Journal ArticleDOI

# Low temperature magnetocaloric effect in polycrystalline BiFeO3 ceramics

07 Oct 2009-Applied Physics Letters (American Institute of Physics)-Vol. 95, Iss: 14, pp 142505

Abstract: We report on the structural, thermal, and magnetic properties of polycrystalline BiFeO3 synthesized by sol-gel route. Powder x-ray diffraction data of the BiFeO3 sample was refined with rhombohedral structure with space group R3c. Magnetization and coercive field measurements showed weak ferromagnetic nature below 10 K. We also investigated the low temperature magnetocaloric effect in polycrystalline BiFeO3 ceramics. The anomalies observed in the magnetic entropy change of the BiFeO3 ceramics were close to that of low temperature phase transitions. The combined relative errors in the magnetic entropy change are found to vary from 4% to 15% with increase in temperature.
Topics: Magnetization (56%), Coercivity (55%), Magnetic refrigeration (54%), Ferromagnetism (53%)
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Zhonghua Dai1, Yukikuni Akishige1Institutions (1)
Abstract: Single-phase multiferroic BiFeO3 powder was prepared by improved solid-state synthesis, and dense BiFeO3 ceramics were fabricated by a spark plasma sintering (SPS) process. The sintering temperature of SPS ranged from 650 to 800 °C under 50 MPa. It is found that the sample is not only single phased but also of high density when sintered at 650 °C. The dielectric constant and loss of the samples were tested between 100 Hz and 20 MHz at several temperatures. Oxygen and vacuum annealing conditions impact the dielectric behaviour of the BiFeO3 ceramics prepared by the SPS technique obviously. The piezoelectric coefficient d33 of the sample annealed in vacuum is 4.2 pC N−1 at room temperature.

131 citations

Journal ArticleDOI
B. Ramachandran1, Ambesh Dixit2, R. Naik2, Gavin Lawes2  +1 moreInstitutions (2)
Abstract: We report on the electronic energy-level diagram of polycrystalline ${\text{BiFeO}}_{3}$ using the elemental, optical, and current-density-electric field $(J\text{\ensuremath{-}}E)$ characteristics. The elemental, electronic composition, and valence-band structure of ${\text{BiFeO}}_{3}$ ceramics were studied using x-ray photoelectron spectroscopy. The diffuse reflectance spectrum of a mixture of ${\text{BiFeO}}_{3}$ and ${\text{BaSO}}_{4}$, used as a standard, was recorded to test the Kubelka-Munk model. From the graph of the Kubelka-Munk function versus wavelength, two charge-transfer bands and two doubly degenerated $d\text{\ensuremath{-}}d$ transitions (${^{6}\text{A}}_{1\text{g}}\ensuremath{\rightarrow}{^{4}\text{T}}_{2\text{g}}$ and ${^{6}\text{A}}_{1\text{g}}\ensuremath{\rightarrow}{^{4}\text{T}}_{1\text{g}}$) were observed in polycrystalline ${\text{BiFeO}}_{3}$. The $J\text{\ensuremath{-}}E$ curves measured on the ${\text{BiFeO}}_{3}$ ceramics showed space-charge-limited conduction mechanism.

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Journal ArticleDOI
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Journal ArticleDOI
Dawei Wang1, Dawei Wang2, Meili Wang1, Fengbin Liu1  +5 moreInstitutions (4)
Abstract: Neodymium doped bismuth ferrite (BiFeO3, BFO) nanoparticles were successfully synthesized by a facile sol–gel route. The influence of annealing temperature, time, Bi content and solvent on the crystal structure of BFO was studied. Results indicated that the optimum processing condition of BFO products was 550–600 1C/1.5 h with excess 3–6% Bi and ethylene glycol as solvent. On the other hand, Nd 3 þ ion was introduced into the BFO system and the effect of Nd 3 þ concentration on the structure, magnetic and dielectric properties of BFO were investigated. It was found that the magnetization of BFO was enhanced significantly with Nd 3 þ substitution, being attributed to the suppression of the spiral cycloidal magnetic structure led by the crystal structure transition. Furthermore, with increasing Nd 3 þ content, the dielectric constant was found to decrease while the dielectric loss was enhanced, which was mainly due to the hoping conduction mechanism with the reduction of oxygen vacancies. & 2015 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

