Giant planar Hall effect in ferromagnetic (Ga,Mn)As layers

We have performed a systematic investigation of the so-called planar Hall effect and the magnetization in thin layer of ferromagnetic Ga0.94Mn0.06As semiconductor, which has been subjected to post-growth annealing. The annealing process was performed under As capping in order to achieve high hole concentration exceeding 1021 cm−3 and high Curie temperature of 125 K. At liquid helium temperature the planar Hall effect in the layer exhibits a giant magnitude, several orders of magnitude greater than analogous effect found in metallic ferromagnets. When sweeping the magnetic field the planar Hall resistance varies non-monotonously alternating its sign and displaying the appearance of single or double hysteresis loops, depending on the magnetic field orientation and the sweeping range of the magnetic field. It is demonstrated, by comparing with the magnetization data, that the planar Hall effect reproduces the complex behaviour of the magnetic anisotropy of the layer grown under biaxial compressive strain, which additionally displays uniaxial in-plane magnetization anisotropy.