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.

Mamidanna Sri Ramachandra Rao

Department Of Physics

M. S.Ramachandra Rao

Magnetoelectric couplings

Material systems

POLYCRYSTALLINE BIFEO

Rhombohedral structures

Structural and magnetic properties

WEAK FERROMAGNETIC ORDERING

X-ray diffraction data

X-RAY PHOTOELECTRON SPECTROSCOPY STUDIES

Ceramic materials

Ferromagnetic materials

Ferromagnetism

Iron oxides

Magnetic properties

Photoelectrons

X ray diffraction

X ray photoelectron spectroscopy

calcium

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

Weak ferromagnetic ordering in Ca doped polycrystalline BiFeO3

Journal of Applied Physics

The magnetic properties of Bi1- xCaxFe1- yTiyO3-δ (BCFO: y = 0 and BCFTO: x = y) nanoparticles are studied across a wide range of temperatures (20 K to 960 K) for different Ca (and Ti) concentrations [x (= y) = 0, 0.025, 0.05, and 0.1]. X-ray diffraction and electron microscopy revealed the gradual emergence of the orthorhombic phase (Pnma) with an increase in the Ca2+ content in BCFO, contrary to the retention of parent rhombohedral symmetry (R3c) in Ca2+-Ti4+ co-doped BCFTO. XPS indicates the presence of 3+ valence states for Bi and Fe and under-coordinated defect peaks in O 1s spectra. The ordering of oxygen vacancies in BCFO affects the FeO6 octahedral alignment, resulting in a systematic shift of Fe-O Raman modes. Oxygen vacancies formed due to Ca2+ doping in BCFO and the non-magnetic Ti4+ ion at the Fe3+ site in BCFTO disrupt the spin-cycloid propagation in BiFeO3, largely influencing the magnetic properties. These substitutional changes, in addition to the large surface area, are the sources of net magnetization in these systems. Magnetic hysteresis and field dependent zero field cooled-field cooled curves indicate the combined presence of anti-ferromagnetic and ferromagnetic components in BCFO and BCFTO nanoparticles. High temperature magnetic studies present a clear bifurcation of magnetic Néel transition centered at ∼600 K associated with the structural variation in BCFO. A strong anomaly observed at 860 ± 40 K in all the samples suggests a Hopkinson-like effect arising due to sudden loss of anisotropy by the FM component. © 2018 Author(s).

High temperature magnetic studies on Bi1- xCaxFe1−yTiyO3-δ nanoparticles: Observation of Hopkinson-like effect above TN

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 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.

Applied Physics Letters

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

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.

Chemical pressure effect on optical properties in multiferroic bulk BiFeO 3

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.

Low temperature magnetocaloric effect in polycrystalline BiFeO3 ceramics

Physical Review B

Effect of chemical substitution on the Néel temperature of multiferroicBi1−xCaxFeO3

Nature Materials

Electric modulation of conduction in multiferroic Ca-doped BiFeO3 films

Journal of Alloys and Compounds

Effect of Pb-doping on dielectric properties of BiFeO3 ceramics

Journal	Journal of Applied Physics
ISSN	00218979
Open Access	No