Interface structure and perpendicular exchange bias in (Co∕Pt)n∕FeMn multilayers

Abstract

We have performed a critical experimental evaluation of the dependence of both perpendicular magnetic anisotropy and exchange bias on the structure of the ferromagnet (FM)/nonferromagnet and FM/antiferromagnet interfaces of (Co∕Pt)n and (Co∕Pt)n∕FeMn multilayers. The growth of these heterostructures by ion-beam sputtering was optimized and the characteristics of their interfaces were systematically controlled by varying the ion-beam energy from 250 to 1500 eV. Calculated effective anisotropy constants and exchange bias fields from hysteresis loops were correlated with both structural roughness and the degree of interdiffusion measured by x-ray reflectivity. Whilst the physical roughness remained unchanged, the degree of interdiffusion was found to increase with higher ion-beam energy—concurrently the magnetic anisotropy changed from perpendicular to in plane—leading directly to a decrease in exchange bias and coercivity.