Anomalous temperature dependence of interlayer coupling in Fe/Si multilayers (abstract)

Abstract

The magnetic coupling of the Fe layers in Fe/Si multilayers strongly depends on the morphology of the iron-silicide interlayer that forms during deposition. Antiferromagnetic interlayer coupling is only observed in Fe/Si multilayers with crystalline interlayers in the CsCl structure. Recently, it has been shown that single layers of Fe–Si in the CsCl structure can be grown epitaxially on Si over a range of stoichiometries. FeSi films are reported to be Kondo insulators below 50 K. We find evidence of a magnetic phase transition in antiferromagnetically coupled Fe/Si multilayers. Ms measured in a constant applied field of 50 kOe shows T3/2 behavior down to 10 K. However, M(T) at a lower constant field peaks around 50 K and decreases at lower temperature, indicating enhanced antiferromagnetic coupling or a phase transition. The remanent magnetization increases monotonically with decreasing temperature and has been explained by invoking thermally activated coupling. However, the saturation field also increases with decreasing temperature, indicating a stronger antiferromagnetic interaction. We explore the suggestion that the interlayer coupling is biquadratic in nature. Polarized neutron reflectometry has also been used to get a clearer picture of the complicated magnetic behavior of this multilayer system.