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.