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arXiv · 1302.5746

Crystal structures of spin-Jahn-Teller ordered MgCr_2O_4 and ZnCr_2O_4

Moureen C. Kemei·Phillip T. Barton·Stephanie L. Moffitt·Michael W. Gaultois·Joshua A. Kurzman·Ram Seshadri·Matthew R. Suchomel·Young-II Kim
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Abstract

Magnetic ordering in the geometrically frustrated magnetic oxide spinels MgCr_2O_4 and ZnCr_2O_4 is accompanied by a structural change that helps relieve the frustration. Analysis of high-resolution synchrotron X-ray scattering reveals that the low-temperature structures are well described by a two-phase model of tetragonal I4_1/amd and orthorhombic Fddd symmetries. The Cr_4 tetrahedra of the pyrochlore lattice are distorted at these low-temperatures, with the Fddd phase displaying larger distortions than the I4_1/amd phase. The spin-Jahn-Teller distortion is approximately one order of magnitude smaller than is observed in first-order Jahn-Teller spinels such as NiCr_2O_4 and CuCr_2O_4. In analogy with NiCr_2O_4 and CuCr_2O_4, we further suggest that the precise nature of magnetic ordering can itself provide a second driving force for structural change.

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Moureen C. Kemei, Phillip T. Barton, Stephanie L. Moffitt, Michael W. Gaultois, Joshua A. Kurzman, Ram Seshadri, Matthew R. Suchomel, Young-II Kim. 2013-03-05. Crystal structures of spin-Jahn-Teller ordered MgCr_2O_4 and ZnCr_2O_4. https://doi.org/10.1088/0953-8984%2F25%2F32%2F326001

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