Magnetic and magnetocaloric properties of HoCr0.75Fe0.25O3 compound

We report on the magnetic and magnetocaloric properties of HoCr0.75Fe0.25O3 compound around the Néel temperature (TN), which is due to Cr3+ ordering. Susceptability (χ) vs. temperature (T) graph of HoCr0.75Fe0.25O3 compound infer two transitions due to the ordering of Cr3+ moments (TN ~ 155 K) and Ho3+ moments (TNHo ~ 8 K). Magnetic entropy (–ΔSM) value of 1.14 J kg-1 K-1 around 157.5 K with a magnetic field (H) of 90 kOe is attributed to antiferromagnetic (AFM) ordering of Cr3+ moments. A maximum value of adiabatic temperature (ΔTad) ~ 0.41 K around TN is obtained and is found to increases with applied magnetic field. Negative slope for H/M vs. M2 graph is evident for HoCr0.75Fe0.25O3 compound below TN, which indicates the first order phase transition. Quantified values of – ΔSM and ΔTad opens up the way to explore rare earth orthochromites for the MCE properties and refrigeration applications

Magnetic properties and their correlation with lattice dynamics in HoFe1-xCrxO3 (0 ≤ x ≤ 1) compounds

Perovskites with general formula ABO3 (A is rare earth ion or Yttrium and B is a transition metal) have been the most versatile compounds in oxide research. Among various perovskite oxides, rare earth orthoferrite (RFeO3) and orthochromite (RCrO3) compounds with distorted perovskite structure have drawn considerable attention due to their unique physical properties and potential applications. Among RFeO3 compounds, holmium orthoferrite (HoFeO3) has been studied extensively for ultrafast recording applications. The crystal structure of HoFeO3 is orthorhombic with a space group of Pbnm at room temperature and possesses G-type antiferromagnetic with a magnetic ordering temperature (TN) around 641 K. Apart from TN, HoFeO3 exhibits the spin reorientation (SR) transition of Fe3+ at 50 - 60 K. According to Goodenough-Kanamori theory, Cr3+ is best choice for Fe3+ to show superior magnetic properties due to super exchange interactions, which may exhibit interesting magnetic properties and lattice dynamics. Hence, in this thesis we explored the structural, magnetic properties and their correlation with lattice dynamics in HoFe1- xCr xO 3 (0 ≤ x ≤ 1) compounds

Band gap tuning and orbital mediated electron–phonon coupling in HoFe1−xCrxO3 (0 ≤ x ≤ 1)

We report on the evidenced orbital mediated electron–phonon coupling and band gap tuning in HoFe1−xCrxO3 (0 ≤ x ≤ 1) compounds. From the room temperature Raman scattering, it is apparent that the electron-phonon coupling is sensitive to the presence of both the Fe and Cr at the B-site. Essentially, an Ag like local oxygen breathing mode is activated due to the charge transfer between Fe3+ and Cr3+ at around 670 cm−1, this observation is explained on the basis of Franck-Condon mechanism. Optical absorption studies infer that there exists a direct band gap in the HoFe1−xCrxO3 (0 ≤ x ≤ 1) compounds. Decrease in band gap until x = 0.5 is ascribed to the broadening of the oxygen p-orbitals as a result of the induced spin disorder due to Fe3+ and Cr3+ at B-site. In contrast, the increase in band gap above x = 0.5 is explained on the basis of the reduction in the available unoccupied d-orbitals of Fe3+ at the conduction band. We believe that above results would be helpful for the development of the optoelectronic devices based on the ortho-ferrites

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

Abstract Low-cost and scalable sol–gel 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

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

Metamagnetic Transitions and Magnetocaloric Properties of HoCr1-xFexO3 (x = 0.25 and 0.75) Compounds

We report on the magnetocaloric properties of HoCr1-xFexO3 (x = 0.25 and 0.75) compounds studied by magnetic and specific heat measurements. The magnetic entropy change (–ΔSM) reaches a maximum value of 10.32 J/kg-K and 10.94 J/kg-K around 11 K with a maximum magnetic field of 9 T in HoCr0.75Fe0.25O3 and HoCr0.25Fe0.75O3 compounds respectively. The corresponding adiabatic temperature change (ΔTad) values are found to be 13.7 K and 18.5 K with a maximum magnetic field of 7 T from the specific heat studies. The origin for the obtained large values of –ΔSM and ΔTad are attributed to the evidenced metamagnetic transition and Ho3+ ordering. The evidenced Schottky anomaly below 15 K in the specific heat data is ascribed to crystal field splitting of 5I8 levels of Ho3+ paramagnetic ions. The Debye temperatures and splitting energy of Ho3+ ground state levels have been evaluated by fitting the specific heat data. The present results suggest that HoCr1-xFexO3 (x = 0.25 and 0.75) compounds could be promising candidates for the refrigeration applications below 30 K. © 2022, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature