Correlation between Exchange Anisotropy and Crystal Structure of Ferromagnetic Layer in γ-Mn-Ir/Fe-Co-Ni Bilayers

Abstract

The unidirectional anisotropy constant, JK, of γ-Mn-Ir / FM (FM = Fe-Co-Ni) bilayers was investigated by systematically changing the composition of the Fe-Co-Ni layers. The FM layers were grown in the crystal structures corresponding to their composition on the (111)-oriented face centered cubic (fcc) Mn-Ir layer. JK was significantly changed around the phase boundary of the FM layer between the body-centered cubic (bcc) phase and fcc-phase. The experimental results revealed a general feature where bcc-structured FM layers were more likely to induce stronger exchange anisotropy than fcc-structured FM layers. The JK values and the lattice mismatch between the Mn-Ir layer and the FM layer were increased with increasing Co concentration in the bcc-FM region. The dependence of JK on FM composition have been explained qualitatively with lattice distortion at the interface between the Mn-Ir and FM layers.

An atomic model calculation of exchange anisotropy and uncompensated spin element in antiferromagnetic layer: An effect of exchange coupling with various ferromagnetic materials

“…In particular, the Mn-Ir alloy [8] is widely used in magnetic recording systems. From an applications perspective, a large exchange bias was experimentally found in a body-centred-cubic (bcc) FM/Mn-Ir system that was larger than that in a face-centredcubic (fcc) FM/Mn-Ir system [9,10]. Much experimental and theoretical effort has been devoted to understanding the exchange anisotropy phenomenon [11,12], however, the microscopic origin of the exchange bias remains unclear at this point.…”

“…In experiments, the increment in J K is produced by increasing the Co content in the bcc-FeCo alloy [9,10]. This corresponds to increasing the electron density of the 3d orbitals.…”