arXiv subjects

R. N. Bhowmik

Publications and source records attributed to R. N. Bhowmik.

At least 19 recordsLinked to original sources

arXiv2026

Role of lattice structure and breaking of antiferromagnetic spin order in enhancement of ferromagnetic, electronic, and magneto-electric properties in Fe$_{2-x}$Sc$_x$O$_3$ system

The strategy of breaking antiferromagnetic (AFM) ground state in alpha-Fe2O3 by doping non-magnetic Sc3+ ions at the Fe3+ sites has been used in Fe2-xScxO3 system (x = 0.2-1.0). The material has been stabilized in single-phase (rhombohedral alpha-Fe2O3) or mix-phase (rhombohedral alpha-Fe2O3 and cubic Sc2O3-types) structure by varying Sc content and heat treatment temperature. Neutron diffraction confirmed perturbed AFM ground state down to low temperature with magnetic moment 2.75-4.68 muB per Fe site and Morin transition 260 K. DC magnetic measurement showed magnetic coercivity 0.2 to 6 kOe. The material showed transformation from insulating state (conductivity 10-14-10-10 S per cm and polarization 0.5-2 micro-C per cm2) to high conductive state (conductivity 10-10 -10-7 S per cm and polarization greater than 2 micro-C per cm2) above the Morin transition. The room temperature measurements showed maximum current density 35-186 micro-A per cm2, electric polarization 2.7-15.6 micro-C per cm2, magneto-electric voltage up to 5 mV with coupling constant 0.62-10.11 mV per Oe.cm and magneto-conductance up to 90 %. The results will open the door for suitably modifying the lattice-structure, magnetic spin order, and charge-spin coupling in hematite based material and their application in low power spintronic devices.

cond-mat.mtrl-sci↗

arXiv2022

Bulk superconductivity and non-trivial band topology analysis of Pb2Pd

A perfect topological superconductor can be realized by the simultaneous existence of bulk superconductivity along with topological non-trivial surface states. In this article, we report single crystal growth of superconducting binary compound Pb2Pd. The crystal is well characterized through X-Ray Diffraction (XRD), Selected Area electron diffraction (SAED), Transmission Electron Microscopy (TEM), Field emission Scanning electron Microscopy (FESEM) and X-Ray Photoelectron spectroscopy (XPS). The bulk superconducting nature of the studied crystal is determined through AC susceptibility and magneto-heat capacity measurements. The specific heat jump at superconducting transition suggests Pb2Pd to be a moderately coupled s-wave superconductor. The topological non-trivial character of Pb2Pd is evidenced through bulk electronic band structure and Z2 invariants, which are calculated under the protocols of Density Functional Theory (DFT). This is the first report on topological invariant of Pb2Pd, showing Pb2Pd to possess non-trivial topological band structure

cond-mat.supr-con↗

arXiv2020

Probing low temperature non-equilibrium magnetic state in Co$_{2.75}$Fe$_{0.25}$O$_{4+δ}$ spinel oxide using dc magnetization, ac susceptibility and neutron diffraction experiments

The low temperature lattice structure and magnetic properties of Co$_{2.75}$Fe$_{0.25}$O$_4$ ferrite have been investigated using experimental results from synchrotron x-ray diffraction (SXRD), dc magnetization, ac susceptibility, neutron diffraction and neutron depolarization techniques. The samples have been prepared by chemical co-precipitation of the Fe and Co nitrates solution in high alkaline medium and subsequent thermal annealing of the precipitates in the temperature range of 200- 900 $^\circ$C. Rietveld refinement of the SXRD patterns at room temperature indicated two-phased cubic spinel structure for the samples annealed at temperatures 200-600 $^\circ$C. The samples annealed at temperatures 700 $^\circ$C and 900 $^\circ$C (CF90) have been best fitted with single phased lattice structure. Refinement of the neutron diffraction patterns in the temperature range of 5-300 K confirmed antiferromagnetic (AFM) Co$_3$O$_4$ and ferrimagnetic (FIM) Co$_{2.75}$Fe$_{0.25}$O$_4$ phases for the sample annealed at 600 $^\circ$C and single FIM phase of Co$_{2.75}$Fe$_{0.25}$O$_4$ for the CF90 sample. Magnetic measurements have shown a non-equilibrium magnetic structure, consisting of the high temperature FIM phase and low temperature AFM phase. The magnetic phases are sensitive to magnetic fields, where high temperature phase is suppressed at higher magnetic fields by enhancing the low temperature AFM phase, irrespective of annealing temperature of the samples.

