Antiferromagnetic interlayer coupling in epitaxial Fe/EuS (100) bilayers (abstract)

Abstract

We present the observation of antiferromagnetic interlayer coupling between two ferromagnetic layers of Fe(100) and EuS(100), which are in direct contact. The coupling strength J is about 0.2 mJ/m2 at 5 K, it decreases with increasing tempeature and becomes negligibly small near the Curie temperature of the EuS layer. The samples were molecular-beam epitaxy-grown on the GaAs(100) single crystal substrates using a silver buffer layer. The structural and chemical properties of the layers were characterized by in situ low-energy electron diffraction and Auger electron spectroscopy and by ex situ Rutherford backscattering. Superconducting quantum interference device (SQUID) magnetometry was used for measurements of the absolute magnetic moments as a function of temperature or magnetic field. Hysteresis measurements were performed by means of the magneto-optical Kerr effect (MOKE). We found evidence of antiferromagnetic coupling between the two different ferromagnetic layers both from zero field cooling experiments through Tc(EuS) as well as directly from the shape of the hysteresis loops at low temperatures. The temperature dependence of the interlayer coupling strength shows that J is proportional to the EuS magnetization. The observed onset temperature of ferromagnetic order in EuS is up to three times higher than the Curie temperature of bulk EuS. We discuss a mechanism in which this enhancement is connected to the existence of structural defects in the EuS film, caused by the growth. The defects produce additional band carriers, which in turn enhance the Curie temperature of the layer due to a very large indirect s(d)–f exchange.