Spin orbital reorientation transitions induced by magnetic field

Abstract

Here we report on a new effect similar to the spin reorientation transition (SRT) that takes place at two magnetic fields of BSORT 1 and BSORT 2. The effect is observed in the magnetization curves of small Mn 3+ magnetic clusters in the wurtzite GaN (being in a paramagnetic state) calculated using crystal field model approach. The obtained results suggest that the computed magnetic anisotropy (MA) reverses its sign on increasing B across BSORT . Detailed analysis show however that MA is unchanged for high magnetic fields. We show that the observed effect arises from the interplay of the crystalline environment and the spin-orbit coupling λ ŜL , therefore we name it spin orbital reorientation transition (SORT). The value of BSORT 1 depends on the crystal field model parameters and the number of ions N in a given cluster, whereas BSORT 2 is controlled mostly by the magnitude of the spin-orbit coupling λ. The explanation of SORT is given in terms of the spin MS and orbital momentum ML contributions to the total magnetization M = MS + ML. The similar effect should also be present in other materials with not completely quenched (non zero) orbital angular momentum L, an uniaxial magnetic anisotropy and the positive value of λ.