Abstract
We derive an effective Hamiltonian for in the dilute limit, where can be described in terms of spin holes hopping between the Mn sites and coupled to the local Mn spins. We determine the parameters of our model from microscopic calculations using both a variational method and an exact diagonalization within the so-called spherical approximation. Our approach treats the extremely large Coulomb interaction in a nonperturbative way and captures the effects of strong spin-orbit coupling and Mn positional disorder. We study the effective Hamiltonian in a mean-field and variational calculation, including the effects of interactions between the holes at both zero and finite temperature. We study the resulting magnetic properties, such as the magnetization and spin-disorder manifest in the generically noncollinear magnetic state. We find a well-formed impurity band fairly well separated from the valence band up to for which finite-size scaling studies of the participation ratios indicate a localization transition, even in the presence of strong on-site interactions, where is the fraction of magnetically active Mn. We study the localization transition as a function of hole concentration, Mn positional disorder, and interaction strength between the holes.
6 More- Received 29 March 2005
DOI:https://doi.org/10.1103/PhysRevB.72.045212
©2005 American Physical Society