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Showing papers on "Magnetocapacitance published in 2011"


Journal ArticleDOI
TL;DR: The existence of ferroelectricity in NiFe1.925Sm0.075O4 and NiFe 1.925Ho0.0.4 has been confirmed from the ferro electric loops, and the respective transition temperatures are 543 and 677 K.
Abstract: Sm- and Ho-substituted and pure nickel ferrite materials, namely, NiFe1.925Sm0.075O4, NiFe1.925Ho0.075O4, and NiFe2O4, have been synthesized by the solid-state chemical reaction, and their structural, magnetic, dc electrical conductivity, ferromagnetic, ferroelectric, and dielectric properties have been evaluated. Sm- and Ho-substituted nickel ferrites crystallize in the cubic inverse spinel phase with a very small amount of SmFeO3 and HoFeO3 as the additional phase, respectively. X-ray diffraction studies indicate rhombohedral distortion in NiFe1.925Sm0.075O4 and NiFe1.925Ho0.075O4 compounds. The existence of ferroelectricity in NiFe1.925Sm0.075O4 and NiFe1.925Ho0.075O4 has been confirmed from the ferroelectric loops, and the respective transition temperatures are 543 and 677 K. The respective magnetocapacitance values are −1.8% and −1.2%. Magnetoelectric coefficients observed at 500 Oe in the NiFe1.925Sm0.075O4 and NiFe1.925Ho0.075O4 compounds are 1.82 and 1.84 mV cm−1 Oe−1, respectively. A considerable...

158 citations


Journal ArticleDOI
TL;DR: In this article, the linear magnetoelectric effect in antiferromagnetic materials gives rise to a magnetocapacitance anomaly, a divergence of the dielectric constant at the magnetic ordering temperature TN that appears in an applied magnetic field.
Abstract: We give general arguments that show that the linear magnetoelectric effect in antiferromagnetic materials gives rise to a magnetocapacitance anomaly—a divergence of the dielectric constant at the magnetic ordering temperature TN that appears in an applied magnetic field. The measurement of magnetodielectric response thus provides a definitive and experimentally accessible method to recognize antiferromagnetic linear magnetoelectric materials, circumventing the experimental difficulties often involved in measuring electric polarization. We confirm this result experimentally using the example of MnTiO3, which we show to exhibit the linear magnetoelectric effect. No dielectric anomaly is observed at TN in the absence of an applied magnetic field. However, a sharp peak in the dielectric constant appears here when a magnetic field is applied along the c axis, reflecting a linear coupling of the polarization P with the antiferromagnetic order parameter L. In accordance with our theoretical analysis, the dielectric constant close to TN increases with the square of the magnetic field.

80 citations


Journal ArticleDOI
Abstract: BiFe 1− x Cr x O 3 ( x = 0, 004, 006 and 008) nanoceramics were prepared by sol–gel method Nanoceramics were calcined at 450 °C Calcined powders were leached in diluted nitric acid to get single phase TEM analysis shows the particle size to be ∼80 nm Thermogravimetric analysis of as prepared powder indicates that the single phase is formed at around 450 °C Magnetization was found to increase as the concentration of Cr was increased Dielectric constant and dielectric loss were found to decrease with increase in frequency for all the compositions Magnetocapacitance was found to increase with magnetic field For BiFe 1− x Cr x O 3 ( x = 004, 006 and 008) nanoceramics, the change of dielectric constant induced by magnetic field may be well approximated by Δ ɛ / ɛ = γ M 2 , here, γ (magnetoelectric interaction) is small and positive A linear fit gave the value of γ of ∼184 × 10 −2 , 123 × 10 −2 and 33 × 10 −2 for BiFe 1− x Cr x O 3 ( x = 004, 006 and 008) nanoceramics, respectively

77 citations


Journal ArticleDOI
TL;DR: In this article, the structural, magnetic, magnetocapacitance and dielectric properties of BiFe1−xNixO3 nanoceramics were reported by the solgel method.

