelectrics: A Comparison Between Some Chromites and Cobaltites. Chem. Mater. 2014, 26, 830-836. [5] Su, J.; Yang, Z. Z.; Lu, X. M.; Zhang, J. T.; Gu, L.; Lu, C. J.; Li, Q. C.; Liu, J.-M.; and Zhu, J. S. Magnetism-Driven Ferroelectricity in Double Perovskite Y2NiMnO6 . ACS Appl. Mater. Interfaces 2015, 7, 13260-13265. [6] Shvartsman, V. V.; Bedanta, S.; Borisov, P.; Kleemann, W.; Tkach, A.; and Vilarinho, P. M. (Sr,Mn)TiO3 : A Magnetoelectric Multiglass. Phys. Rev. Lett. 2008, 101, 165704165708. [7] Kleemann, W.; Bedanta, S.; Borisov, P.; Shvartsman, V. V.; Miga, S.; Dec, J.; Tkach, A. and Vilarinho, P. M. Multiglass Order and Magnetoelectricity in Mn2+ Doped Incipient Ferroelectrics. Eur. Phys. J. B 2009, 71, 407-410. [8] Singh, K.; Maignan, A.; Simon, Ch.; Hardy, V.; Pachoud, E. and Martin, C. The Spin Glass Delafossite CuFe0.5V0.5O2 : a Dipolar Glass? J. Phys.: Condens. Matter 2011, 23, 126005-126010. [9] Singh, K.; Maignan, A.; Simon, Ch.; Kumar, S.; Martin, C.; Lebedev, O.; Turner, S. and Tendeloo, G. Van Magnetodielectric CuCr0.5V0.5O2 : an example of a magnetic and dielectric multiglass. J. Phys.: Condens. Matter 2012, 24, 226002-226004. [10] Kumar, S.; Singh, K.; Miclau, M.; Simon, Ch.; Martin, C. and Maignan, A. From Spin Induced Ferroelectricity to Spin and Dipolar Glass in a Triangular Lattice: The CuCr1−x Vx O2 (0≤x≤0.5) Delafossite. J. Solid State Chem. 2013, 203, 37-43. [11] Brockhouse, B. N. Antiferromagnetic Structure in Cr2O3 . J. Chem. Phys. 1953, 21, 961-962. 18 ACS Paragon Plus 18 Environment

Page 19 of 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


[12] Iyama, A. and Kimura, T. Magnetoelectric Hysteresis Loops in Cr2O3 at Room Temperature. Phys. Rev. B 2013, 87, 180408(R)-180412(R). [13] Ghosh, A.; Dey, K.; Sabyasachi, Sk.; Karmakar, A.; Majumdar, S. and Giri, S. Colossal Magnetocapacitance Near Room Temperature in Ferromagnetic Cr2O3 Film. Appl. Phys. Lett. 2013, 103, 052412-052416. [14] Choudhury,D.; Mandal, P.; Mathieu, R.; Hazarika, A.; Rajan, S.; Sundaresan, A.; Waghmare, U. V.; Knut, R.;Karis, O.; Nordblad, P. and Sarma, D. D. Near-RoomTemperature Colossal Magnetodielectricity and Multiglass Properties in Partially Disordered La2NiMnO6 . Phys. Rev. Lett. 2012, 108, 127201-127205. [15] Choudhury, D.; Mukherjee, S.; Mandal, P.; Sundaresan, A.; Waghmare, U. V.; Bhattacharjee, S.; Mathieu, R.; Lazor, P.; Eriksson, O.; Sanyal, B.; Nordblad, P.; Sharma, A.; Bhat, S. V.; Karis, O. and Sarma D. D. Tuning of Dielectric Properties and Magnetism of SrTiO3 by Site-Specific Doping of Mn. Phys. Rev. B 2011, 84, 125124-125130. [16] Yamaguchi, Y.; Nakano, T.; Nozue, Y. and Kimura, T. Magnetoelectric Effect in an XY-like Spin Glass System Nix Mn1−x TiO3 Phys. Rev. Lett. 2012, 108, 057203-057207. [17] Yamaguchi, Y. and Kimura, T. Magnetoelectric Control of Frozen State in a Toroidal Glass. Nat. Commun. 2013, 4, 2063-2067. [18] Sharma, S.; Basu, T.; Shahee, A.; Singh, K.; Lalla, N. P. and Sampathkumaran, E. V. Multiglass Properties and Magnetoelectric Coupling in the Uniaxial Anisotropic SpinCluster-Glass Fe2 TiO5 Phys. Rev. B 2014, 90, 144426-144431. [19] Basu, T.; Paulose, P. L.; Iyer, K. K.; Singh, K.; Mohapatra, N.; Chowki, S.; Gonde, B. and Sampathkumaran, E. V. A Reentrant Phenomenon in Magnetic and Dielectric Properties of Dy2BaNiO5 and an Intriguing Influence of External Magnetic Field. J. Phys.: Condens. Matter 2014, 26, 172202-172207.



