Ferromagnetic, Ferrimagnetic and Spin-wave Resonances in GaMnAs Layers

Molecular beam epitaxy grown Ga$\text{}_{1-x}$Mn$\text{}_{x}$As layers were investigated by means of magnetic resonances. With an increase in Mn concentration, x, the spectrum changes from the (i) paramagnetic one, with resolved fine and hyperfine structures, typical of S=5/2 spin of substitutional Mn$\text{}^{2+}$ ions, for very diluted alloy, via (ii) paramagnetic spectrum, where the fine and hyperfine structures are averaged by a long range Mn$\text{}^{2+}$-Mn$\text{}^{2+}$ exchange coupling, (iii) single, isotropic line of ferromagnetic resonance. Insulator to metal transition is accompanied with occurrence of (iv) a very complex spectrum of the ferrimagnetic resonance, accompanied with the well-resolved spin wave resonance. Reentrance to insulator phase for the most condensed alloys is accompanied with the reentrance to (v) ferromagnetic phase. The data confirm that the effective mass holes transfer the exchange interaction between localized Mn$\text{}^{2+}$ spins.