Diluted orbital degeneracy and large orthorhombic distortions in ferrimagnetic spinel CuxMn3-xO4

Abstract

We report large orthorhombic distortions in the ferrimagnetic tetragonal (c > a) spinel CuxMn3-xO4 stabilized by a few percent of Cu doping. The orthorhombic strains of the ferrimagnetic phases increased linearly to the doping and reached up to is an element of approximate to 8.2 x 10(-3) for x = 0.19, which is three times larger than the saturated value under external magnetic fields. For high doping (x greater than or similar to 0.17), the distortions first appeared in the paramagnetic phases and underwent further enhancement simultaneously with the onset of the noncollinear ferrimagnetic ordering. We present the rich magnetostructural phase diagram of CuxMn3-xO4, and argue that the diluted t(2) orbital degeneracy of Cu2+ under tetrahedral crystal field breaks the global symmetry and triggers the orthorhombic instability inherent in Mn3O4.