Vasudeva Siruguri

Bio: Vasudeva Siruguri is an academic researcher from Bhabha Atomic Research Centre. The author has contributed to research in topics: Neutron diffraction & Magnetization. The author has an hindex of 21, co-authored 150 publications receiving 1781 citations. Previous affiliations of Vasudeva Siruguri include University of the Basque Country.

Substantial magnetoelectric coupling near room temperature in Bi2Fe4O9

Abstract: We report remarkable multiferroic effects in polycrystalline Bi2Fe4O9. High-resolution x-ray diffraction shows that this compound has orthorhombic structure. Magnetic measurements confirm an antiferromagnetic transition around 260K. A pronounced inverse S-shape anomaly in the loss tangent of dielectric measurement is observed near the Neel temperature. This feature shifts with the application of magnetic field. These anomalies are indicative of substantial coupling between the electric and magnetic orders in this compound.

Neutron diffraction studies of perovskite-type compounds

Abstract: Neutron diffraction measurements on the title compounds have been carried out over a range of temperature from 10 to 300 K. The compounds have a rhombohedrally distorted perovskite structure. A paramagnetic to ferromagnetic transition is observed for samples with . The ordered magnetic moments obtained for x = 0.2 and 0.3 are found to be 1.5 and respectively at 10 K and are in agreement with those reported from other macroscopic measurements. A possible magnetic structure is discussed.

Magnetism driven ferroelectricity above liquid nitrogen temperature in Y2CoMnO6

Abstract: We report multiferroic behaviour in double perovskite Y2CoMnO6 with ferroelectric transition temperature Tc = 80 K. Both X-ray diffraction and neutron scattering data confirm a centro-symmetric crystal structure of space group P21/n at room temperature. The saturation polarization and magnetization are estimated to be 65 μC/m2 and 6.2 μB/f.u. respectively. The magneto-electric coupling parameter, on the other hand, is small as a 5 T field suppresses the electric polarization by only ∼8%. The origin of ferroelectricity is associated with magnetic ordering of Co2+ and Mn4+ moments in ↑↑-↓↓ arrangement. A model based on exchange-striction is proposed to explain the observed high temperature ferroelectricity.

A high resolution powder diffractometer using focusing optics

Abstract: In this paper, we describe the design, construction and performance of a new high resolution neutron powder diffractometer that has been installed at the Dhruva reactor, Trombay, India. The instrument employs novel design concepts like the use of bent, perfect crystal monochromator and open beam geometry, enabling the use of smaller samples. The resolution curve of the instrument was found to have little variation over a wide angular region and a Δd/d ∼ 0.3% has been achieved. The instrument provides sample environment of very low temperatures and high magnetic fields using a 7 Tesla cryogen-free superconducting magnet with a VTI having a temperature range of 1.5–320 K. The special sample environment and high resolution make this neutron powder diffractometer a very powerful facility for studying magnetic properties of materials.

Origin of the Spin-Orbital Liquid State in a Nearly J=0 Iridate Ba3ZnIr2O9

Abstract: We show using detailed magnetic and thermodynamic studies and theoretical calculations that the ground state of Ba3ZnIr2O9 is a realization of a novel spin-orbital liquid state. Our results reveal that Ba3ZnIr2O9 with Ir5+ (5d(4)) ions and strong spin-orbit coupling (SOC) arrives very close to the elusive J = 0 state but each Ir ion still possesses a weak moment. Ab initio density functional calculations indicate that this moment is developed due to superexchange, mediated by a strong intradimer hopping mechanism. While the Ir spins within the structural Ir2O9 dimer are expected to form a spin-orbit singlet state (SOS) with no resultant moment, substantial frustration arising from interdimer exchange interactions induce quantum fluctuations in these possible SOS states favoring a spin-orbital liquid phase down to at least 100 mK.

Ferromagnetic materials

Abstract: In this chapter, we will restrict our attention to the ferrites and a few other closely related materials. The great interest in ferrites stems from their unique combination of a spontaneous magnetization and a high electrical resistivity. The observed magnetization results from the difference in the magnetizations of two non-equivalent sub-lattices of the magnetic ions in the crystal structure. Materials of this type should strictly be designated as “ferrimagnetic” and in some respects are more closely related to anti-ferromagnetic substances than they are to ferromagnetics in which the magnetization results from the parallel alignment of all the magnetic moments present. We shall not adhere to this special nomenclature except to emphasize effects, which are due to the existence of the sub-lattices.

Models and materials for generalized Kitaev magnetism.

Abstract: The exactly solvable Kitaev model on the honeycomb lattice has recently received enormous attention linked to the hope of achieving novel spin-liquid states with fractionalized Majorana-like excitations. In this review, we analyze the mechanism proposed by Jackeli and Khaliullin to identify Kitaev materials based on spin-orbital dependent bond interactions and provide a comprehensive overview of its implications in real materials. We set the focus on experimental results and current theoretical understanding of planar honeycomb systems (Na2IrO3, α-Li2IrO3, and α-RuCl3), three-dimensional Kitaev materials (β- and γ-Li2IrO3), and other potential candidates, completing the review with the list of open questions awaiting new insights.

First-principles calculations of electronic structure and spectra of strongly correlated systems: the LDA+U method

Abstract: The generalization of the Local Density Approximation (LDA) method for the systems with strong Coulomb correlations is presented which gives a correct description of the Mott insulators. The LDA+U method is based on the model hamiltonian approach and allows to take into account the non-sphericity of the Coulomb and exchange interactions. parameters. Orbital-dependent LDA+U potential gives correct orbital polarization and corresponding Jahn-Teller distortion. To calculate the spectra of the strongly correlated systems the impurity Anderson model should be solved with a many-electron trial wave function. All parameters of the many-electron hamiltonian are taken from LDA+U calculations. The method was applied to NiO and has shown good agreement with experimental photoemission spectra and with the oxygen Kα X-ray emission spectrum.