Magnetic-order-induced crystal symmetry lowering in ACr2O4 ferrimagnetic spinels.

  title={Magnetic-order-induced crystal symmetry lowering in ACr2O4 ferrimagnetic spinels.},
  author={S{\'a}ndor Bord{\'a}cs and D{\'a}niel Varjas and Istv{\'a}n K{\'e}zsm{\'a}rki and Gy{\"o}rgy Mih{\'a}ly and Leonetta Baldassarre and A. Abouelsayed and C. A. Kuntscher and Kenya Ohgushi and Yasuhiro Tokura},
  journal={Physical review letters},
  volume={103 7},
We demonstrate that the onset of complex spin orders in ACr2O4 spinels with magnetic and Jahn-Teller active A=Fe and Cu ions lowers the lattice symmetry. This is clearly indicated by the emergence of anisotropic lattice dynamics-i.e., by the pronounced phonon splittings-even when experiments probing static distortions fail. The crystal symmetry in the magnetic phase is reduced from tetragonal to orthorhombic for both compounds. The conical spin ordering in FeCr2O4 is also manifested in the… 

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However, a cubic to orthorhombic structural change at T C seems to be incompatible with the second-order nature of the magnetic transition