cond-mat.str-el↗

arXiv2020

Non-equilibrium spin dynamics in the temperature and magnetic field dependence of magnetization curves of ferrimagnetic Co$_{1.75}$Fe$_{1.25}$O$_4$ and its composite with BaTiO$_3$

A comparative study of the non-equilibrium magnetic phenomena (magnetic blocking, memory, exchange bias and aging effect) has been presented for ferrimagnetic Co$_{1.75}$Fe$_{1.25}$O$_4$ (CFO) and its composite with non-magnetic BaTiO$_3$ (BTO). Synchrotron X-Ray diffraction patterns have confirmed coexistence of CFO and BTO structures in composite, but magnetic spin dynamics have been remarkably modified. The blocking phenomenon of ferrimagnetic domains below the room temperature has been studied by different modes of (zero field cooled and field cooled) magnetic measurements in collaboration with magnetic fields ON and OFF modes and time dependent magnetization. The applications of unconventional protocols during time dependent magnetization measurement at different stages of the temperature and field dependence of the magnetization curves have been useful to reveal the non-equilibrium dynamics of magnetic spin order. The applying of off-field relaxation experiments has made possible to tune the magnetic state and coercivity of the systems. The role of interfacial coupling between magnetic and non-magnetic particles has been understood on different magnetic phenomena (meta-stable magnetic state, exchange bias and memory effect) by comparing the experimental results of Co$_{1.75}$Fe$_{1.25}$O$_4$ spinel oxide and its composite with BaTiO$_3$ particles.

cond-mat.mtrl-sci↗

arXiv2020

High temperature thermal cycling effect on the irreversible responses of lattice structure, magnetic properties and electrical conductivity in Co$_{2.75}$Fe$_{0.25}$O$_{4+δ}$ spinel oxide

We report high temperature synchrotron X-ray diffraction (SXRD), dc magnetization and current-voltage (I-V) characteristics for the samples of Co$_{2.75}$Fe$_{0.25}$O$_4$ ferrite. The material was prepared by chemical reaction of the Fe and Co nitrate solutions at pH = 11 and subsequent annealing at temperatures 200 0C, 500 0C and 900 0C. The measurements were performed by cycling the temperature from 300 K to high temperature (warming mode) and return back to 300 K (cooling mode). The SXRD patterns indicated a fine bi-phased cubic spinel structure in the highly Co rich spinel oxide. Magnetization curves showed intrinsic ferrimagnetic features and defect induced additional ferromagnetic phase at higher temperatures. Electrical conductivity showed thermal hysteresis loop between warming and cooling modes of temperature variation. The samples exhibited new information on the irreversibility phenomena of lattice structure, magnetization and electrical conductivity on cycling the measurement temperatures.

cond-mat.mtrl-sci↗

arXiv2020

Tuning of structural phase, magnetic spin order and electrical conductivity in mechanical alloyed material of alpha-Fe2O3 and alpha-Cr2O3 oxides

Alpha-Fe2O3 and alpha-Cr2O3 has been mechanical alloyed to prepare Fe1-xCrxO3 oxides for x = 0.2-0.8. Synchrotron X-ray diffraction and Raman spectra have shown inhomogeneous structure of α-Fe2O3 and α-Cr2O3 phases in as-alloyed samples. The as-alloyed samples have shown soft ferromagnetic properties with signature of two Morin transitions. The heat treatment of as-alloyed samples has homogenized structure and successfully incorporated the Cr atoms into the lattice sites of Fe atoms in α-Fe2O3. The magnetic and electrical properties have been modified in the heat treated samples. For example, canted antiferromagnetic order has been appeared as an effect of heat treatment, irrespective of the Cr content in Fe1-xCrxO3. The magnetic field induced spin flop transition has been observed at a critical magnetic field that depends on Cr content in the system. The Mössbauer spectrum at room temperature has been fitted with two sextets. The variation of Mössbauer parameters suggest a distribution of magnetic spin order between Fe and Cr ions in the rhombohedral structure of Fe1-xCrxO3. The electrical conductivity, derived from current-voltage characteristics of the heat treated samples, has been enhanced by increasing Cr content in alpha-Fe2O3 structure. The experimental results have been explained based on the theoretical models available in literature.

cond-mat.mtrl-sci↗

arXiv2019

Physical properties of RIr3 (R = Gd, Tb, Ho) compounds with coexisting polymorphic phases

