Enhanced spin – reorientation temperature and origin of magnetocapacitance in HoFeO3

We report on the increase in the spin reorientation temperature in HoFe0.5Cr0.5O3 compound by isovalent substitution (Cr3+) at the Fe-site and the magnetocapacitance in the HoFeO3 compound. Spin reorientation transition is evident around 50 K and 150 K for the x=0 and x=0.5 compounds respectively. The increase in the spin reorientation transition temperature in case of x=0.5 compound can be attributed to the domination of the Ho3+- Fe3+ interaction over the Fe3+- Fe3+ interaction. Decrease in Néel temperature from 643 K (x=0) to 273 K (x=0.5) can be ascribed to the decrease in the interaction between antiferromagnetically aligned Fe3+ moments as a result of the dilution of the Fe3+ moments with the Cr3+ addition. From the magnetization M vs. magnetic field H variation it is evident that the coercivity, HC decreases for x=0.5 compound, hinting the magnetic softening of the HoFeO3 compound. Observed magnetocapacitance could be due to lossy dielectric mechanism in the present compound. Indeed, present results would be helpful in understanding the physics behind rare- earth orthoferrites

Magnetocaloric effect and nature of magnetic transition in low dimensional DyCu2

In this manuscript, we propose a method to prepare small flakes of DyCu2. On top of that we also report on the magnetocaloric effect and nature of magnetic transition of a strongly anisotropic DyCu2 in its low dimension. Magnetization measurements were carried out in the temperature range of 5-100 K and up to the maximum magnetic field strength of 50 kOe. Magnetic entropy change (Delta S-M) is estimated using the well-known Maxwell's equations and is found to be -4.31 J/kg-K. Indeed, the Delta S-M peak broadened marginally compared with its bulk DyCu2 and such a broadening can be attributed to significant increase in the total grain boundary volume. As these small flakes consists larger DSM values at temperatures higher than the Neel temperature (T-N), one can use them as a magnetic refrigerant material in a broad temperature range. We also plotted the M-2 vs. H/M (which are called as the Arrott plots) in order to find the nature of magnetic transition. Arrott plots infer that indeed there exists nonlinearity in M-2 vs. H/M behavior and such nonlinear behavior is ascribed to the random anisotropy or a random field that is present in the system

Novel mixed precursor approach to prepare multiferroic nanocomposites with enhanced interfacial coupling

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Magnetic and hyperfine interactions in HoFe1−xCrxO3 (0≤x≤1) compounds

We report on the magnetic and Mössbauer properties of polycrystalline HoFe1-xCrxO3 (0≤x≤1) compounds. Magnetization data reveals the continuous tailoring of magnetic transition due to weakening of Ho3+-Fe3+ and Fe3+-Fe3+ interactions in the entire temperature range by replacing the Fe3+ ions with Cr3+ ions. The observed decrease in Néel temperature (TN) and increase in spin re-orientation transition temperature (TSR) with the replacement of Fe3+ with Cr3+ is ascribed to the weakening of Fe(Cr)-O-Fe(Cr) antiferromagnetic exchange interaction. In addition, we also attribute such a change in TN to the enhancement of ferromagnetic interaction of adjacent Cr3+ moments through t-e hybridization as a result of the structural distortion. The decrease in isomer shift (IS) suggests enhancement of the interaction between nuclear charge with the 3s electrons as a result of decrease in radial part of 3d wave function with Cr addition. In this paper we also discuss about the variation of quadrupole splitting (QS) and hyperfine fields (Hhf) with Cr addition in HoFe1-xCrxO3 (0≤x≤1) compounds

Inverse and enhanced magnetocaloric properties of HoCrO3

We report on the magnetic and magnetocaloric properties of 50% Fe3+ doped polycrystalline HoCrO3 compounds in the vicinity of magnetic transitions. Due to complex magnetic interactions, we do see multiple transitions in χ vs. T graph pertinent to HoCrO3 and HoCr0.5Fe0.5O3 compounds related with Ho3+ ordering, Cr3+ ordering and spin – reorientation (SR). Due to re-orientation of spins, metamagnetic transitions are evident in low field regime of M vs. H. Quantified values of -ΔSM around Ho3+ ordering infer that indeed Fe3+ substitution helped in enhancing magnetocaloric effect of HoCrO3 compound. Such an enhanced -ΔSM values are ascribed to increase in canting of Fe/Cr spins. Present results would be helpful in developing magnetic refrigerant materials for space applications particularly below 30 K

