Unusual magnetic phases in MnCo ultrathin alloy films

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. All rights reserved.