The binary compounds GdIr3, TbIr3 and HoIr3 are synthesized successfully and found to form in macroscopic co-existence of two polymorphic phases: C15b and AuCu3-type. The dc magnetization and heat capacity studies confirm that C15b phase orders ferromagnetically, whereas the AuCu3 phase remains paramagnetic down to 2 K. The frequency dependent ac-susceptibility data, time dependent magnetic relaxation behavior and magnetic memory effect studies suggest that TbIr3 and HoIr3 are cannonical spin-glass system, but no glassy feature could be found in GdIr3. The critical behavior of all the three compounds has been investigated from the magnetization and heat capacity measurements around the transition temperature (TC). The critical exponents alpha, beta, gamma and delta have been estimated using different techniques such as Arrott-Noaks plot, Kouvel-Fisher plot, critical isotherm as well as analysis of specific heat data and study of magnetocaloric effect. The critical analysis study identifies the type of universal magnetic class in which the three compounds belong.

cond-mat.mtrl-sci↗

arXiv2017

Low temperature ferromagnetic properties, magnetic field induced spin order and random spin freezing effect in Ni1.5Fe1.5O4 ferrite; prepared at different pH values and annealing temperatures

We present the low temperature magnetic properties in Ni1.5Fe1.5O4 ferrite as the function of pH at which the material was prepared by chemical route and post annealing temperature. The material is a ferri or ferromagnet, but showed magnetic blocking and random spin freezing process on lowering the measurement temperature down to 5 K. The sample prepared at pH =12 and annealed at 800 ^C showed a sharp magnetization peak at 105 K, the superparamagnetic blocking temperature of the particles. The magnetization peak remained incomplete within measurement temperature up to 350 K for rest of the samples, although peak temperature was brought down by increasing applied dc field. The fitting of temperature dependence of coercivity data according to Kneller law suggested random orientation of ferromagnetic particles. The fitting of saturation magnetization according to Bloch law provided the exponent that largely deviated from 1.5, a typical value for long ranged ferromagnet. An abrupt increase of saturation magnetization below 50 K suggested the active role of frozen surface spins in low temperature magnetic properties. AC susceptibility data elucidated the low temperature spin freezing dynamics and exhibited the characters of cluster spin glass in the samples depending on pH value and annealing temperature.

cond-mat.mtrl-sci↗

arXiv2017

Effect of annealing temperatures on the electrical conductivity and dielectric properties of Ni1.5Fe1.5O4 spinel ferrite prepared by chemical reaction at different pH values

The electrical conductivity and dielectric properties of Ni1.5Fe1.5O4 ferrite has been controlled by varying the annealing temperature of the chemical routed samples. The frequency activated conductivity obeyed Jonschers power law and universal scaling suggested semiconductor nature. An unusual metal like state has been revealed in the measurement temperature scale in between two semiconductor states with different activation energy. The metal like state has been affected by thermal annealing of the material. The analysis of electrical impedance and modulus spectra has confirmed non-Debye dielectric relaxation with contributions from grains and grain boundaries. The dielectric relaxation process is thermally activated in terms of measurement temperature and annealing temperature of the samples. The hole hopping process, due to presence of Ni3+ ions in the present Ni rich ferrite, played a significant role in determining the thermal activated conduction mechanism. This work has successfully applied the technique of a combined variation of annealing temperature and pH value during chemical reaction for tuning electrical parameters in a wide range; for example dc limit of conductivity 10power(-4) -10power(-12) S/cm, and unusually high activation energy 0.17-1.36 eV.

cond-mat.mtrl-sci↗

arXiv2017

Non-equilibrium character of resistive switching and negative differential resistance in Ga-doped Cr2O3 system

We have synthesized Ga-doped Cr2O3 system with compositions Cr1.45Ga0.55O3 and Cr1.17Ga0.83O3 by chemical co-precipitation route and post annealing at 800^C. The samples have been stabilized in rhombohedral crystal structure with space group R3C. The present work focuses on the study of non-linear current-voltage (I-V) characteristics of the samples, which exhibited many interesting electronic properties, e.g., I-V loop, resistive switching, bi-stable electronic states, and negative differential resistance. The non-equilibrium character of the I-V characteristics has been studied by measurement of bias voltage cycling up to 20 times and current relaxation with time at set bias voltage. The charge conduction process in the samples has been understood by analysing I-V curves using different phenomenological models based on electrode-limited and bulk-limited charge conduction mechanisms proposed for metal electrode-metal oxide-metal electrode (M-MO-M) junctions. It is understood that competitions between injection of charge carriers from metal electrode to metal oxide, charge flow through the material (trapping/de-trapping and recombination of charge carriers at the defect sites), space charge formation at the junctions of electrodes and metal oxides, and ejection of electrons from metal oxide to metal electrode control the non-equilibrium I-V characteristics in the present samples.

