The Magnetic Domain Structure Properties in Diluted Magnetic Semiconductors

We present a comprehensive analysis of the domain structure formation in the ferromagnetic phase of diluted magnetic semiconductors (DMS) of the p-type. Our analysis is carried out on the base of the effective magnetic free energy of DMS calculated by us earlier. This free energy, substituting DMS (a disordered magnet) by an effective ordered substance, permits us to apply the standard phenomenological approach to the domain structure calculation. Using the coupled system of Maxwell equations with those obtained by the minimization of the free energy functional, we show the existence of the critical ratio ν_cr of concentration of charge carriers and magnetic ions such that the sample critical thickness L_cr (such that the sample is monodomain at L < L_cr) diverges as v → ν_cr. At ν > ν_cr, the sample is monodomain. This feature makes DMS different from conventional ordered magnets, as it gives a possibility to control the sample critical thickness and the emerging domain structure period by a variation of ν. As the concentration of magnetic impurities grows, ν_cr → ∞, restoring a conventional behavior of ordered magnets. Above facts have been revealed by the examination of the temperature of the transition to an inhomogeneous magnetic state (stripe domain structure) in the slab of a p-type DMS with finite thickness L. Our theory can be easily generalized for an arbitrary disordered magnet. (author)