The Magnetic Domain Structure Properties in Diluted Magnetic Semiconductors

Abstract

We present a comprehensive analysis of the domain structure formation in the ferromagneticphase of diluted magnetic semiconductors (DMS) of the p-type. Our analysis is carried outon the base of the effective magnetic free energy of DMS calculated by us earlier. This freeenergy, substituting DMS (a disordered magnet) by an effective ordered substance, permits usto apply the standard phenomenological approach to the domain structure calculation. Usingthe coupled system of Maxwell equations with those obtained by the minimization of the freeenergy functional, we show the existence of the critical ratio vcr of concentration of chargecarriers and magnetic ions such that the sample critical thickness Lcr (such that the sampleis monodomain at L < Lcr) diverges as v → vcr. At v > vcr, the sample is monodomain. Thisfeature makes DMS different from conventional ordered magnets, as it gives a possibility tocontrol the sample critical thickness and the emerging domain structure period by a variationof v. As the concentration of magnetic impurities grows, vcr → ∞, restoring a conventionalbehavior of ordered magnets. Above facts have been revealed by the examination of the tem-perature of the transition to an inhomogeneous magnetic state (stripe domain structure) inthe slab of a p-type DMS with finite thickness L. Our theory can be easily generalized for anarbitrary disordered magnet.