Current-induced reorientation of exchange bias on a nanoscale

PAPER: J. Basset, Z. Wei, and M. Tsoi,

“Current-induced reorientation of exchange bias on a nanoscale”,

in preparation

SLIDES: 11^th Joint MMM-Intermag Conference

Washington, DC, January 18-22, 2010

ABSTRACT:

A thin ferromagnetic (F) film adjacent to an antiferromagnet (AFM) is known to possess unidirectional exchange anisotropy, or exchange bias [1], which arises from an exchange interaction between F and AFM moments near the F/AFM interface. Here we demonstrate how local heating by electric current can induce and reorient the exchange bias on a nanoscale. In our experiments we use point contacts ~10 nm in size to inject current densities as high as 10¹⁴ A/m² into F/N/F/AFM exchange-biased spin valves (EBSV) where two F layers are separated by a nonmagnetic (N) metal spacer and one F-layer is biased by an adjacent AFM layer. At low currents the spin valves exhibit the usual giant magnetoresistance (GMR) when two F layers switch from parallel to antiparallel orientation. At high currents (~10¹⁴ A/m²) the Joule heating in the contact becomes significant and in combination with static magnetic field can induce and repeatedly reorient the exchange bias in a small contact volume (10³-10⁵ nm³). Interestingly, the strength of exchange bias induced in the point contact was found to depend on the polarity of applied current. We tentatively attribute this polarity dependence to spin-transfer torques arising near F/AFM interface at high currents [2, 3].

[1] W. H. Meiklejohn, C. P. Bean, Phys. Rev. 102, 1413 (1956).

[2] A. Nunez et al., Phys. Rev. B73, 214426 (2006).

[3] Z. Wei et al., Phys. Rev. Lett. 98, 116603 (2007).

This work was supported in part by NSF Grant DMR-06-45377