Magnetic order induced crystal symmetry lowering in ACr$_2$O$_4$ ferrimagnetic spinels

S. Bordacs; D. Varjas; I. Kezsmarki; G. Mihaly; L. Baldassarre; A. Abouelsayed; C. A. Kuntscher; K. Ohgushi; Y. Tokura

doi:10.1103/PhysRevLett.103.077205

paper

Magnetic order induced crystal symmetry lowering in ACr $_{2}$ O $_{4}$ ferrimagnetic spinels

arXiv:0904.3712 · doi:10.1103/PhysRevLett.103.077205

Abstract

We demonstrate that the onset of complex spin orders in ACr $_{2}$ O $_{4}$ spinels with magnetic A $=$ Co, Fe and Cu ions lowers the lattice symmetry. This is clearly indicated by the emergence of anisotropic lattice dynamics -- as evidenced by the pronounced phonon splittings -- even when experiments probing static distortions fail. We show that the crystal symmetry in the magnetic phase is reduced from tetragonal to orthorhombic for FeCr $_{2}$ O $_{4}$ and CuCr $_{2}$ O $_{4}$ with Jahn-Teller active A-site ions. The conical spin structure in FeCr $_{2}$ O $_{4}$ is also manifested in the phonon frequencies. In contrast, the multiferroic CoCr $_{2}$ O $_{4}$ with no orbital degrees of freedom remains nearly cubic in its ground state.

4 pages, 4 figures. submitted to Phys. Rev. Lett

Magnetic order induced crystal symmetry lowering in ACr2​O4​ ferrimagnetic spinels

Abstract

Magnetic order induced crystal symmetry lowering in ACr $_{2}$ O $_{4}$ ferrimagnetic spinels