Magnetic properties of Fe-based alloys

The magnetic properties of fcc FexNi1-x and FexCo1-x alloys grown on Cu(100 ) were investigated in an element-specific fashion. The technique employed was linear dichroism in photoemission, which by varying the chirality can a lso determine the magnetization axis. We observed a different behavior for the two alloys at Fe concentrations above 60%. At this concentration the Fe xNi1-x alloy shows a strong reduction of the Fe dichroism associated with t he invar instability. This is in contrast to the FexCo1-x alloy, where the Fe dichroism stays essentially constant across the concentration. Despite t hese differences both systems show a change of the easy axis at roughly the same electron count. For small Fe concentrations the easy axis is in-plane along the [011] direction. This changes into the [001] direction at Fe63Ni 37, which is at 0.7 excess electrons per atom when compared with Fe. This i s different to the bulk, where a change occurs at Fe25Ni75. We find the eas y axis change for FexCo1-x to occur at 49% Fe. This would be equivalent to 0.5 excess electrons when compared with Fe. (C) 2000 American Institute of Physics. [S0021-8979(00)90208-1].