Inverse giant magnetoresistance in rare-earth/transition metal multilayers

Giant magnetoresistance (GMR) is observed in multilayered structures with 3 d ferromagnetic layers separated by normal metal spacer layers, and is usua lly a negative magnetoresistance. No GMR has been observed to date in multi layers with solely 4f ferromagnetic layers. Nevertheless, in a hybrid 3d/4f magnetic multilayer of the form {Co/Dy/Co/Cu/Co/Cu} x N an inverse GMR of up to -6.5% has been measured at 4.2 K. This effect. is explained in terms of a spin-engineered configuration of layers which forces the moments of ad jacent Co layers to be anti-parallel in a high-field state, and parallel in a low-field slate. Since the structure is formed from separate magnetic la yers, it has been shown, by varying the order of the layers, that Co/Cu int erfaces are essential to the GMR in these types of structures. Although the re is no GMR in rare-earth/non-magnetic multilayers, the Dy layers aye suff iciently transparent to electrons for the GMR to continue rising as the num ber of repeal units is increased, up to N = 4.