Chiral asymmetry driven by unidirectional magnetic anisotropy in spin-orbitronic systems

Spin-Orbit (SO) effects of a ferromagnetic (FM) layer can be artificially modified by interfacial exchange coupling with an anti-ferro magnet (AFM). Non-symmetric magnetization reversals as well as asymmetric transport behaviors are distinctive signatures of the symmetry-breaking induced by such interfacial coupling. We present a complete picture of the symmetry of the SO effects by studying the magneto-transport properties of single FM film and FM/AFM systems (exchanged-biased bilayer and spin-valve structures) with specific in-plane magnetic anisotropy. Single FM films with a well-defined (two-fold) uniaxial magnetic anisotropy display symmetric magnetization reversals and magneto-resistance responses for any value and direction of the applied magnetic field. On the contrary, in the exchange-biased structures, the exchange interaction at the interface between the FM and AFM layers is responsible of chiral asymmetries in magnetization reversal pathways as well as in the magneto-resistance behaviors. Such asymmetries are directly related to the additional unidirectional (one-fold) magnetic anisotropy imposed by the AFM. In particular, chiral reversals and MR responses are found around the magnetization hard-axis direction. This has been shown in FM/AFM bilayer and spin-valve (where the MR outputs are related to different transport phenomena, i.e. anisotropic magneto-resistance and giant magneto-resistance respectively), hence indicating that the chiral asymmetries are intrinsic of systems with unidirectional anisotropy.