S. Mollah

Structural, dielectric, and magnetic properties of La0.8Bi0.2Fe1−xMnxO3 (0.0≤x≤0.4) multiferroics

Polycrystalline multiferroic La0.8Bi0.2Fe1−xMnxO3 (0.0≤x≤0.4) samples were synthesized by the conventional solid state reaction method. Reitveld refinement of the x-ray diffraction patterns confirms the single phase character of all the compositions with orthorhombic structure having space group Pnma (No. 62). Dielectric properties of the samples at temperatures 200–475 K and frequencies 500 kHz–1 MHz authenticate the stabilization of ferroelectric phase with Mn substitution. Dielectric responses of these multiferroics have been analyzed carefully, in the light of “universal dielectric response” model. While cooling from room temperature to 20 K, systematic shifts in magnetization hysteresis loops indicate the presence of exchange bias (EB) phenomenon in the system. Magnetic behavior of these samples has been briefly discussed on the basis of “EB” model for granular systems. Temperature and magnetic field dependent magnetization data demonstrate enhanced magnetization due to the Mn substitution. Magnetocapacitance measurement reveals the magnetoelectric coupling for wide range of temperature (180–280 K) and decrease in dielectric loss at high magnetic field (3 T).Polycrystalline multiferroic La0.8Bi0.2Fe1−xMnxO3 (0.0≤x≤0.4) samples were synthesized by the conventional solid state reaction method. Reitveld refinement of the x-ray diffraction patterns confirms the single phase character of all the compositions with orthorhombic structure having space group Pnma (No. 62). Dielectric properties of the samples at temperatures 200–475 K and frequencies 500 kHz–1 MHz authenticate the stabilization of ferroelectric phase with Mn substitution. Dielectric responses of these multiferroics have been analyzed carefully, in the light of “universal dielectric response” model. While cooling from room temperature to 20 K, systematic shifts in magnetization hysteresis loops indicate the presence of exchange bias (EB) phenomenon in the system. Magnetic behavior of these samples has been briefly discussed on the basis of “EB” model for granular systems. Temperature and magnetic field dependent magnetization data demonstrate enhanced magnetization due to the Mn substitution. Magnetoca...

Structural, electrical, magnetic, and electronic structure studies of PrFe1−xNixO3 (x⩽0.5)

We report the x-ray absorption studies on O K, Fe L3,2, Ni L3,2, and Pr M5,4 edges in PrFe1−xNixO3 along with their structural, electrical transport, and magnetization characterizations. All the samples are in single phase having orthorhombic structure with space group Pnma for x⩽0.4. Ni doping at Fe site brings the system in the conducting regime, resistivity decreases from GΩcmto260mΩcm at room temperature, and the magnetic ordering is stabilized. The temperature dependent resistivity follows the semiconducting behavior and fits well with Greaves’ variable range hopping model. The gap parameter is reduced from 2to0.118eV. The materials are in weak ferromagnetic state and magnetization is gradually decreasing with the enhancement of Ni substitution, whereas magnetic anisotropy is reduced substantially. A new feature about 2.0eV lower than the pre-edge of PrFeO3 in O K edge is observed with Ni substitution at Fe site due to the 3d contraction effect and is growing with the increase of Ni substitution. Fro...

Effect of Ti substitution on multiferroic properties of BiMn2O5

We present here the magnetic, dielectric, and electronic structural properties of Ti doped BiMn2O5 multiferroic materials. The x-ray diffraction (XRD) studies of BiMn2−xTixO5 (0≤x≤0.5) indicate no structural change up to x=0.5, though the lattice parameters (a and c) increase with increasing value of x. Dielectric constant and magnetization data show the evolution of new dielectric anomalies at ∼120 K and weak magnetic feature at ∼86 K with the Ti substitution compared to that of undoped one. However, Ti replacement vanishes the ferroelectric transition of BiMn2O5 at ∼35 K and gradually suppresses the antiferromagnetic ordering at ∼39 K. Polarization of Bi 6s2 lone pair electrons is attributed to the reason behind new dielectric anomalies, whereas new weak magnetic feature at ∼86 K is attributed to strong spin-phonon coupling. X-ray absorption spectroscopy (XAS) studies on O K, Mn K, L3,2, and Ti L3,2 edges of BiMn2−xTixO5 samples along with the reference compounds have been performed and compared to best...

NEXAFS studies of La0.8Bi0.2Fe1−xMnxO3(0.0 ⩽ x ⩽ 0.4) multiferroic system using x-ray absorption spectroscopy

We report the electronic structure studies of well-characterized La0.8Bi0.2Fe1−xMnxO3 (LBFM, 0.0 ≤ x ≤ 0.4) multiferroic samples investigated by soft x-ray absorption spectroscopy at O K-, Mn L3,2-, Mn K-, Fe L3,2- and La M4,5-edges along with the spectra of reference compounds. The investigations are performed to find out the chemical states and crystal field symmetry of ions present in the LBFM multiferroic samples after the substitution of Mn ions at Fe sites. Studies reveal a slight shift in the peak positions of O K-edge spectra along with growth in intensities of low-energy features. An analysis of the Mn L3,2- and K-edge, in addition to the comparison with the spectra of reference compounds, indicates that the Mn ions are present in mixed valence states. It is found that the Mn ions are mainly in +3 states along with a small contribution of +2 and +4 ones. The study of Fe L3,2-edge confirms the trivalent state of Fe ion. M4,5-edges of La corroborate the +3 state of La in the system. Atomic multiplet calculations are also performed on Fe L3,2-, Mn L3,2- and La M4,5-edges to further verify the valency, symmetry and the crystal field splitting.

