Temperature dependence of exchange field and coercivity in polycrystalline NiO/NiFe film with thin antiferromagnetic layer: Role of antiferromagnet grain size distribution.

The temperature dependence of the exchange bias H[sub eb] and coercivity H[sub c], has been measured for a NiO(6.5 nm)/Ni[sub 81]Fe[sub 19](12 nm) bilayer which demonstrated at room temperature zero exchange bias, but an enhanced coercivity (H[sub c]=65 Oe). Upon cooling the sample in a magnetic field (H=300 Oe), the exchange bias remains zero down to T=250 K, whereas the coercivity increases roughly linearly with decreasing temperature. Below this critical temperature an exchange shift of the hysteresis loop occurs that is accompanied by a decrease in the coercivity. Decreasing the temperature further results in an increase in both H[sub eb] and H[sub c]. A thermal fluctuation model, where both fluctuating and stable AF grains contribute to the coercivity, with an additional assumption of increasing the density of NiO interfacial uncompensated spins at low temperature, predicts the correct temperature behavior of H[sub eb] and H[sub c]. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]