Magneto-optical spectra of Fe/Au artifical superlattices modulated by integer and noninteger atomic layers

Spectra of the magneto-optical Kerr effect, in a series of [Fe (xML)/Au (xML)]_N superlattices with integer and noninteger values of x (1≤x≤15), were measured. For x = 1 the superlattic forms an L1₀-type ordered alloy structure. The magneto-optical spectrum of the superlattice exhibits a prominent structure around 4 eV, which shows a systematic shift toward higher energies as x increases (1≤x≤5). No such structure can be reproduced by an optical calculation assuming a simple stack of thin Fe and Au layers. Ab initio band calculations have shown similar magneto-optical spectra and a similar peak shift with an increase in x (1≤x≤6). This suggests that electronic structures which differ from that of a simple stack of thin Fe and Au are realized in the superlattices. For noninteger values of x, oscillatory behavior with a period of one monolayer was observed in the low energy region of the magneto-optical spectra.