43 citations


Journal ArticleDOI
TL;DR: In this paper, a detailed study on the colossal dielectric constant and magnetocapacitance of LuFe2O4 was performed, and the experimental results indicate that the large dielectrics constant is originated from two sources, (1) Maxwell Wagner-type contributions of depletion layers at grain boundaries and the interfaces between sample and contacts, (2) AC response of the constant phase element in the bulk.
Abstract: We report the detailed study on the colossal dielectric constant and magnetocapacitance of LuFe2O4. The experimental results indicate that the large dielectric constant of LuFe2O4 is originated from two sources, (1) Maxwell Wagner-type contributions of depletion layers at grain boundaries and the interfaces between sample and contacts, (2) AC response of the constant phase element in the bulk. A detailed equivalent circuit analysis indicates that the conductivity variation can be responsible for the observed “magnetocapacitance.”

43 citations


Journal ArticleDOI
TL;DR: In this paper, the authors describe a non-centrosymmetric space group of multiferroic structures with magnetodielectric properties, with Al 0.5Ga0.5FeO3 showing an unusually large magnetocapacitance at 300 K.
Abstract: AlFeO3, GaFeO3 and Al0.5Ga0.5FeO3, all crystallizing in a non-centrosymmetric space group, are multiferroic and also exhibit magnetodielectric properties, with Al0.5Ga0.5FeO3 showing an unusually large magnetocapacitance at 300 K.

42 citations


Journal ArticleDOI
TL;DR: In this paper, the authors have performed magnetization and magnetocapacitance measurements on ceramic samples of the multiferroic series Bi 1− x La x FeO 3 for 0 ≥ 0.25.
Abstract: We have performed magnetization and magnetocapacitance measurements on ceramic samples of the multiferroic series Bi 1− x La x FeO 3 for 0≤ x ≤.0.25. We show that doping with La reduces the transition magnetic field from the spatially modulated state to a homogenous one and increases the magnetocapacitance, these effects being the strongest for x =0.15, which is the highest concentration for maintaining the non-centrosymmetric rhomboedral structure (R3c) of BiFeO 3 . For highest La content ( x ≥0.17), analysis of the XRD patterns shows that the lattice symmetry gradually changes to orthorhombic (C222), giving rise to an enhancement of the latent magnetization and to a drop of the magnetodielectric constant.

42 citations


Journal ArticleDOI
TL;DR: In this paper, the antiferromagnetic order in the distorted tetrahedral quasi-one-dimensional spin system induces electric polarization, and the effects of low dimensionality and magnetic frustration are expected to appear simultaneously.
Abstract: We clarify that the antiferromagnetic order in the distorted tetrahedral quasi-one-dimensional spin system induces electric polarization. In this system, the effects of low dimensionality and magnetic frustration are expected to appear simultaneously. We obtain the magnetic-field–temperature phase diagram of Cu 3 Mo 2 O 9 by studying the dielectric constant and spontaneous electric polarization. Around the tricritical point at 10 T and 8 K, the change in the direction of electric polarization causes a colossal magnetocapacitance. We calculate the charge redistribution in a small spin cluster consisting of two magnetic tetrahedra to demonstrate the electric polarization induced by the antiferromagnetism.

31 citations


Journal ArticleDOI
TL;DR: In this paper, the mixed spinel-perovskite composites were examined by means of X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM).
Abstract: The mixed spinel–perovskite composites of x MnFe 2 O 4 –(1– x )BiFeO 3 with x =0, 0.1, 0.2, 0.3 and 0.4 were prepared by solid state reaction method. The structure and grain size were examined by means of X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM), respectively. The XRD results showed that the composites consisted of spinel MnFe 2 O 4 and perovskite BiFeO 3 phases after being calcined at the temperature 950 °C for 2 h. The grain size ranged from 0.8 to 1 μm. Magnetization was found to increase with increasing concentration of ferrite content. The variation of dielectric constant and dielectric loss with frequency showed dispersion in the low frequency range. Magnetocapacitance was also observed in the prepared composites, which may be the sign of magnetoelectric coupling in the synthesized composites at room temperature.

