Non-collinear exchange coupling in Fe/Mn/Fe(001): insight from scanning tunneling microscopy

The film growth and morphology of epitaxial Mn films grown on Fe(001) singl e-crystal whiskers measured with scanning tunneling microscopy (STM) provid es insight into the mechanism of interlayer exchange coupling in Fe/Mn/Fe(0 01) trilayers. The proximity model of Slonczewski for exchange coupling thr ough an antiferromagnet predicts that the coupling angle between the ferrom agnetic layers will oscillate around a mean value of 90 degrees with an amp litude that is very sensitive to the width of the thickness distribution of the spacer layer. We measure the thickness distribution with the STM and f ind that the coupling angle variation predicted by the proximity model is q ualitatively consistent with the actual coupling angle variations in Fe/Mn/ Fe(001)measured with scanning electron microscopy with polarization analysi s (SEMPA). Going beyond the proximity model and allowing for a non-uniform magnetization of the thin Fe overlayer provides an improved explanation of the results. We contrast the behavior of Fe/Mn/Fe(001),where the proximity model appears applicable, to coupling through antiferro-magnetic Cr in Fe/C r/Fe(001), where it is not, and discuss possible reasons for the difference . (C) 2000 Elsevier Science B.V. All rights reserved.