Anomalous and planar Hall effect measurements of freely suspended GaMnAs epilayers

Abstract

Strain, a deformation representing the relative displacement between particles in a material body , has emerged a novel parameter in spin-based physical phenomena. In GaMnAs thin film, magnetic anisotropy of the film is strongly influenced by strain built-in during pseudomorphic growth. In order to investigate strain-induced magnetic anisotropy changes as well as magnetic anisotropy at strain-free state, GaMnAs/GaAs/AlGaAs/GaAs structure was grown using UHV-MBE growth, with concentration of Mn ~6% and Al ~ 75%. Freely-suspended GaMnAs structures were fabricated using standard e-beam lithography, with aid of soft metallic electric leads. Freely-suspended structures were in van der Pauw and Hall bar geometry and each sample consist of a freely-suspended structure and a control structure. From temperature dependent longitudinal resistivity, no signs of changes in macroscopic properties nor possible damage during fabrication was observed. From anomalous Hall measurement of van der Pauw structure, in-plane-like magnetic anisotropy of GaMnAs under compressive strain has been modified to more-out-of-plane-like magnetic anisotropy. Further investigation was conducted in anomalous and planar Hall measurement of Hall bar structure. From angle dependent longitudinal and transverse Hall resistance, in-plane magnetic anisotropy from built-in compressive strain is greatly reduced in freely-suspended structures. Utilizing Stoner-Wohlfarth model and non-linear fitting, ratio between in-plane cubic anisotropy and uniaxial anisotropy in freely-suspended structure was estimated to be reduced by 24%. This manipulation of magnetic anisotropy by nano-machining-based strain manipulation suggest possibility of dynamic strain manipulation via nano-machining technique