Magnetoresistive devices based on epitaxial NiMnSb layers with built-in anisotropy

We have fabricated tunnelling magnetoresistance (TMR) devices based on an epitaxial layer of NiMnSb grown almost lattice matched on (In,Ga)As, an aluminium oxide barrier and a CoFe counter electrode. The devices show a TMR of 14% at low temperature and 8% at room temperature. The as-grown NiMnSb layer exhibits a strong uniaxial anisotropy, which leads either to a clean spin valve signal with layers that switch separately and in single steps when the field is applied along the easy axis of the material, or to a resistance which varies linearly with B-field when the field is applied along the hard axis of the Heusler layer. Giant magnetoresistance (GMR) devices have also been fabricated, using sputter deposition of a Cu interlayer onto the NiMnSb and subsequent deposition of CoFe. Devices fabricated this way exhibit a magnetoresistance of 3.5% at room temperature. Depending on the thickness of the interlayer no coupling or a strong antiferromagnetic coupling can be observed.