Papers by Author: Nhalil E. Rajeevan

Abstract: The effect of swift heavy ion (SHI) irradiation on the structural and magnetic properties of thin films of Bi-substituted Co2MnO4 prepared by Pulsed Laser Deposition (PLD) is presented. XRD analysis reveals that the BixCo2-x MnO4 (x = 0.0, 0.1 & 0.3) films grown on amorphous quartz, and crystalline LaAlO3 (LAO) exhibited single phase cubic spinel structure with low strain before and after the irradiation at 200 MeV Ag15+ ions at three fluence values 1 × 1011, 5 × 1011 and 1 × 1012 ions/cm2. DC magnetization hysteresis loop study of the films revealed a ferrimagnetic ordering below the transition temperature ~ 185 K and the saturation magnetization was increased by the irradiation at optimal fluence value 51011 ions/cm2. X-ray Magnetic Circular Dichroism (XMCD) studies showed the antiparallel alignments of Co and Mn magnetic moments.

Abstract: Thermoelectricity has gained special interest due to its potential applications, especially the advancements in the electronic devices with very low power consumption. Thermoelectric materials can be used to make energy conversion devices that generate power from thermal sources. Multiferroic oxides, in particular cobaltates, have been actively studied as a new type of thermoelectric material (1). The crystal structure of these cobaltates offers a possibility to manipulate Seebeck coefficient, electric conductivity, and thermal conductivity to optimize the figure of merit ZT. The theoretical explanation and experimental observations by some investigators proved the candidature of multiferroic materials for thermoelectric generation. Many semiconducting multiferroic oxides are showing spin dependent Seebeck coefficient (2-3). Moreover, most of these oxides are inherently stable at high temperatures in air, making them a suitable material for high temperature applications. In this work we have investigated the multiferroic and thermoelectric properties of thinfilms of doped cobalt oxide matrices. The observations confirmed that these materials are suitable for thermoelectric generation.

Abstract: The attempts to combine both the magnetic and ferroelectric properties in one material started in 1960s predominantly by the group of Smolenskii and Schmid [1. Dzyaloshinskii first presented the theory for multiferroicity in Cr₂O₃, which was soon experimentally confirmed by Astrov [5,. Further work on multiferroics was done by the group of Smolenskii in St. Petersburg (then Leningrad) [7, but the term multiferroic was first used by H. Schmid in 1994 [. These efforts have resulted in many fundamental observations and opened up an entirely new field of study. Schmid [ defined the multiferroics as single phase materials which simultaneously possess two or more primary ferroic properties. The term multiferroic has been expanded to include materials which exhibit any type of long range magnetic ordering, spontaneous electric polarization, and/or ferroelasticity. In the past decade, several hundreds of papers related to multiferroic materials and magnetoelectric effect have been published every year, making this topic one of the hottest areas in condensed matter physics from fundamental science as well as applications viewpoints. This article sheds light on recent progress about the developments of new multiferroics by combining unconventional magnetism and ferroelectricity with an emphasis on Bi based multiferroic materials. Specifically results of Ti doped BiMn₂O₅ and Bi doped Co₂MnO₄ multiferroics are discussed.