Ultrasound velocity measurements of the magnesium chromite spinel MgCr 2O 4 reveal elastic anomalies in the paramagnetic phase that are characterized as due to geometrical frustration. The temperature dependence of the tetragonal shear modulus (C 11-C 12)/2 exhibits huge Curie-type softening, which should be the precursor to spin Jahn-Teller distortion in the antiferromagnetic phase. The trigonal shear modulus C 44 exhibits nonmonotonic temperature dependence with a characteristic minimum at ∼50 K, indicating a coupling of the lattice to a dynamical molecular-spin state. These results strongly suggest the coexistence of the dynamical spin Jahn-Teller effect and a dynamical molecular-spin state in the paramagnetic phase, which is compatible with the coexistence of magnetostructural order and a dynamical molecular-spin state in the antiferromagnetic phase.
|Journal||Physical Review B - Condensed Matter and Materials Physics|
|Publication status||Published - 2012 Oct 22|
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics