Competition between direct exchange and indirect RKKY coupling in Fe/V[001] superlattices

Fe 10 Å /V t
_V
(001) superlattices are prepared by magnetron sputter deposition and characterized using x-ray diffraction (XRD), magneto-optical Kerr effect (MOKE) magnetometry, and x-ray magnetic circular dichroism (XMCD). MOKE loops show three peaks in saturation field as a function of t
_V
, indicating RKKY induced AF coupling at t
_V
=22 Å, 32 Å, and 42 Å. The expected AF coupling peak at 12 Å, however, is missing. XMCD measurements show that the V layers carry a relatively large magentic moment which extends surprisingly far from the Fe/V interface. Such 'transient ferromagentism' suggests a strong V-V direct exchange coupling within the V layer. We argue that the V-V direct exchange coupling suppresses the 12 Å AF coupling peak, but since direct exchange coupling decays more quickly than RKKY coupling, the AF peaks at 22, 32, and 42 Å are observed.