Exchange coupling in epitaxial Fe/Mn/Fe structures

David Tulchinsky
Electron and Optical Physics division

Interlayer exchange coupling through a Mn spacer layer in Fe/Mn/Fe(100) epitaxially grown structures on Fe whiskers shows significantly different behavior than observed with Cr, Ag, or Au spacer layers. The epitaxial growth and sample quality are monitored with in situ RHEED and Auger analysis. For Mn grown in a wedge structure, coupling directions and magnitudes are measured as a function of Mn layer thickness using scanning electron microscopy with polarization analysis (SEMPA) and magneto-optic Kerr microscopy. In the bare Mn/Fe(001) samples, oscillations with a period of 1mL are observed in the secondary electron polarization from the first and second mL of Mn. These polarization oscillation are consistant with in-plane antiferromagnetic ordering (1). Beginning with the fifth monolayer, oscillation in the secondary electron polarization with a 2mL period are measured in the bare Mn/Fe(001) samples, indicating the growth of a wedge with antiferromagnetically aligned Mn layers on top of the Fe whisker. In the Fe/Mn/Fe trilayer structures, beginning at the fourth monolayer of Mn, the coupling is mainly biquadradic (i.e. at 90 deg) -- however a 2mL period ~+/-10 deg oscillation about 90 deg is seen in the magnetization of the top Fe layer indicating an additional weak bilinear coupling. Understanding this biquadradic structure is complicated by the presence of micron sized domains. Unlike earlier work (2), no 180 deg. antiferromagnetic alignment is detected at any Mn layer thickness in the Fe/Mn/Fe(001) structures.


(1) R. Wu and A. J Freeman, Phys. Rev. B 51, 17131 (1995); R. Wu and A. J Freeman, J. Magn. Magn. Mater. 161, 89 (1996).
(2) S. T. Purcell et al., Phys. Rev. B 45, 13064 (1992).