Magnetocaloric properties of HoFe0.5Cr0.5O3 compound

We report on the magnetic and magnetocaloric properties of HoFe0.5Cr0.5O3 compound. The nature of the magnetic phase transitions is explained with the help of Arrott's plots. Evidenced metamgnetic transitions are attributed to the reorientation of the moments which are aligned antiparallel to the applied magnetic field. Magnetocaloric properties are analyzed from the isothermal magnetization measurements. The large value of magnetic entropy of 8.18 J/kg.K at 12.5 K with 6 T observed for HoFe0.5Cr0.5O3 compound is due to the ordering of Ho3+ moments

Structural and spectroscopic studies on HoCr1-xFexO3 (x = 0 and 0.5) compounds

We report on the structural and spectroscopic studies on HoCr1-xFexO3 (x = 0 and 0.5) compounds. X-ray diffraction studies confirmed the phase purity of the compounds. An increase in the lattice parameter as well as bond lengh are evident with the addition of Fe at Cr-site in HoCrO3 compound. The addition of Fe content to Cr-site in HoCrO3 compound led to shift the position of phonon mode in Raman spectra as well as position of vibrational bands in FTIR specta recorded at room temperature. Temperature dependent Raman studies on both the compounds indicate the absence of structural phase transition in the investigated temperature region

Structural and spectroscopic studies on HoCr1-xFexO3 (x = 0 and 0.5) compounds

We report on the structural and spectroscopic studies on HoCr1-xFexO3 (x = 0 and 0.5) compounds. X-ray diffraction studies confirmed the phase purity of the compounds. An increase in the lattice parameter as well as bond lengh are evident with the addition of Fe at Cr-site in HoCrO3 compound. The addition of Fe content to Cr-site in HoCrO3 compound led to shift the position of phonon mode in Raman spectra as well as position of vibrational bands in FTIR specta recorded at room temperature. Temperature dependent Raman studies on both the compounds indicate the absence of structural phase transition in the investigated temperature region

Synthesis of BaTiO3-CoFe2O4 nanocomposites using a one-pot technique

Low-cost and scalable sol\u2013gel chemistry was employed to obtain ferroelectric-ferrimagnetic BaTiO3-CoFe2O4 nanocomposites. In a novel one-pot synthesis method, both the constituent phases of nanocomposites are formed during the same time and symbiotically participate to each other's growth. X-ray powder diffraction evidences the phase purity of the systems, with average crystallite sizes in the order of 20 nm for the BaTiO3 phase. The optimization of the synthesis conditions, precursors, and chemical agents for nanoscale BaTiO3 and BaTiO3-CoFe2O4 nanocomposites is presented, together with the magnetic and/or dielectric properties of the obtained materials. BaTiO3-CoFe2O4 nanocomposites with up to 20% CoFe2O4 volume fractions were found to display ferrimagnetic properties at room temperature akin to those of CoFe2O4, while preserving a dielectric behavior reminiscent of BaTiO3. Preliminary results describing the spin coating of BaTiO3 and BaTiO3-CoFe2O4 nanocomposites as thin films are also reported

Novel mixed precursor approach to prepare multiferroic nanocomposites with enhanced interfacial coupling

none7In the present work, we report the preparation of multiferroic PbZr0.52Ti0.48O3 (PZT)/CoFe2O4 (CFO) nanocomposites using a new synthesis technique that can maximize the surface area of contact, and hence, the interfacial coupling between the ferroelectric (PZT) and ferrimagnetic (CFO) phases. The samples have been characterized using X-ray diffraction (XRD) and transmission electron microscopy (TEM), and the physical (magnetic and dielectric) properties have been investigated. XRD confirms the presence of the desired PZT and CFO phases in the samples without any undesired secondary phases. We also observe a reduction in the particle size of CFO in the nanocomposites as evidenced by a line broadening of the XRD reflections corresponding to the pure CFO phase. The nanocomposites show hysteresis loops and ferrimagnetic-like behaviors in their M vs H curves at room temperature, even for samples with very low fraction of the CFO phase. The coercivity of the nanocomposites is marginally larger compared to that of pure CFO, which can be due to the change in magnetic anisotropy of the CFO phase due to its reduced particle size in the nanocomposites. Room temperature polarization versus electric field measurements show a significant increase in the coercive field after the incorporation of CFO inside the PZT matrix. This work illustrates a simple, cost-effective synthesis technique that can be used to prepare nanocomposites of functional materials with desired room temperature functionalities and enhanced interfacial coupling between the two phases.openKotnana G.; Sayed F.; Joshi D.C.; Barucca G.; Peddis D.; Mathieu R.; Sarkar T.Kotnana, G.; Sayed, F.; Joshi, D. C.; Barucca, G.; Peddis, D.; Mathieu, R.; Sarkar, T