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Phase Equilibria in the System $Al_{2}O_{3}-CaO-CoO$ and Gibbs Energy of Formation of $Ca_{3}CoAl_{4}O_{10}$

Jacob, KT and Shekhar, Chander and Kale, GM (2009) Phase Equilibria in the System $Al_{2}O_{3}-CaO-CoO$ and Gibbs Energy of Formation of $Ca_{3}CoAl_{4}O_{10}$. In: Journal of Phase Equilibria and Diffusion, 30 (1). pp. 2-11.

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Abstract

The floating-zone method with different growth ambiences has been used to selectively obtain hexagonal or orthorhombic DyMnO3 single crystals. The crystals were characterized by x-ray powder diffraction of ground specimens and a structure refinement as well as electron diffraction. We report magnetic susceptibility, magnetization and specific heat studies of this multiferroic compound in both the hexagonal and the orthorhombic structure. The hexagonal DyMnO3 shows magnetic ordering of Mn3+ (S = 2) spins on a triangular Mn lattice at T-N(Mn) = 57 K characterized by a cusp in the specific heat. This transition is not apparent in the magnetic susceptibility due to the frustration on the Mn triangular lattice and the dominating paramagnetic susceptibility of the Dy3+ (S = 9/2) spins. At T-N(Dy) = 3 K, a partial antiferromagnetic order of Dy moments has been observed. In comparison, the magnetic data for orthorhombic DyMnO3 display three transitions. The data broadly agree with results from earlier neutron diffraction experiments, which allows for the following assignment: a transition from an incommensurate antiferromagnetic ordering of Mn3+ spins at T-N(Mn) = 39 K, a lock-in transition at Tlock-in = 16 K and a second antiferromagnetic transition at T-N(Dy) = 5 K due to the ordering of Dy moments. Both the hexagonal and the orthorhombic crystals show magnetic anisotropy and complex magnetic properties due to 4f-4f and 4f-3d couplings.

Item Type: Journal Article
Additional Information: Copyright of this article belongs to ASM International.
Keywords: chemical potential;electromotive force (emf);enthalpy of formation;entropy;experimental thermodynamics;Gibbs energy; ternary phase diagram
Department/Centre: Division of Mechanical Sciences > Materials Engineering (formerly Metallurgy)
Depositing User: Rajalaxmi Ashok Govanakoppa
Date Deposited: 06 Nov 2009 08:34
Last Modified: 19 Sep 2010 05:28
URI: http://eprints.iisc.ac.in/id/eprint/19477

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