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Journal ArticleDOI
Abstract: Polycrystalline GaFeO 3 prepared by a solid state (SR) and a sol–gel (SG) procedure crystallize in the orthorhombic system with space group Pc 2 1 n . Neutron powder diffraction revealed iron ions fractions over the four sites Ga1, Ga2, Fe1 and Fe2: (0.2, 0.55, 0.70, 0.55) and (0.04, 0.75, 0.51, 0.72) for GaFeO 3 (SR) and GaFeO 3 (SG), respectively. The Curie temperature ( T C ) for GaFeO 3 (SR) is about 190 K and increases to room temperature when the temperature of annealing is decreased from 1400 to 900 °C. The dielectric constant and dielectric loss are temperature and frequency independent for both samples. Below the transition temperature, T C , a ferrimagnetic order with a propagation vector k = 0 was derived from neutron powder diffraction data. The Fe 3+ magnetic moments are ordered along the c -axis with a small component along a and b . At 3 K, the magnetic moments of Fe 3+ are 3.47(9) and 4.40(1) μ B for GaFeO 3 (SR) and GaFeO 3 (SG), respectively. Both, the cation and magnetic ordering depend strongly on the preparation conditions.

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##### References
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Journal ArticleDOI
Jian Wang1, Jeffrey B. Neaton2, Haimei Zheng1, Valanoor Nagarajan1  +10 moreInstitutions (5)
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TL;DR: Enhanced polarization and related properties in heteroepitaxially constrained thin films of the ferroelectromagnet, BiFeO3, and combined functional responses in thin film form present an opportunity to create and implement thin film devices that actively couple the magnetic and ferroelectric order parameters.
Abstract: Enhancement of polarization and related properties in heteroepitaxially constrained thin films of the ferroelectromagnet, BiFeO3, is reported. Structure analysis indicates that the crystal structure of film is monoclinic in contrast to bulk, which is rhombohedral. The films display a room-temperature spontaneous polarization (50 to 60 microcoulombs per square centimeter) almost an order of magnitude higher than that of the bulk (6.1 microcoulombs per square centimeter). The observed enhancement is corroborated by first-principles calculations and found to originate from a high sensitivity of the polarization to small changes in lattice parameters. The films also exhibit enhanced thickness-dependent magnetism compared with the bulk. These enhanced and combined functional responses in thin film form present an opportunity to create and implement thin film devices that actively couple the magnetic and ferroelectric order parameters.

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Journal ArticleDOI
24 Oct 2002-Nature
TL;DR: Spatial maps of coupled antiferromagnetic and ferroelectric domains in YMnO3 are obtained by imaging with optical second harmonic generation and lead to a configuration that is dominated by the ferroelectromagnetic product of the order parameters.
Abstract: Ferroelectromagnets are an interesting group of compounds that complement purely (anti-)ferroelectric or (anti-)ferromagnetic materials--they display simultaneous electric and magnetic order. With this coexistence they supplement materials in which magnetization can be induced by an electric field and electrical polarization by a magnetic field, a property which is termed the magnetoelectric effect. Aside from its fundamental importance, the mutual control of electric and magnetic properties is of significant interest for applications in magnetic storage media and 'spintronics'. The coupled electric and magnetic ordering in ferroelectromagnets is accompanied by the formation of domains and domain walls. However, such a cross-correlation between magnetic and electric domains has so far not been observed. Here we report spatial maps of coupled antiferromagnetic and ferroelectric domains in YMnO3, obtained by imaging with optical second harmonic generation. The coupling originates from an interaction between magnetic and electric domain walls, which leads to a configuration that is dominated by the ferroelectromagnetic product of the order parameters.

1,278 citations

Journal ArticleDOI
01 Jul 1982

964 citations

Journal ArticleDOI
Abstract: The temperature dependence of structural and magnetic order parameters of ferroelectric-antiferromagnetic BiFeO3 with rhombohedral perovskite structure is investigated by means of neutron diffraction on a powder sample. The tilt angle of oxygen octahedra decreases from 12.5 degrees at 4.2K to 11.4 degrees at 878K. Associated with ferroelectricity the cation displacements diminish essentially with increasing temperature. Changes of cation shifts, tilt angle, distortion and strain of octahedra are discussed with respect to phase transitions.

860 citations

Journal ArticleDOI
Abstract: Single crystals of BiFeO3 of perovskite structure were grown with dimensions of greater than 1 mm from a Bi2O3 flux. Dielectric hysteresis loops were measured on these crystals. While the loops were not fully saturated, they confirm that BiFeO3 is ferroelectric.

799 citations

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