27 citations


Journal ArticleDOI
TL;DR: In this article, the antiferromagnetic order in the distorted tetrahedral quasi-one dimensional spin system induces electric polarizations, and the effects of low dimensionality and the magnetic frustration are expected to appear simultaneously.
Abstract: We clarify that the antiferromagnetic order in the distorted tetrahedral quasi-one dimensional spin system induces electric polarizations. In this system, the effects of the low dimensionality and the magnetic frustration are expected to appear simultaneously. We obtain the magnetic-field-temperature phase diagram in Cu3Mo2O9 by studying the dielectric constant and the spontaneous electric polarization. Around the tricritical point at 10 T and 8 K, the change of the direction in the electric polarization causes a colossal magnetocapacitance. We calculate the charge redistribution in the small spin cluster consisting of two magnetic tetrahedra to demonstrate the electric polarization induced by the antiferromagnetism.

26 citations


Journal ArticleDOI
TL;DR: In this paper, a PST/LSMO thin film has been deposited on Si substrate by chemical solution deposition, and anomalous changes in dielectric constant and loss as functions of frequency and magnetic field were observed.
Abstract: Pb0.7Sr0.3TiO3/La0.7Sr0.3MnO3 (PST/LSMO) thin film has been deposited on Si substrate by chemical solution deposition. Obvious changes in dielectric constant and loss as functions of frequency and magnetic field were observed in PST/LSMO thin film. By applying both dc bias electric and magnetic fields, apparent dielectric anomalies were observed in the “butterfly-hysteresis” curves. These effects may be useful for practical application. The mechanism for the magnetocapacitance effects in PST/LSMO is rationalized by combining the Maxwell–Wagner capacitor model and the magnetoresistivity and magnetostriction of the LSMO.

Journal ArticleDOI
TL;DR: In this article, structural, transport, and magnetoelectric properties of delafossite oxides CuCr1−xO2 with 0.10-approximation were investigated and the Rietveld refinement showed that the Cu-O bond length decreases with increasing Cr deficiency.
Abstract: Structural, transport, and magnetoelectric (ME) properties of delafossite oxides CuCr1−xO2 with 0 ≦ x ≦ 0.10 were extensively investigated. The Rietveld refinement shows that the Cu-O bond length decreases with increasing Cr deficiency, indicative of the presence of a mixed valence state of Cu+/Cu2+ and an enhancement of the hybridization between Cu 3d and O 2p orbitals. As a result, it leads to a decrease of room-temperature resistivity by two orders of magnitude. The deduced effective moment for the Cr-deficient samples is larger than the one only taking into account the contribution from Cr3+ with S = 3/2. This demonstrates that Cu2+ is present in the Cr-deficient samples, giving rise to excess holes at the Cu site. Below TN(Cr) ∼ 24 K, the magnetocapacitance [e(H)−e(0)]/e(0) exhibits a distinct field dependence and deviates from the square of magnetization M2. These findings suggest that the ME coupling in CuCr1−xO2 with higher x is modulated by an increase of the spin fluctuations in the CrO2 triangu...

Journal ArticleDOI
TL;DR: The results are interpreted as due not to magnetocapacitance but to the sharp negative magnetoresistance in LSMO at low magnetic fields, which causes a dramatic increase in leakage current through the PZT.
Abstract: We report the strong magnetic field dependence of ferroelectric PbZr0.52Ti0.48O3 (PZT) films on half-metallic oxide La0.67Sr0.33MnO3 (LSMO) electrodes. As the field H is increased, the hysteresis loop first broadens (becomes lossy) and then disappears at approximately H = 0.34?T and ambient temperatures. The data are compared with the theories of Pir? et al (2009 Phys. Rev. B 79 214114), Parish and Littlewood (2008 Phys. Rev. Lett. 101 166602) and Catalan (2006 Appl. Phys. Lett. 88 102902). The results are interpreted as due not to magnetocapacitance but to the sharp negative magnetoresistance in LSMO at low magnetic fields (Hwang et al 1996 Phys. Rev. Lett. 77 2041), which causes a dramatic increase in leakage current through the PZT.