Thin film growth of multiferroic BiMn2O5 using pulsed laser ablation and its characterization

Single phase polycrystalline thin films of multiferroic BiMn2O5 have been prepared on an LaAlO3 (LAO) substrate using the pulsed laser deposition technique. X-ray diffraction and Raman scattering data show that the films are highly strained and have a single phase orthorhombic structure. Near edge x-ray absorption fine structure data of the O K-edge and the Mn L3,2-edge show no change in the electronic structure and the valence state of the BiMn2O5 thin films from that of the bulk. However, magnetic measurements performed over a wide range of temperature (2?300?K) and field (0?2?T) demonstrate a spectacular change in the magnetic behaviour of the BiMn2O5 thin films compared with the bulk. The zero field cooled magnetization confirms the antiferromagnetic transition, similar to the bulk sample, whereas field cooled magnetization data, surprisingly, show spin glass (SG) behaviour. The antiferromagnetic ordering at low temperature (5?K) is confirmed from M?H hysteresis measurements. Atomic force microscopy (AFM) measurement used to study the surface morphology shows unevenly spaced patterns of size ~1?2??m, separated by ridges of peak-to-valley height ~40?nm. The observed magnetic behaviour is explained in the context of the highly strained structure of the films as observed by XRD, Raman scattering and AFM data.

Swift heavy ion irradiation induced magnetism in magnetically frustrated BiMn2O5 thin films

The swift heavy ion (SHI) irradiation induces weak ferrimagnetism (FM) in magnetically frustrated polycrystalline BiMn{sub 2}O{sub 5} thin films. This is manifested from irradiation induced higher energetic configuration that accounts for evolution of the Mn{sup 2+} state in the Mn{sup 3+}/Mn{sup 4+} network. Basically, this is the root of large magnetic moment in the irradiated samples. X-ray diffraction and Raman-scattering data of the samples indicate considerable modifications in the crystal structure after the SHI irradiation. FM in the irradiated samples and magnetically frustrated behavior of the pristine sample is apparent from dc magnetization measurements. Element specific characterizations such as near-edge x-ray absorption fine structure spectroscopy at O K and Mn L{sub 3,2} edges along with x-ray magnetic circular dichroism at Mn L{sub 3,2} edge show the evolution of the Mn{sup 2+} at disbursement of the Mn{sup 4+}. The microscopic origin behind the induced weak FM is found to be the increased orbital moment in the irradiated thin films.

Influence of TiO2 and ZnO on the conductivity and dielectric properties of copper-bismuth glasses

Influence of TiO2 and ZnO oxides has been investigated elaborately on the conductivity and dielectric properties of unconventional and technologically important 40CuO–40Bi2O3–20X (where X=TiO2 and ZnO) glasses. The dc electrical conductivity of ZnO containing glass is found to be higher than that of TiO2 containing one at all temperatures (300–600K). A change from adiabatic to nonadiabatic small polaron hopping conduction is observed due to the influence of TiO2 and ZnO oxides. It has been perceived that the ZnO doped glass shows relatively more ac conductivity compared to that of the TiO2 doped one, consistent with the dc conductivity data. Random-free-energy barrier model of Dyre [J. Appl. Phys. 64, 2456 (1988)] is suited to be the most appropriate one for explaining the frequency dependence of ac conductivity data and frequency exponent. The large dielectric constant in both the glasses can be explained by the response of Bi3+ ions to ac.

Modifications in magnetic properties of BiMn2O5 multiferroic using swift heavy ion irradiation

We report the near edge x-ray absorption fine structure (NEXAFS) and x-ray magnetic circular dichroism (XMCD) studies at the Mn L3,2 edge of pulsed laser deposited pristine thin films of multiferroic BiMn2O5. These investigations are furthermore testified for BiMn2O5 thin films irradiated through 200 MeV Ag15+ ions with fluence value 5×1011 ions/cm2. Though the pristine film is primarily antiferromagnetic in nature, irradiation induces ferrimagnetism in it. Element specific characterizations, NEXAFS and XMCD demonstrate the evolution of Mn2+ state piloting to magnetic signal associated with it.

Inspection of multiferroicity in BiMn2 − xTixO5 ceramics through specific heat and Raman spectroscopic studies

Inspection of multiferroicity in BiMn(2 - x)Ti(x)O(5) (0 ≤ x ≤ 0.30) (BMTO) ceramics is performed through specific heat and Raman spectroscopic studies. Thermal variation of specific heat (C) (in the absence and presence of fixed magnetic fields up to 14 T) and Raman spectra of BMTO are presented. In the temperature variation of C, a remarkable anomaly at the antiferromagnetic (AFM) ordering temperature (T(N) ∼ 39 K) is observed in all samples. Pure BiMn(2)O(5) (for x = 0.0) exhibits a larger specific heat anomaly at T(N) compared to that of Ti substituted samples, both in the presence and absence of external magnetic fields. The excess specific heat (ΔC) versus T clearly illustrates appreciable anomalies at ∼ 86 and ∼ 120 K in Ti doped samples related to the magnetic and dielectric transitions, respectively. The low temperature specific heat (LTSH) data indicate a considerably improved ferromagnetic contribution in samples with higher Ti concentration (x > 0.15). The Raman spectra of the doped samples at different fixed temperatures validate the strong electron-phonon coupling corresponding to the observed magnetism and increased harmonicity at dielectric transitions.