Point contact studies of rare earth-transition metal compounds

Abstract

Mechanical point contact techniques have been used to study the spin-dependent properties of rare earth-transition metal compounds and transition metal thin films and bi-layers. The transport spin polarisation of Cu, Co and Fe has been measured using point contact Andreev reflection (PCAR), and found to be in good agreement with previous results. In addition, bi-layers of Co/Y and Co/Cu have been used to demonstrate suppression of the spin polarisation of the Co underlayer via a nonmagnetic capping layer. The spin diffusion length of Cu has been estimated to be larger than 600nm. The spin polarisation of molecular beam epitaxy (MBE) deposited RFe2 (R = Dy,Y,Er) Laves phase intermetallic films was determined, and found to be close to that of Fe. This suggests that the spin transport behaviour in these materials is dominated by the Fe sub-lattice. Preliminary evidence for spin transfer torque effects in an RFe2 multilayer and tri-layer is also presented and discussed. Point contact measurements of an ErFe2/YFe2 multilayer at 4.2K show a step in the differential resistance at a positive current value. It is suggested that this is due to the formation of a nano-domain beneath the tip. Measurements of a DyFe2/YFe2/DyFe2 tri-layer show peaks in differential resistance for negative applied currents. This is tentatively attributed to the generation of spin waves within the YFe2 layer.

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