Ferromagnetic resonance study of free hole contribution to magnetization and magnetic anisotropy in modulation-doped Ga${}_{1-x}$Mn${}_x$As/Ga${}_{1-y}$Al${}_y$As:Be

Abstract

Ferromagnetic resonance (FMR) is used to study magnetic anisotropy of GaMnAs in a series of Ga${}_{1-x}$Mn${}_x$As/Ga${}_{1-y}$Al${}_y$As heterostructures modulation-doped by Be. The FMR experiments provide a direct measure of cubic and uniaxial magnetic anisotropy fields, and their dependence on the doping level. It is found that the increase in doping -- in addition to rising the Curie temperature of the Ga${}_{1-x}$Mn${}_x$As layers -- also leads to a very significant increase of their uniaxial anisotropy field. The FMR measurements further show that the effective $g$-factor of Ga${}_{1-x}$Mn${}_x$As is also strongly affected by the doping. This in turn provides a direct measure of the contribution from the free hole magnetization to the magnetization of Ga${}_{1-x}$Mn${}_x$As system as a whole.

11 pages, 4 figures