Spin reorientation transition in FexNi1-x alloy films

Ni-Cu[100] films display an "unusual" reorientation as a function of thickness, where the magnetization rotates from an in-plane to an out-of-plane orientation upon increase of the thickness. On the other hand, Fe-Cu[100] films show an "usual" reorientation transition where the magnetization rotates from a an out-of-plane to an in-plane orientation if the thickness is increased. We have studied the crossover between the different reorientation behavior by preparing Fe_xNi_1-x-Cu[100] alloys in ultrahigh vacuum (UHV) and studied the magnetic properties with in situ magneto-optic Kerr effect (MOKE). For Ni-rich alloy films, we find that the critical thickness d_c ("unusual transition") is a very sensitive function of the alloy concentration. Starting with d_c = 8.5 ML for Ni-Cu[100], we obtained a value of d_c ∼ 20 ML for Fe_5.6M_94.4. These results can be explained on the basis of elastic and magnetoelastic properties of bulk Fe_xNi_1-x alloys. Beyond this Fe concentration, we could not observe any reorientation, the magnetization stayed in the plane. At ∼ 35% Fe we could observe an "usual" transition at ∼ 1.9 ML for a sample temperature of 110 K. This value increased to ∼ 3 ML for Fe₇₂Ni₂₈, beyond this concentration, we could observe "magnetic live surface layers.".