For over a quarter century the Mn:Co magnetic phase diagram has been contro
versial. We find that for Mn:Co ultrathin alloys with dilute Mn concentrati
on, the Mn and Co moments are coupled parallel for dilute Mn concentrations
using X-ray magnetic circular dichroism (XMCD), in contradistinction to th
e latest accepted bulk results using neutron scattering. To determine if th
e parallel coupling was the result of epitaxial strain, surface or interfac
e effects, we also performed measurements on very thick films of the same c
ompositions. XMCD shows that thick him Mn : Co alloys have identical magnet
ic coupling as ultrathin films. (C) 1999 Published by Elsevier Science B.V.
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