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We present a unified interpretation of experimentally observed magnetic circular dichroism (MCD) in the ferromagnetic semiconductor (Ga,Mn)As, based on theoretical arguments, which demonstrates that MCD in this material arises primarily from a difference in the density of spin-up and spin-down states in the valence band brought about by the presence of the Mn impurity band, rather than being primarily due to the Zeeman splitting of electronic states.

We present a detailed investigation of exchange-dominated nonpropagating spin-wave modes in a series of 100 nm Ga1−xMnxAs films with Mn concentrations x ranging from 0.02 to 0.08. The angular and Mn concentration dependences of spin wave resonance modes have been studied for both as-grown and annealed samples. Our results indicate that the magnetic anisotropy terms of Ga1−xMnxAs depend on the Mn concentration x, but are also strongly affected by sample growth conditions; moreover, the magnetic anisotropy of Ga1−xMnxAs films is found to be clearly linked to the Curie temperature. The spin wave resonance spectra consist of a series of well resolved standing spin-wave modes. The observed mode patterns are consistent with the Portis volume-inhomogeneity model, in which a spatially nonuniform anisotropy field acts on the Mn spins. The analysis of these exchange-dominated spin wave modes, including their angular dependences, allows us to establish the exchange stiffness constants for Ga1−xMnxAs films.

A systematic investigation of ferromagnetic resonance ͑FMR͒ was carried out on Ga 1−x Mn x As layers synthesized by Mn ion implantation into GaAs followed by pulsed laser melting. Angular and temperature dependences of FMR were measured on layers prepared on GaAs ͑001͒, ͑110͒, and ͑311͒ surfaces. The observed angular dependence of FMR can be understood in terms of contributions from cubic anisotropy fields defined by the crystal symmetry of Ga 1−x Mn x As and uniaxial anisotropy fields perpendicular or parallel to the film plane. For completeness, the angular dependence of the FMR linewidth was also investigated and was found to be dominated by broadening ascribed to local inhomogeneities in magnetic anisotropy. Our results show that both the magnetic anisotropy and the FMR linewidth in ͑Ga,Mn͒As prepared by ion implantation are similar to those observed on Ga 1−x Mn x As samples grown by low-temperature molecular beam epitaxy, indicating that the two very different growth methods lead to materials with fundamentally similar magnetic properties.

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