Angular dependence of the exchange bias direction and giant magnetoresistance on different cooling-field strengths

Abstract

We studied the effect of different cooling-field strengths on the exchange bias by measuring the angular-dependent sheet resistance and the giant magnetoresistance of exchange-biased spin valves using a PtMn antiferromagnetic and a synthetic antiferromagnetic layer. When we annealed the spin valve at a cooling-field of 100 Oe, the exchange bias was antiparallel to the cooling-field. As we increased the cooling-field to 4000 Oe, the exchange bias direction gradually rotated and it ended up parallel to the cooling-field direction. The giant magnetoresistance also changed with the cooling-field strength. In the cooling-field range between 100 and 4000 Oe, the magnetoresistance ratios measured along the cooling-field direction were significantly reduced. However, the magnetoresistance ratios measured along the exchange bias direction increased, although still remaining smaller than those of the spin valve annealed at 100 or 4000 Oe. On the other hand, the exchange bias strength did not change significantly with the cooling-field strength.