Studies of magnetization reversals about two kinds of MR curves observed in the spin valve using the (110) magnetite pinning layer

Abstract

In the spin valves composed of Co/Cu/Co on the epitaxial (110) Fe3O4 as the pinning layer, we found out that shapes of magnetoresistance (MR) curves depended on thickness of the cobalt pinned layer (PL) with the field applied in the 〈110〉 direction of Fe3O4: (1) the flat-shaped MR curve showed low MR ratio under 2nm thickness of cobalt pinned layer (PL): (2) the unusually shaped MR curve showed high MR ratio over 5nm thickness of PL in spite of the hard direction of Co layers. We assumed that the synchronous magnetization reversal (SR) of PL and Fe3O4 would occur at the MR switching field due to 90° coupling between PL and Fe3O4 layers. Then, only occurrence of SR of PL cause the drastic change of the magnetization relative angle between FL and PL, indicating the observation of the unusually shaped MR curve having high MR ratio. On the other hand, the SR of cobalt free layer (FL) together with the PL flip also occur due to the large contribution of Néel-type ferromagnetic coupling between FL and PL, which lead to less changing the relative angle of FL and PL during magnetization processes, indicating the observation of a flat-shaped MR curve having low MR ratio. This dependence of PL thickness on MR curves might come from the balance of Néel (ferromagnetic) and stray field (antiferromagnetic) coupling due to magnetic free pole at edge of PL.