Towards Antiferromagnetic Metal Spintronics

Spintronics in ferromagnetic systems is built on a complementary set of phenomena in which the magnetic configuration of the system influences its transport properties and vice versa. Giant magnetoresistance (GMR) and spin transfer phenomena are typical examples of such interconnections found in ferromagnetic (F) multilayers. Recently, MacDonald and co-workers predicted that corresponding effects ought to occur in antiferromagnetic (AFM) multilayers where F components are replaced by AFMs. First, it was predicted that resistance of an AFM spin valve-here two AFM layers are separated by a nonmagnetic (N) spacer-could depend upon the relative orientations of magnetic moments in the two AFM layers (antiferromagnetic GMR). Second, injection of a strong enough current density into an antiferromagnet was predicted to affect its magnetic state; in particular, they predicted current-driven variations in exchange bias in F/AFM metal pairs. These new AFM effects may potentially lead to a new all-antiferromagnetic spintronics where antiferromagnets are used in place of ferromagnets. We and others have recently provided experimental evidence of current-driven effects on exchange bias at F/AFM interfaces. This talk will focus upon our experiments which demonstrated for the first time that the exchange bias is affected by an electrical current of high density (~10¹² A/m²) flowing across the F/AFM interface. We find that, depending on the polarity of the current, the strength of the exchange bias can either increase or decrease. To explain our findings we exploit the theoretical prediction that the current mediates the transfer of spin angular momentum to AFM metal and generates a torque on its magnetic moments. Such a current-mediated variation of exchange bias could be used to control the magnetic state of spin-valve devices, e.g., in magnetic memory applications. I will also discuss our search for antiferromagnetic GMR in systems containing two AFMs separa- - ted by a non-magnetic (N) metal spacer.