The magnetic state of epitaxial overlayers of Mn grown on Fe(100) is s
tudied using spin-polarized electron energy loss spectroscopy. Nonzero
exchange asymmetries are found, demonstrating that the surface layer
of the Mn overlayers has a net magnetic moment. The exchange asymmetry
oscillates with a period of about two atomic layers as the Mn overlay
er thickness is varied, proving that the Mn forms ferromagnetic (100)
sheets and that the sheets align antiferromagnetically. The average Mn
exchange splitting is found to be 2.9 eV, indicating a magnetic momen
t of the order 3mu(B).