Magnetic moments, coupling, and interface interdiffusion in Fe/V(001) superlattices

Epitaxial Fe/V(001) multilayers are studied both experimentally and by theoretical calculations. Sputter-deposited epitaxial films are characterized by x-ray diffraction, magneto-optical Kerr effect, and x-ray magnetic circular dichroism. These results are compared with first-principles calculations modeling different amounts of interface interdiffusion. The exchange coupling across the V layers is observed to oscillate, with antiferromagnetic peaks near the V layer thicknesses $t_V\approx 22$, 32, and 42 Å. For all films including superlattices and alloys, the average V magnetic moment is antiparallel to that of Fe. The average V moment increases slightly with increasing interdiffusion at the Fe/V interface. Calculations modeling mixed interface layers and measurements indicate that all V atoms are aligned with one another for $t_V\lesssim 15$ Å, although the magnitude of the V moment decays toward the center of the layer. This “transient ferromagnetic” state arises from direct $(d$-$d)$ exchange coupling between V atoms in the layer. It is argued that the transient ferromagnetism suppresses the first antiferromagnetic coupling peak between Fe layers, expected to occur at $t_V\approx 12$ Å.