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. © 2009 American Institute of Physics.

Mamidanna Sri Ramachandra Rao

Department Of Physics

M. S. Ramachandra Rao

Coercive field

LOW TEMPERATURE PHASE TRANSITIONS

Low temperatures

Magnetic entropy change

Magneto-caloric effects

Polycrystalline

Powder X ray diffraction

Relative errors

Rhombohedral structures

SOL-GEL ROUTES

SPACE GROUP R3C

Ceramic materials

Magnetic properties

Phase Transitions

Rare earth alloys

Sol-gel process

X ray diffraction

Thermal effects

Fulltext

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Low temperature magnetocaloric effect in polycrystalline BiFeO3 ceramics

Applied Physics Letters

Temperature-dependent thermal conductivity of polycrystalline BiFeO3, Bi0.9Ba0.05Ca0.05FeO2.95 and Bi0.9Ca0.1FeO2.95 materials was measured using a direct heat pulse technique. Thermal conductivity of the BiFeO3-based materials is analyzed using a phonon model to probe the thermal transport mechanisms in these ferrites. It is found that the calculated thermal conductivity of the BiFeO3-based compounds is in good agreement with experimental data. The suppression of the low-temperature phonon peak in the thermal conductivity of the doped BiFeO3 materials is mainly attributed to the phonon-point-defect scattering. In addition, the contribution of optical phonon-magnon resonance scattering to optical phonon thermal transport reveals the presence of phonon-magnon coupling in these BiFeO3 materials. Finally, magneto-thermal conductivity measurements show the magnon thermal transport in pure and doped BiFeO3 systems. © 2015 IOP Publishing Ltd.

Journal of Physics D: Applied Physics

Phonon thermal transport and phonon-magnon coupling in polycrystalline BiFeO3 systems

We studied magnetic properties of bulk LaCrO3; a GdFeO3-type distorted perovskite, with a predominant antiferromagnetic phase transition at ∼290 K. The bulk LaCrO3 exhibits intrinsic weak ferro magnetism at room temperature, which may arise due to the tilting of CrO6 octahedra, resulting in a non-zero net magnetic moment, as confirmed from the magnetization measurements. A broad magnetically-induced entropy change (-ΔS) is observed with the maxima at 290 K, close to room temperature in LaCrO3 system. © 2015 IOP Publishing Ltd.

Materials Research Express

Magnetostructural and magnetocaloric properties of bulk LaCrO3 system

We have investigated temperature, frequency, and magnetic field dependent dielectric properties of polycrystalline Bi 0.9Ca 0.1FeO 2.95. Two dielectric anomalies, near 65 K and 260 K, were observed with the anomaly near 65 K exhibiting distinct frequency dependence as the peak temperature shifts with increasing frequency. The low-temperature dielectric relaxation data that can be fitted to a Vogel-Fulcher expression yielding a characteristic relaxation time of ∼10 -8 s are four orders larger than that of pure BiFeO 3 which may be the resultant of the chemical pressure induced by Ca doping. We also observed a switchable magneto-dielectric response in Bi 0.9Ca 0.1FeO 2.95 at room temperature. © 2012 American Institute of Physics.

Dielectric relaxation and magneto-dielectric effect in polycrystalline Bi 0.9Ca 0.1FeO 2.95

Structural and magnetic properties of polycrystalline BiFeO3, Bi0.9Ca0.1FeO2.95, Bi0.9Ba 0.05Ca0.05 FeO2.95, and Bi0.9Ba 0.1FeO2.95 ceramic samples were studied to establish the effects of doping in BiFeO3 on the magnetic property. X-ray diffraction data of the undoped and doped BiFeO3 samples were refined to a rhombohedral structure with space group R3c. X-ray photoelectron spectroscopy study showed the formation of a single-phase in both the undoped and doped BiFeO3 ceramics with Fe in the 3 valence state. Ca doped and Ba-Ca co-doped BiFeO3 ceramic samples show weak ferromagnetic ordering at room temperature. This observation makes Ca doped and Ba-Ca co-doped BiFeO3 samples an interesting material system for magnetoelectric coupling studies. © 2012 American Institute of Physics.

Journal of Applied Physics

Weak ferromagnetic ordering in Ca doped polycrystalline BiFeO3

We have investigated diffuse reflectance spectra of the polycrystalline BiFeO 3, Bi 0.9Ba 0.05Ca 0.05FeO 2.95, and Bi 0.9Ca 0.1FeO 2.95 samples to demonstrate crystal-field spectroscopy, which enabled us to explore local distortion in the non-centrosymmetric FeO 6 octahedron, and also to study chemical pressure effect on the band gap and d-d transition band energies. The energy values of band gap and d-d transition bands of the doped BiFeO 3 samples were found to red-shift with the reduced unit cell volume. Absorption spectroscopic studies of the BiFeO 3 samples reveal that nature of the band gap is a direct. Raman spectroscopy study also reveals that the softening/hardening of the certain Raman modes in BiFeO 3 upon substitution of Ca. The chemical pressure induced changes in the band gap and d-d band energies, and the Raman modes of the Ca doped BiFeO 3, which also found to enhance its magnetic and magnetoelectric properties. © 2012 American Institute of Physics.

Journal	Applied Physics Letters
ISSN	00036951
Open Access	No