Surface and 2D magnetism

Abstract

The development of surface science and specifically of spin-polarized electron spectroscopy has been the driving force for a new era of surface and 2D magnetism. Classical primary magnetic quantities such as the temperature dependence of the spontaneous magnetization, the Curie point, the magnetic anisotropies, the variation of the quantum mechanical exchange interaction at clean or modified surfaces, and special surface-induced magnetic structures can now be determined with spin-polarized electron spectroscopies. But a variety of new fields are also appearing, for instance ultrafast time-resolved magnetometry employing laser-induced photoemission of spin-polarized electrons, and imaging of magnetic domains with unprecedented spatial resolution via spin-polarized cascade electrons. Furthermore, by analysing the spin of the photoemitted electrons or by observing the Bremsstrahlung emitted when a spin-polarized electron beam strikes the surface, the majority- and minority-spin electron states in ferromagnets can be investigated separately. Three types of spin-split electron state appear at the surface of a ferromagnet: the bulk magnetic bands, the surface states of Schottky type, and the image potential surface states. With ultrathin ferromagnetic films, magnetometry employing the measurement of the spin polarization of low-energy cascade electrons produces magnificent images of the magnetic domains and reveals the conditions for their occurrence. The dramatic response of the spontaneous magnetization to external disturbances such as an applied magnetic field or an exchange field transferred from a substrate is also obtained. The critical phenomena observed in surface and 2D magnetism fit well into the framework set by the theory many years ago, while the theoretically predicted exotic 2D ferromagnetism in elements that do not exhibit magnetism in 3D has not yet been verified beyond doubt.