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 20 of 23

[20] Basu, T.; Mohapatra, N.; Singh, K. and Sampathkumaran, E. V. Magnetic and Magnetodielectric Coupling Anomalies in the Haldane Spin-Chain System Nd2BaNiO5 . Aip Advances 2015, 5, 037128-037134. [21] Karmakar, A.; Dey, K.; Chatterjee, S.; Majumdar, S. and Giri, S. Spin Correlated Dielectric Memory and Rejuvenation in Multiferroic CuCrS2 . Appl. Phys. Lett. 2014, 104, 052906-052910. [22] Singh, M. K.; Prellier, W.; Singh, M. P.; Katiyar, Ram S. and Scott, J. F. Spin-glass Transition in Single-Crystal BiFeO3 . Phys. Rev. B 2008, 77, 144403-144407. [23] Wang, F.; Kim, J.; Kim, Y.-J. and Gu, G. D. Spin-glass behavior in LuFe2 O4+δ . Phys. Rev. B 2009, 80, 024419-024425. [24] Rotaru, G. M.; Roessli, B.; Amato, A.; Gvasaliya, S. N.; Mudry, C.; Lushnikov, S. G. and Shaplygina, T. A. Spin-Glass State and Long-Range Magnetic Order in Pb(Fe1/2 Nb1/2)O3 Seen via Neutron Scattering and Muon Spin Rotation. Phys. Rev. B 2009, 79, 184430-184434. [25] Kleemann, W.; Shvartsman, V. V.; Borisov, P. and Kania, A. Coexistence of Antiferromagnetic and Spin Cluster Glass Order in the Magnetoelectric Relaxor Multiferroic PbFe0.5 Nb0.5O3 . Phys. Rev. Lett. 2010, 105, 257202-257205. [26] Inprasit, T.; Wongkasemjit, S.; Limthongkul, P. and Skinner, S. Synthesis and Electrical Property Study of La3Ni2MO9 (M=Nb and Ta). J. Materials Lett. 2016, 162, 37-39. [27] Fuertes, V. C.; Blanco, M. C.; Franco, D. G.; Paoli, J. M. De; Sánchez, R. D. and Carbonio, R. E. Influence of the B-Site Ordering on the Magnetic Properties of the New La3Co2MO9 Double Perovskites with M = Nb or Ta. Mat. Res. Bull. 2011, 46, 62-69.


