title: Crystal structures of spin-Jahn-Teller-ordered MgCr2O4 and ZnCr2O4.
abstract: Magnetic ordering in the geometrically frustrated magnetic oxide spinels MgCr2O4 and ZnCr2O4 is accompanied by a structural change that helps to 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 I41/amd and orthorhombic Fddd symmetries. The Cr4 tetrahedra of the pyrochlore lattice are distorted at these low-temperatures, with the Fddd phase displaying larger distortions than the I41/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 NiCr2O4 and CuCr2O4. In analogy with NiCr2O4 and CuCr2O4, we further suggest that the precise nature of magnetic ordering can itself provide a second driving force for structural change.
authors.affiliation: Materials Department and Materials Research Laboratory, University of California, Santa Barbara, CA 93106, USA. kemei@mrl.ucsb.edu
authors.forename: Moureen C
authors.initials: MC
authors.lastname: Kemei
authors.forename: Phillip T
authors.initials: PT
authors.lastname: Barton
authors.forename: Stephanie L
authors.initials: SL
authors.lastname: Moffitt
authors.forename: Michael W
authors.initials: MW
authors.lastname: Gaultois
authors.forename: Joshua A
authors.initials: JA
authors.lastname: Kurzman
authors.forename: Ram
authors.initials: R
authors.lastname: Seshadri
authors.forename: Matthew R
authors.initials: MR
authors.lastname: Suchomel
authors.forename: Young-Il
authors.initials: YI
authors.lastname: Kim