Magneto-transport Properties of GaMnAs:Si FerromagneticSemiconductors

Abstract
The magnetic properties of a series of GaMnAs:Si ferromagneticsemiconductor 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 systematicincrease in the Curie temperature ($T_c$) with increasing Mnconcentration in the series. Since the $T_c$ of the undoped GaMnAsferromagnetic semiconductor decreases with increasing Mnconcentration above 6\%, the observation of a systematic increase of$T_c$ with increasing Mn concentration in our GaMnAs:Si seriesindicates the effectiveness of our counter doping for theincorporation of a a large amount of 7\% Mn in the system. The fieldscan of the planar Hall effect (PHE) showed a typical two-stepswitching behavior at low temperatures, indicating the presence of astrong cubic anisotropy. The switching fields, however,systematically decreased with increasing Mn concentration in theseries. The angular dependences of the switching fields were fittedby using the magnetic free energy and Cowburn's model to obtainedthe domain pinning energy, which showed systematically smallervalues as the Mn concentration of the sample was increased. Thetemperature dependences of the pinning energies indicated a changein the uniaxial anisotropy from the [$overline{1}10$] to the[110] direction with increasing Mn concentration in the series.
Keywords: Ferromagnetic semiconductros, Hall effect, Magnetic anisotropy, Doping

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