Page 21 of 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


[28] Franco, D. G.; Fuertes, V. C.; Blanco, M. C.; Fernańdez-D´ıaz, M. T.; Sánchez, R. D. and Carbonio, R. E. Synthesis, Structure and Magnetic Properties of La3 Co2 SbO9 : A Double Perovskite with Competing Antiferromagnetic and Ferromagnetic Interactions. J. Solid State Chem. 2012, 194, 385-391. [29] Qi, S.; Wei, D.; Huang, Y.; Kim, S. I.; Yu, Y. M. and Seo, H. J. Microstructure of Eu3+ Doped Perovskites-Type Niobate Ceramic La3Mg2NbO9 . J. Am. Ceram. Soc. 2014, 97, 501-506. [30] Battle, P. D.; Evers, S. I.; Hunter, E. C. and Westwood, M. La3 Ni2 SbO9 : a Relaxor Ferromagnet. Inorg. Chem. 2013, 52, 6648-6653. [31] Mathieu, R.; Jönsson, P. E.; Nordblad, P.; Katori, H. A. and Ito, A. Memory and Chaos in an Ising Spin Glass. Phys. Rev. B 2001, 65, 012411-012414. [32] Mathieu, R.; Jönsson, P. E.; Nam, D. N. H. and Nordblad, P. Memory and Superposition in a Spin Glass. Phys. Rev. B 2001, 63, 092401-092404. [33] Mathieu, R.; Hudl, M. and Nordblad, P. Memory and Rejuvenation in a Spin Glass. Europhys. Lett. 2010, 90, 67003-67008. [34] Mathieu, R.; Hudl, M.; Nordblad, P.; Tokunag, Y.; Kaneko, Y.; Tokura, Y.; Katori, H. A. and Ito, Atsuko Isothermal Remanent Magnetization and the Spin Dimensionality of Spin Glasses Phil. Mag. Lett. 2010, 90, 723-729. [35] Liu, H.; Gao, N.; Liao, M. and Fang, X. Hexagonal-like Nb2O5 Nanoplates-Based Photodetectors and Photocatalyst with High Performances. Sci. Rep. 2015, 5, 7716-7724. [36] Mydosh, J. A. Spin Glasses: An Experimental Introduction; Taylor & Francis: London, 1993. [37] Binder, K. and Young, A. P. Spin glasses: Experimental Facts, Theoretical Concepts, and Open Questions. Rev. Mod. Phys. 1986, 58, 801-976. 21 ACS Paragon Plus 21 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 22 of 23

[38] Sun, Y.; Salamon, M. B.; Garnier, K. and Averback, R. S. Memory Effects in an Interacting Magnetic Nanoparticle System. Phys. Rev. Lett. 2003, 91, 167206-167209. [39] De, D.; Karmakar, A.; Bhunia, M. K.; Bhaumik, A.; Majumdar, S. and Giri, S. Memory Fffects in Superparamagnetic and Nanocrystalline Fe50Ni50 alloy. J. Appl. Phys. 2012, 111, 033919-033925. [40] Lufaso, M. W. Crystal Structures, Modeling, and Dielectric Property Relationships of 2:1 Ordered Ba3MM'2 O9 (M = Mg, Ni, Zn; M′ = Nb, Ta) Perovskites. Chem. Mater. 2004, 16, 2148-2156. [41] Dey, K.; Karmakar, A.; Indra, A.; Majumdar, S.; Ru ¨ tt, U.; Gutowski, O.; Zimmermann, M. v. and Giri, S. Thermally Assisted and Magnetic Field Driven Isostructural Distortion of Spinel Structure and Occurrence of Polar Order in CoCr2S4 . Phys. Rev. B 2015, 92, 024401-024407. [42] Sparks, T. D.; Kemei, M. C.; Barton, P. T.; Seshadri, R.; Mun, E.-D. and Zapf, V. S. Magnetocapacitance as a Sensitive Probe of Magnetostructural Changes in NiCr2O4 . Phys. Rev. B 2014, 89, 024405-024410. [43] Mufti, N.; Nugroho, A. A.; Blake, G. R. and Palstra, T. T. M. Magnetodielectric Coupling in Frustrated Spin Systems: the Spinels MCr2 O4 (M = Mn, Co and Ni). J. Phys. Condens. Matter 2010, 22, 075902-075907. [44] Kimura, T.; Kawamoto, S.; Yamada, I.; Azuma, M.; Takano, M. and Tokura, Y. Magnetocapacitance Effect in Multiferroic BiMnO3 . Phys. Rev. B 2003, 67, 180401(R)180404(R). [45] Li, M.-R.; Stephens, P. W.; Retuerto, M.; Sarkar, T.; Grams, Ch. P.; Hemberger, J.; Croft, M. C.; Walker, D. and Greenblatt, M. Designing Polar and Magnetic Oxides: Zn2 FeTaO6 - in Search of Multiferroics. J. Am. Chem. Soc. 2014, 136, 8508-8511.


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Magnetoelectric Coupling, Ferroelectricity, and Magnetic Memory

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