Spin dependent tunneling junctions with reduced Neel coupling

Abstract

A new structure of spin dependent tunneling (SDT) junctions has been demonstrated to have a much reduced Neel coupling field between the free and pinned ferromagnetic layers comparing with conventional SDT structures. The new structure consists of a modified synthetic-antiferromagnetic composite layer as the pinned layer with two Ru spacer layers and three ferromagnetic layers. The Neel coupling field is much reduced for both top- and bottom-pinned SDT structures using this new composite pinned layer. Furthermore, the net magnetic moment is kept at zero for the composite pinned layer to minimize the fringe field after patterning. The coupling reduction can be understood by considering the additive contribution from the first two interfaces with Ru in the composite pinned layer, which cancels that from the pinned layer interface with the barrier. By properly spacing these three most important interfaces, reducing the coupling to basically zero is realized. The coupling reduction allows the elimination of an on-chip bias coil used to correct the coupling, therefore simplifying the electronics and reducing the power to operate the SDT sensors. The new SDT structure has potential impacts on many SDT and spin valve devices such as magnetoresistive sensors, galvanic isolators, magnetic logic, and MRAM devices.