Disorder-induced noncollinear ferromagnetism in models for „III,Mn...V semiconductors
نویسنده
چکیده
We study the ground-state properties of kinetic-exchange models for ~III,Mn!V semiconductors with randomly distributed Mn ions. Our method is embedded in a path integral spin-wave-type formalism leading to an effective action for Mn spins only with full Matsubara frequency dependence. The zero-frequency contribution to this action is equivalent to static perturbation theory and characterizes the stability of a given spin configuration, while the component linear in frequency can be interpreted as the joint Berry phase of the Mn and carrier system. For simple parabolic-band carriers the collinear ferromagnetic state with all Mn spins in parallel is always stationary but generically unstable. This instability can be characterized in terms of inverse participation ratios and is due to long-ranged nonlocal spin fluctuations. We also present results for the ground-state magnetization as a function of an external field. For carrier dispersions involving anisotropy induced by spin-orbit coupling the collinear state is not even stationary and therefore also not the ground state. This interplay between the anisotropy in the carrier system and the disorder in the Mn positions reflects recent findings by Zarand and Janko @Phys. Rev. Lett. 89, 047201 ~2002!# obtained within the RKKY approximation. The stationarity of the collinear state ~with the magnetization pointing in one of the cubic symmetry directions! is restored in the continuum or virtual crystal approximation where disorder is neglected.
منابع مشابه
Ferromagnetism in magnetically doped III-V semiconductors.
The origin of ferromagnetism in semimagnetic III-V materials is discussed. The indirect exchange interaction caused by virtual electron excitations from magnetic impurity acceptor levels to the valence band can explain ferromagnetism in GaAs(Mn) in both degenerate and nondegenerate samples. Formation of ferromagnetic clusters and the percolation picture of phase transition describes well all av...
متن کاملFerromagnetism of magnetic semiconductors—Zhang-Rice limit
It is suggested that p-d hybridization contributes significantly to the hole binding energy Eb of Mn acceptors in III-V compounds, leading in an extreme case to the formation of Zhang-Rice-like small magnetic polarons. The model explains both strong increase of Eb and evolution of Mn spinresonance spectrum with the magnitude of valence-band offsets. For such a structure of Mn impurity in III-V ...
متن کاملDielectric function of diluted magnetic semiconductors in the infrared regime
We present a study of the dielectric function of metallic (III,Mn)V diluted magnetic semiconductors in the infrared regime. Our theoretical approach is based on the kinetic exchange model for carrier induced (III,Mn)V ferromagnetism. The dielectric function is calculated within the random phase approximation and, within this metallic regime, we treat disorder effects perturbatively and thermal ...
متن کاملTheory of Ferromagnetism in Diluted Magnetic Semiconductors
Carrier-induced ferromagnetism has been observed in several (III,Mn)V semiconductors. We review the theoretical picture of these ferromagnetic semiconductors that emerges from a model with kinetic-exchange coupling between localized Mn spins and valence-band carriers. We discuss the applicability of this model, the validity of a mean-field approximation for its interaction term widely used in t...
متن کامل