Magneto-transport properties of GaMnAs:Si ferromagnetic semiconductors

The magnetic properties of a series of GaMnAs:Si ferromagnetic semiconductor films, in which the Mn concentration ranges from 7% to 10%, were investigated by using magneto-transport measurements. The temperature dependence of the resistivity revealed a systematic increase in the Curie temperature (T_c) with increasing Mn concentration in the series. Since the T0 of the undoped GaMnAs ferromagnetic semiconductor decreases with increasing Mn concentration above 6%, the observation of a systematic increase of T _c with increasing Mn concentration in our GaMnAs:Si series indicates the effectiveness of our counter doping for the incorporation of a a large amount of 7% Mn in the system. The field scan of the planar Hall effect (PHE) showed a typical two-step switching behavior at low temperatures, indicating the presence of a strong cubic anisotropy. The switching fields, however, systematically decreased with increasing Mn concentration in the series. The angular dependences of the switching fields were fitted by using the magnetic free energy and Cowburn's model to obtained the domain pinning energy, which showed systematically smaller values as the Mn concentration of the sample was increased. The temperature dependences of the pinning energies indicated a change in the uniaxial anisotropy from the [110] to the [110] direction with increasing Mn concentration in the series.