cond-mat.mtrl-sci↗

arXiv2017

Electric field controlled magnetic exchange bias and magnetic state switching at room temperature in Ga doped α-Fe2O3 oxide

We have developed a new magnetoelectric material based on Ga doped α-Fe2O3 in rhombohedral phase. The material is a canted ferromagnet at room temperature and showing magneto-electric properties. The experimental results of electric field controlled magnetic state provided a direct evidence of room temperature magnetoelectric coupling in Ga doped α-Fe2O3 system. Interestingly, (un-doped) α-Fe2O3 system does not exhibit any electric field controlled magnetic exchange bias shift, but Ga doped α-Fe2O3 system has shown an extremely high electric field induced magnetic exchange bias shift up to the value of 1120 Oe (positive). On the other hand, in a first time, we report the electric field controlled magnetic state switching both in α-Fe2O3 and in Ga doped α-Fe2O3 systems. The switching of magnetic state is highly sensitive to ON and OFF modes, as well as to the change of polarity of applied electric voltage during in-field magnetic relaxation experiments. The switching of magnetic state to upper level for positive electric field and to down level for negative electric field indicates that electric and magnetic orders are coupled in the Ga doped hematite system. Such material is of increasing demand in today for multifunctional applications in next generation magnetic sensor, switching, non-volatile memory and spintronic devices.

cond-mat.mtrl-sci↗

arXiv2016

Evidence of room temperature magnetoelectric properties in α-Fe1.6Ga0.4O3 oxide by magnetic field controlled electric properties and electric field controlled magnetism

We have stabilized the α-Fe1.6Ga0.4O3 (Ga doped α-Fe2O3) system in rhombohedral structure. The system has shown magnetically canted ferromagnetic state and ferroelectric properties at room temperature. In first time, we confirm the existence of magneto-electric coupling and multiferro-electric properties at room temperature in the Ga doped α-Fe2O3 system based on the experimental observation of magnetic field controlled electric polarization and electric field controlled magnetization. The α-Fe2O3 system does not exhibit electric field controlled magnetic exchange bias effect, where as Ga doped α-Fe2O3 showed exchange bias shift up to the value of 370 Oe. We have recorded the response of current-voltage characteristics and in-field magnetic relaxation of the system under the simultaneous application of magnetic and electric fields. The magnetization of the system is found highly sensitive to the ON and OFF modes, as well as change of the polarity of external electric field. The system is a new addition in the list of non-traditional magneto-electrics/multi-ferroelectrics so far reported in literature. Such novel materials, where magnetization and electric polarization can be controlled by simultaneous application of magnetic and electric fields, is in the increasing demand for potential applications in the field of next generation magnetic sensor, switching, non-volatile memory and spintronic devices.

cond-mat.mtrl-sci↗

arXiv2016

Doping of Ga in antiferromagnetic semiconductor alpha-Cr2O3oxide and its effects on modified magnetic and electronic properties

The samples of Ga doped Cr2O3 oxide have been prepared using chemical co-precipitation route. X-ray diffraction pattern and Raman spectra have confirmed rhombohedral crystal structure with space group R3-C. Magnetic measurement has indicated the dilution of antiferromagnetic (AFM) spin order in Ga doped alpha-Cr2O3 system oxide, where the AFM transition temperature of bulk alpha-Cr2O3 oxide at about 320 K has been suppressed and ferrimagnetic behavior is observed from the analysis of the temperature dependence of magnetization data below 350 K. Apart from Ga doping effect, the spin freezing (50 K-70 K) and superparamagnetic behavior of the surface spins at lower temperatures, typically below 50 K, have been exhibited due to nano-sized grains of the samples. All the samples showed non-linear current-voltage (I-V) characteristics. However, I-V characteristics of the Ga doped samples are remarkably different from alpha-Cr2O3 sample. The I-V curves of Ga doped samples have exhibited many unique electronic properties, e.g., bi-stable (low resistance- LR and high resistance-HR) electronic states and negative differential resistance (NDR). Optical absorption spectra revealed three electronic transitions in the samples associated with band gap energy at about 2.67-2.81 eV, 1.91-2.11 eV, 1.28-1.35 eV, respectively.

cond-mat.mtrl-sci↗

arXiv2013

Observation of plastoferrite character and semiconductor to metal transition in soft ferromagnetic Li0.5Mn0.5Fe2O4ferrite

