Lattice Deformations Induced by an Applied Magnetic Field in the Frustrated Antiferromagnet HgCr_2O_4(Condensed matter: electronic structure and electrical, magnetic, and optical properties)

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The way geometric frustration in the pyrochlore antiferromagnet HgCr_2O_4 is relieved by an applied magnetic field is studied by synchrotron X-ray diffraction. The material shows a structural change, from cubic to orthorhombic, at the magnetic transition temperature, T_N[〜!-]6K, to relieve the geometrical frustration. Below T_N, successive magnetic phase transitions occur in an applied field, from the antiferromagnetic to the half-magnetization plateau phase followed by a transition with a kink in the magnetization. We find that the lattice constant shows discontinuous expansions that coincide with magnetization changes, indicating progressive relief of geometric frustration. We calculate the lattice deformation invoking a magneto-elastic coupling and obtain good agreement between the calculation and our observation.
社団法人日本物理学会の論文
2007-04-15