Journal ArticleDOI
Ensi Cao1, Jifan Hu1, Hongwei Qin1, Feng Ji1, Minglei Zhao1, Minhua Jiang1 
TL;DR: In this paper, it was shown that the orthometric application of an electric field and magnetic field on the surface of film leads to an enormous enhancement of in-plane saturation magnetization, indicative of a strong magnetoelectric coupling which has a memory effect on the saturation magnetisation at room temperature.

Journal ArticleDOI
TL;DR: In this article, the giant room-temperature magnetocapacitance was reported in the Terfenol-D/PZT/Terfenol D which is composed of a trilayer structure.
Abstract: The giant room-temperature magnetocapacitance is reported in the Terfenol-D/PZT/Terfenol-D which is composed of a trilayer structure. A giant magnetocapacitance as large as 1200% is observed at the resonant frequency of 52.17 kHz and a saturated magnetic field of 1.5 kOe. We experimentally demonstrate that such magnetocapacitance effect correlates with the frequency shift of harmonic oscillator, i.e., PZT, which resulted from the applied magnetic field. In addition, theoretical analysis shows that the frequency shift is attributed to the product effects of the magnetic field-tuned Young's modulus of the Terfenol-D and the strain-capacitance of the ferroelectrics PZT. One can apply this characteristic of resonance frequency shift to design magnetocapacitance composites with a frequency-tunable magnetic filter.

Journal ArticleDOI
TL;DR: In this paper, a quasi-1D compound, Ca3CoMnO6, has been studied and the magnetodielectric effect (MDE) was found to be positive at 3 K and negative between 3 and 15 K and saturates to a near zero value above 15 K.
Abstract: Magnetocapacitance (MC) measurements—that is, measuring capacitance as a function of temperature at constant magnetic field—has been carried out on a quasi-1D compound, Ca3CoMnO6. MC reveals the presence of a magnetodielectric effect (MDE), which in turn signals the presence of magnetoelectric coupling below the magnetic ordering temperature, TN ( = 15 K). We also observed the sign reversal of the MDE as the temperature increased from 3 to 20 K. The MDE is positive at 3 K and negative between 3 and 15 K, and it saturates to a near zero value above 15 K. The sign change of the MDE is explained in terms the spin-pair correlation of neighboring spins of Co/Mn at a given applied magnetic field H. A negative MDE signifies antiferromagnetic ordering, and a positive MDE signifies ferromagnetic/paramagnetic ordering. Neutron diffraction study reveals changes in the magnetic structure in the temperature range of 2 to 10 K. The present work brings out the possible correlation between the magnetic structure and the ...

Journal ArticleDOI
TL;DR: In this paper, the de Gennes spin order is associated with the formation of canted antiferromagnetic spin order preceded by charge ordering in La 0.5Ba0.5FeO3 synthesized by conventional solid state reaction route.
Abstract: We report multifunctional properties of the charge disproportionate correlated electronic system La0.5Ba0.5FeO3 synthesized by conventional solid state reaction route. The bulk sample undergoes semiconductor–metal like transition at TSM = 102 K showing appreciable magnetoresistance (∼20%) around TSM even at a low field (∼0.5 T). A crossover of electrical conduction mechanism from Mott’s variable range hopping to small polaron hopping occurs around 210 K, well above TSM. Analysis of the transport, magnetic susceptibility, and magnetization data in the light of de Gennes proposal indicates the formation of canted antiferromagnetic spin order preceded by charge ordering in La0.5Ba0.5FeO3. Nonsaturation behavior and nonlinearity of the M-H curve at low temperature and at high field (∼5 T), confirms the canted spin order. The observed resistive transition is considered to be associated with the onset of weak ferromagnetic ordering in the canted antiferromagnetic spin state of the materials. Moreover, novel fer...

