Ferromagnetic semiconductors based on III-V compounds, combining semiconductor properties with magnetism, offer also new possibilities for investigation of interesting physical phenomena including the anomalous Hall effect, the so-called planar Hall effect as well as the anisotropic magnetoresistance.

In this paper we report on our recent investigation of the planar Hall effect in 20 nm thick layers of ferromagnetic semiconductor Ga_0.94Mn_0.06As grown by means of low-temperature molecular beam epitaxy on semi-insulating (001)-oriented GaAs substrate. The structures have been subjected to post-growth low-temperature annealing performed under As capping in order to achieve high hole concentration exceeding 10²¹ cm^-3 and high Curie temperature of 135 K. Magnetotransport measurements on lithographically patterned Hall bars of 150 µm width have been carried out at liquid helium temperatures for various orientations of the magnetic field swept up to 1 kOe. The investigated layers exhibit a giant magnitude of the planar Hall effect, which is several orders of magnitude greater than previously found in metallic ferromagnets. It results from the combined effects of strong spin-orbit interaction in the valence band of the zinc blende crystal structure and the large spin polarization of holes in (Ga,Mn)As [1]. When sweeping the magnetic field the effect varies non-monotonously alternating its sign. A characteristic feature of our results has been the appearance of a single or double hysteresis loops in the planar Hall effect data, depending on the magnetic field orientation and the sweeping range of the magnetic field. The results are discussed taking into account the magnetic anisotropy of the (Ga,Mn)As epitaxial layers grown under biaxial compressive strain.

[1] H.X. Tang, R.K. Kawakami, D.D. Awschalom and M.L. Roukes, Phys. Rev. Lett. 90, 107201 (2003)

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