Magnetic and structural properties of interfaces

Abstract

Metallic magnetic multilayers have attracted considerable interest in basic as well as applied research during the last decade. This is due to the development of powerful new experimental tools in surface and thin film physics and to the advances in the preparation of artificially layered ultrathin coherent structures and superlattices. In particular, two recently observed effects which are based on the existence of interfaces, gave a large impact to this field. The first effect is the magnetic interlayer coupling detected in the Fe /Cr /Fe film system [1]. Depending on the thickness of the Cr interlayer, the magnetization of the two Fe films can be ferromagnetically (FM), or antiferromagnetically (AFM) aligned, or it can be rotated by 90 ~ The effect is explained by a RKKY-type interaction across the nonmagnetic interlayer. A convenient tool for the investigation of these phenomena is the magneto-optic Kerr effect (MOKE). The second effect is the giant magnetoresistance in such AFM coupled structures [2] implying a strong potential for technical applications for magnetic sensors and reading heads. Due to the different scattering probability for conduction electrons at interfaces between FM or AFM aligned films, the electrical resistance of such film structures changes considerably in an external magnetic field. Both effects depend strongly on the magnetic interactions and on the roughness of the interfaces. For systems containing Fe films CEMS is a unique tool for the investigation of those properties [3,4]. By inserting a 57Fe probe layer of one to three monolayers (ML) thickness at different positions in the the fdm sample one can determine the magnetic hyperfine (h0 field Bhf as a function of distance from an interface with ML resolution. In this way, theoretical predictions of the Bhf behavior near interfaces as obtained by band structure calculations can be checked experimentally. Furthermore, as a function of temperature, the local hf field at interfaces usually follows a T 3/2 spin wave law. From such temperature dependences the spin wave parameter b can be derived providing information on the local exchange interactions. On the other hand, besides LEED, RHEED [5] and X-ray scattering with grazing incidence, CEMS can be used for an analysis of the microroughness at interfaces on a nm scale. By inserting a 2 ML thick 57Fe probe layer directly at the interface the resulting CEM spectrum is a superposition of various