Journal ArticleDOI
28 Sep 2011
TL;DR: In this paper, the relationship between the magnetocapacitance effect and rotation direction of electric polarization (P) in a canted magnetic field has been investigated for multiferroic RMnO3 (R = Tb1−xDyx and Eu0.6Y0.4).
Abstract: The relationship between the magnetocapacitance effect and rotation direction of electric polarization (P) in a canted magnetic field has been investigated for multiferroic RMnO3 (R = Tb1−xDyx and Eu0.6Y0.4). We observed a clear correlation between the enhancement of the magnetocapacitance effect and the rotation direction of P in a P-flop transition. These results indicate that the mobility and the stability of the 90° domain wall in a P-flop transition are dominated by its thickness.

Journal ArticleDOI
TL;DR: In this paper, the effect of interface decoration and ac frequency on the magnetoelectric properties of heterojunctions of La 0.5MnO3/SrTiO3:Nb and La0.5Ca0.
Abstract: Effects of interface decoration and ac frequency, under which the impedance is measured, on the magnetoelectric property have been experimentally studied for the heterojunctions of La0.5Ca0.5MnO3/SrTiO3:Nb and La0.5Ca0.5MnO3/LaMnO3(3nm)/SrTiO3:Nb. It is found that the impedance of the junction can be well described by an effective circuit of two R C sub-circuits in series well above 100 K. Magnetocapacitance emerges and develops as temperature decreases, and shows a strong frequency-dependent character. The maximal magnetocapacitance, under a field of 5 T, is similar to 30 and similar to 35% with and without the buffer layer, respectively. The incorporation of the LaMnO3 layer shifts the upper temperature limit for significant rnagnetocapacitance from similar to 120 to similar to 200 K. Shrinkage of the depletion layer of the junction under magnetic field may be a main reason for the magnetoelectric effect observed here. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Proceedings ArticleDOI
27 Dec 2011
TL;DR: In this article, X-ray diffraction (XRD) patterns of powder calcined at 500 0C showed the formation of single-phase rhombohedral structure, which was found to arise from extrinsic effect such as magnetoresistance.
Abstract: Hematite (α-Fe2O3) and 5 mol.% Cr3+ ions doped hematite were synthesized by sol gel method. X-ray diffraction (XRD) patterns of powder calcined at 500 0C show the formation of single-phase rhombohedral structure. Thermogravimetric (TG) analysis of as prepared powder indicates the formation of sample around 400 0C. FESEM analysis shows grain size of sintered pellets ~ 100 nm. Magnetization of hematite powders was found to be higher compared with Cr3+ ions doped hematite at the same magnetic field (10 kOe). We observed magnetocapacitance in both the systems at room temperature. As neither hematite nor Cr3+ ions doped hematite is multiferroic material, the observed magnetodielectric property is believed to arise from extrinsic effect such as magnetoresistance. Keywords—Sol-gel; Magnetic materials; Hematite; X-ray diffraction.

Journal ArticleDOI
TL;DR: In this article, the magnetocapacitance and magnetoresistance of Gd3Ba2Mn2Cu2O12 (Gd-3222) have been measured in the temperature range of 2-300 K.
Abstract: The magnetocapacitance and magnetoresistance of Gd3Ba2Mn2Cu2O12 (Gd-3222) has been measured in the temperature range of 2–300 K. The capacitance increases with increasing temperature from 2–300 K, and exhibits a steplike feature at ∼95 K (for 1 kHz). On increasing the probe frequency this step gets broaden and shifts to higher temperature ∼150 K (for 75 kHz). The observation of frequency dependence in capacitance and dielectric loss (tan δ) exhibits Maxwell–Wagner type relaxor behavior in this compound. Magnetocapacitance was observed on the application of magnetic field. No observable magnetoresistance could be observed in this compound, indicating that the magnetoelectric coupling observed from the dielectric constant measurement with and without magnetic field, is of capacitive origin. The results of magnetocapacitance and magnetoresistance of the Gd-3222 compound are presented in the light of current interest in exploring manganite systems for multiferroic properties.