GaMnAs ferromagnetic semiconductor films under compressive strain are characterized by strong biaxial in-plane anisotropy, which generates four stable magnetization directions at zero magnetic field. This feature results in double switching behavior during magnetization reversal process measured by planar Hall resistance (PHR). Minor scans of the PHR exhibit staggered asymmetric loops due to the formation of stable muti-domain structures. We show that the resulting four stable PHR states can serve as quaternary logic states for a spin memory device.
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