Author
P. D. Babu
Bio: P. D. Babu is an academic researcher from Bhabha Atomic Research Centre. The author has contributed to research in topics: Magnetization & Ferromagnetism. The author has an hindex of 11, co-authored 74 publications receiving 309 citations.
Papers
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TL;DR: In this article, a correlation between magnetic structure and dielectric properties has been found in the case of Ca3CoMnO6 and the existence of magnetoelectric coupling below magnetic ordering temperature.
Abstract: Magnetic structure and dielectric response of Ca3CoMnO6 have been studied as a function of temperature and applied magnetic field. Neutron diffraction experiments at low temperatures reveal changes in the magnetic structure in the temperature range 2–10 K. The pristine magnetic structure undergoes significant change with the application of magnetic field at these temperatures. Dielectric measurements reveal the presence of magnetoelectric coupling below magnetic ordering temperature (TN=15 K). The present work brings out the existence of a correlation between magnetic structure and dielectric properties.
36 citations
TL;DR: In this paper, the effect of annealing atmosphere on structure and magnetic and dielectric properties of double perovskite-type EuCo0.5Mn 0.5O3 (ECMO) polycrystalline samples prepared by high-temperature reaction were subjected to different oxygen partial pressures and investigated by powder X-ray diffraction, magnetometry, and ac impedance spectroscopy.
Abstract: We report the effect of annealing atmosphere on structure and magnetic and dielectric properties of double perovskite-type EuCo0.5Mn0.5O3 (ECMO). Polycrystalline samples prepared by high-temperature reaction were subjected to annealing in different oxygen partial pressures and investigated by powder X-ray diffraction, magnetometry, and ac impedance spectroscopy. While the samples annealed in air or oxygen environment were found to have cation-disordered orthorhombic structure (Pnma), the samples annealed in inert atmosphere have Eu3+ deficient perovskite-type structure. The temperature- and field-dependent magnetizations indicate the ferromagnetic transition around 130 K. The differences in field-cooled and zero-field-cooled magnetization and significant effect of magnetic field on magnetic properties suggest metamagnetic behavior in ECMO. Randomly distributed clusters of ferromagnetically (FM) and antiferromagnetically (AFM) paired magnetic ions and their relative proportions are reflected in their magne...
30 citations
TL;DR: The existence of two distinct crystalline phases viz., Si2Te3 and SiTe2, in the Si-Te system is established from differential thermal analysis (DTA) studies.
24 citations
TL;DR: In this article, a detailed structural and magnetization analysis of a two-phase ternary Ni55Fe19Ga26 alloy and its quaternary counterparts obtained by partial replacement of Fe by Mn was presented.
20 citations
TL;DR: In this paper, the effects of these two thermal growth processes on the structural and magnetic properties of the films have been studied in detail, where two series of CFS thin films of approximate thickness of 1000 A were prepared using Pulsed Laser Deposition (PLD) technique by two separate routes, viz., (i) by depositing at elevated substrate temperature and (ii) by deposition at room temperature followed by post-deposition annealing under vacuum.
20 citations
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TL;DR: The magnetocaloric effect and its most straightforward application, magnetic refrigeration, are topics of current interest due to the potential improvement of energy efficiency of cooling and temperature control systems, in combination with other environmental benefits associated to a technology that does not rely on the compression/expansion of harmful gases.
941 citations
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TL;DR: The electronic structure of the perovskite LaCoO3 for different spin states of Co ions was calculated in the local-density approximation LDA+U approach and shows that Co 3d states of t(2g) symmetry form narrow bands which could easily localize, while e(g) orbitals, due to their strong hybridization with the oxygen 2p states, form a broad sigma* band.
Abstract: The electronic structure of the perovskite LaCoO$_3$ for different spin states of Co ions was calculated in the LDA+U approach. The ground state was found to be a nonmagnetic insulator with Co ions in a low-spin state. Somewhat higher in energy we found two intermediate-spin states followed by a high-spin state at significantly higher energy. The calculation results show that Co 3$d$ states of $t_{2g}$ symmetry form narrow bands which could easily localize whilst $e_g$ orbitals, due to their strong hybridization with the oxygen 2$p$ states, form a broad $\sigma^*$ band. With the increase of temperature which is simulated by the corresponding increase of the lattice parameter, the transition from the low- to intermediate-spin states occurs. This intermediate-spin (occupation $t_{2g}^5e_g^1$) can develop an orbital ordering which can account for the nonmetallic nature of LaCoO$_3$ at 90 K$<$T$<$500 K. Possible explanations of the magnetic behavior and gradual insulating-metal transition are suggested.
531 citations
01 Apr 2009
TL;DR: In this article, the performance of recent density functionals for the exchange-correlation energy of a nonmolecular solid, by applying accurate calculations with the GAUSSIAN, BAND, and VASP codes to a test set of 24 solid metals and nonmetals.
Abstract: We assess the performance of recent density functionals for the exchange-correlation energy of a nonmolecular solid, by applying accurate calculations with the GAUSSIAN, BAND, and VASP codes to a test set of 24 solid metals and nonmetals. The functionals tested are the modified Perdew-Burke-Ernzerhof generalized gradient approximation PBEsol GGA, the second-order GGA SOGGA, and the Armiento-Mattsson 2005 AM05 GGA. For completeness, we also test more standard functionals: the local density approximation, the original PBE GGA, and the Tao-Perdew-Staroverov-Scuseria meta-GGA. We find that the recent density functionals for solids reach a high accuracy for bulk properties lattice constant and bulk modulus. For the cohesive energy, PBE is better than PBEsol overall, as expected, but PBEsol is actually better for the alkali metals and alkali halides. For fair comparison of calculated and experimental results, we consider the zeropoint phonon and finite-temperature effects ignored by many workers. We show how GAUSSIAN basis sets and inaccurate experimental reference data may affect the rating of the quality of the functionals. The results show that PBEsol and AM05 perform somewhat differently from each other for alkali metal, alkaline-earth metal, and alkali halide crystals where the maximum value of the reduced density gradient is about 2, but perform very similarly for most of the other solids where it is often about 1. Our explanation for this is consistent with the importance of exchange-correlation nonlocality in regions of core-valence overlap.
413 citations
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TL;DR: In this article, the enhancement of ferromagnetism in pure ZnO upon thermal annealing with the ferromagnetic transition temperature Tc above room temperature has been reported.
Abstract: We report here enhancement of ferromagnetism in pure ZnO upon thermal annealing with the ferromagnetic transition temperature Tc above room temperature. We observe a finite coercive field upto 300K and a finite thermoremanent magnetization upto 340K for the annealed sample. We propose that magnetic moments can form at anionic vacancy clusters. Ferromagnetism can occur due to either superexchange between vacancy clusters via isolated F+ centers, or through a limited electron delocalization between vacancy clusters. Isolated vacancy clusters or isolated F+ centers give rise to a strong paramagnetic like behaviour below 10K.
274 citations