We prepared Li0.5Mn0.5Fe2O4 ferrite through chemical reaction in highly acidic solution and subsequent sintering of chemical routed powder at temperatures > 800 0C. Surface morphology showed plastoferrite character for sintering temperature > 1000 0C. Mechanical softening of metal-oxygen bonds at higher measurement temperatures stimulated delocalization of charge carriers, which were strongly localized in A and B sites of the spinel structure at lower temperatures. The charge delocalization process has activated semiconductor to metallic transition in ac conductivity curves, obeyed by Jonscher power law and Drude equation, respectively. Metallic state is also confirmed by the frequency dependence of dielectric constant curves.

cond-mat.mtrl-sci↗

arXiv2013

Low temperature ferromagnetism, surface paramagnetism and exchange bias effect in nano-grained alpha-Fe1.4Ga0.6O3 oxide

The compound alpha-Fe1.4Ga0.6O3 has been prepared by mechanical alloying of alpha-Fe2O3 and Ga2O3 and subsequent heating of the mechanical alloyed samples in vacuum condition. Magnetic ordering of alpha-Fe2O3 has been modified by substitution of non-magnetic Ga atoms. The ferromagnetism in alpha-Fe1.4Ga0.6O3 is more soft and enhanced in comparison to alpha-Fe2O3. Mössbauer spectroscopy also confirmed enhanced ferromagnetic order in alpha-Fe1.4Ga0.6O3. The room temperature soft ferromagnetism by Ga substitution is interesting for designing alpha-Fe2O3 based unconventional ferromagnet, which is a great challenge to the materials scientists. The alpha-Fe1.4Ga0.6O3 samples also exhibited features of exchange bias, low temperature surface paramagnetism, and suppression of Morin transition. These features have been affected up to certain extent by the nano-sized grains of the samples.

cond-mat.mtrl-sci↗

arXiv2012

Room temperature ferromagnetism and giant permittivity in chemical routed Co1.5Fe1.5O4 ferrite particles and their composite with NaNO3

We report structural, magnetic and dielectric properties of Co1.5Fe1.5O4 nanoparticles and their composites with non-magnetic NaNO3. The samples were derived from metal nitrates solution at different pH values. The chemical routed sample was air heated at 200 0C and 500 0C. Heating of the material showed unusual decrease of crystallite size, but cubic spinel structure is seen in all samples. The samples of Co1.5Fe1.5O4 showed substantially large room temperature ferromagnetic moment, electrical conductivity, dielectric constant, and low dielectric loss. The samples are soft ferromagnet and electrically highly polarized. The interfaces of grains and grain boundaries are actively participating to determine the magnetic and dielectric properties of the ferrite grains. The effects of interfacial contribution are better realized using the ferrite and NaNO3 composite samples. We have examined different scopes of modifying the magnetic and dielectric parameters using same material in pure and composite form.

cond-mat.mtrl-sci↗

arXiv2011

Ferromagnetism in lead graphite-pencils and magnetic composite with CoFe2O4 particles

This work has been initiated with a curiosity to investigate the elemental composition and magnetic response of different grades of lead pencils (6B, 2B, HB, 2H, 5H) that people use in daily life. Interestingly, experimental results landed with a great achievement of observing soft magnetism in lead pencils, indicating a wide scope of magnetic tuning for room temperature applications. A novel magnetic composite has been synthesized by mixing different concentration of CoFe2O4 (CF) nanoparticles in 5H and 6B pencils for studying the magnetic tailoring aspects using pencils. Our results showed different possibilities of controlling disorder induced ferromagnetic parameters and a simple approach of producing sufficiently high coercive magnetic composite using pencils.

cond-mat.dis-nn↗

arXiv2011

Synthesis and study of alpha-Fe1.4Ga0.6O3: An advanced Ferromagnetic Semiconductor

We report the synthesis of alpha-Fe1.4Ga0.6O3 compound and present its structural phase stability and interesting magnetic, dielectric and photo-absorption properties. In our work Ga doped alpha-Fe2O3 samples are well stabilized in alpha phase (rhombohedral crystal structure with space group R3C). Properties of the present composition of Ga doped alpha-Fe2O3 system are remarkably advanced in comparison with recently most studied FeGaO3 composition. At room temperature the samples are typical soft ferromagnet, as well as direct band gap semiconductor. Dielectric study showed low dielectric loss in the samples with large enhancement of ac conductivity at higher frequencies. Optical absorption in the visible range has been enhanced by 4 to 5%. This composition has exhibited large scope of tailoring room temperature ferromagnetic moment and optical band gap by varying grain size and non-ambient (vacuum) heat treatment of the as prepared samples by mechanical alloying.

cond-mat.mtrl-sci↗