Highlights 2002

Modern magnetic materials are often composed of several elements, each of which contributes in a specific manner to the global magnetic properties. In order to understand the magnetic behavior of a complex compound on the basis of its constituents, the magnetic state of an individual sort of atoms must be determined. Such an element-selective probing of magnetic atoms can be conveniently achieved by x-ray magneto-optical (MO) spectroscopies. As a consequence, these spectroscopies have developed into leading-edge research techniques for the investigation of magnetism. The continuously increasing access to brilliant and polarized synchrotron radiation has also considerably boosted the popularity of magneto-x-ray spectroscopies. One particular magneto-x-ray spectroscopy that has become widely exploited of late, is the x-ray magnetic circular dichroism (XMCD). Element-specific information about the spin-polarized electronic structure of ferromagnetic (FM) atoms can superiorly be accessed by the XMCD. The demonstration of the anisotropy of the orbital moment and its relationship to the magnetocrystalline anisotropy energy belongs to one of the recent outstanding achievements accomplished by employing the XMCD [1]. XMCD and related spectroscopic techniques have furthermore been applied to image anomalous ferromagnetic domain structures [2]. While the spin-polarized electronic structure of FM’s can be probed by XMCD and related techniques, no comparable spectroscopy has been available for antiferromagnets (AFM). Among the magnetic materials of current technological interest, AFM’s have gained appreciable importance lately. Antiferromagnetic materials find key applications in novel spintronic devices, such as magnetoresistive, tunneling magnetoresistive, or other exchange-biased microstructures and nanostructures [3]. In these devices, that often comprise embedded AFM layers exchange-coupled to FM layers, the spin-polarized electronic structure of the AFM’s plays an important role. Surprisingly, there exists practically no experimental knowledge of the AFM spin-resolved electronic structure up to now. This is related to the inability of traditional techniques to spinsensitively probe the antiferromagnetically ordered electronic state. Various research initiatives in this direction have recently been undertaken. Only MO spectroscopies that are sensitive to the square of the local magnetization M are successfully applicable to AFM’s. The recently observed x-ray Voigt effect, measured in transmission belongs to these spectroscopies [4], and the x-ray magnetic linear dichroism (XMLD), which is either measured in transmission or in absorption by the total yield of Peter M. Oppeneer, Jan Kunes, Michael Hecker, Claus M. Schneider, Stepka Zotova, Rainer Kaltofen A novel spectroscopy X-ray magneto-optical spectroscopy of buried antiferromagnetic films: Theory and experiment