We explore the magnetic anisotropy of GaMnAs ferromagnetic semiconductor by Planar Hall Effect (PHE) measurements. Using low magnitude of applied magnetic field (i.e., when the magnitude H is smaller than both cubic Hc and uniaxial Hu anisotropy field), we have observed various shapes of applied magnetic field direction dependence of Planar Hall Resistance (PHR). In particular, in two regions of temperature. At T < Tc/2, the "square-shape" signal and at T > Tc/2 the "zigzag-shape" signal of PHR. They reflect different magnetic anisotropy and provide information about magnetization reversal process in GaMnAs ferromagnetic semiconductor. The theoretical model calculation of PHR based on the free energy density reproduces well the experimental data. We report also the temperature dependence of anisotropy constants and magnetization orientations. The transition of easy axis from biaxial to uniaxiale axes has been observed and confirmed by SQUID measurements.
The magnetic field dependencies of Hall resistance are studied for Ga 0.94 Mn 0.06 As/In 0.15 Ga 0.85 As film. The Hall resistance shows a slanted hysteresis cycle, emphasizing the existence of both in-plane and out-of-plane magnetization components. The anisotropy constants of the sample with out-of-plane magnetization are extracted from the angular dependence of Hall resistance measurements. The angular dependence of free magneto-crystalline energy theoretical analysis allows us to confirm the dominance of uniaxial magnetic anisotropy at specific temperatures. Here, precise angular dependence of magnetoresistance Hall Effect measurements and careful analysis using free energy model, enable us to demonstrate how the magnetic easy axis could be reoriented by the temperature within the ferromagnetic phase at the temperature far from the Curie Weiss value. This promising property will offer applicative opportunity of GaMnAs material with temperature induced transition of easy magnetization axis in detection of weak magnetic fields within the cryogenic range of low temperature phenomenon.
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