Inverse MR and Dual-AMR Phenomena in Co/CoO/Ag/Co Sandwiches

Band-form Co/CoO/Ag/Co sandwiches were prepared using radio-frequency magnetron sputtering. The sandwiches had rather thick Co ( t CO = 63 nm) and Ag ( t Ag = 2 ÷ 65 nm) layers and a super-thin paramagnetic cobalt monoxide (CoO) layer (< 1 nm) inserted in the Co/Ag interface. The sandwiches exhibited anomalous magnetoresistance (MR) behavior depending on the t Ag value. Inverse magnetoresistance (IMR) effect was observed only at thin t Ag values of 2 nm and 6 nm, whereas the dual-anisotropic MR (dual-AMR) occurred at thicker t Ag values of 12 nm, 25 nm and 65 nm. A superposition of the dual-AMR and the weak IMR effects was obtained at the thickest Ag layer of 65 nm. The origin of these anomalous MR behaviors was discussed to show the prominent role of the CoO layer and large thickness of the Co and Ag layers.