Size effects on exchange bias in sub-100 nm ferromagnetic–antiferromagnetic dots deposited on prepatterned substrates

Abstract

Exchange bias effects have been investigated in ferromagnetic (FM)–antiferromagnetic (AFM) square dots, with lateral sizes of 90 nm, sputtered on a prepatterned Si substrate. The magnetic behavior of the dots has been compared with that of a continuous FM–AFM bilayer with the same composition. Along the unidirectional direction, the dots exhibit square hysteresis loops and preserve an exchange bias field, HE, of 70 Oe at room temperature, which is about 40% smaller than HE in the continuous film. In addition, the distribution of blocking temperatures in the nanostructures is found to be shifted toward lower values with respect to that in the continuous film. These results can be interpreted assuming that the reduced lateral dimensions of the nanostructures impose some constraints on the formation and pinning of domain walls in the AFM layer.