Coherent Spin-Dependent Tunneling and Giant TMR Effect in Magnetic Tunnel Junctions with a Crystalline MgO Tunnel Barrier

Abstract

A magnetic tunnel junction (MTJ), which consists of an ultrathin insulating layer (a tunnel barrier) sandwiched by two ferromagnetic electrode layers, exhibits tunnel magnetoresistance (TMR) effect due to spin-dependent electron tunneling. Since the discovery of room-temperature TMR effect in 1995, extensive studies have been made on MTJs with an amorphous aluminumoxide (Al-0) tunnel barrier, which exhibit magnetoresistance (MR) ratios of up to 70% at room temperature (RT). However, these relatively small MR ratios were considered to severely limit the feasibility of spintronic device applications. Fortunately, novel MTJs with a crystalline magnesium-oxide (MgO) tunnel barrier were developed recently and found to exhibit giant MR ratios above 400% at RT. In this article, we introduce recent studies on physics and applications of coherent spin-dependent tunneling in MgO-based MTJs.