Positive exchange biasing in GdFe/NiCoO bilayers with antiferromagnetic coupling

For GdFe/NiCoO bilayers after field cooling, hysteresis loops at low temperatures are shifted along both the horizontal and vertical axes. The exchange field HE changes from negative values to positive values with increasing cooling field HCF and the coercivity HC acquires a maximum near the crossover of HE. At 5 K, HE and HC at HCF =3 T and the peak height Δ HC are proportional to the inverse GdFe layer thickness. At HCF =3 T, HE is always positive in the temperature region from 5 to 350 K. At low HCF, however, HE is negative at low temperatures and becomes positive at high temperatures. These results can be ascribed to antiferromagnetic coupling between GdFe and NiCoO layers.