Angular dependence of spin-transfer switching in a magnetic nanostructure

We measured switching of a thin film nanomagnet driven by spin-polarized current in giant magnetoresistance spin valves as small as 50 nm x 100 nm. Spin-transfer reversal is observed in both dc current and magnetic field sweeps, with a switching current of similar to5 mA, for example, for a bit with similar to900 Oe switching field in zero current. We studied the dependence of spin-transfer switching on the relative angle phi between the layer magnetizations by using a magnetic field to orient the magnetization of a bulk magnetic layer at an angle to a patterned layer held in place by shape anisotropy. The critical current is a minimum for collinear magnetizations and diverges as 1/\cos phi\ as phi increases to 90degrees, consistent with switching current calculations using the Slonczewski spin-transfer torque model. (C) 2003 American Institute of Physics.