Linear Magnetic Dichroism in Directional Photoemission from Core Levels and Valence Bands

The need for new surface specific probes of magnetism is very high. The ideal surface magnetic probe should be selectively sensitive to surface, subsurface and interface layers, atom-specific and site specific, i.e. sensitive to the local environment of the excited atom, an should provide an absolute measure of the magnetic moment associated to the selected atoms. The field of surface magnetism has been opened by the application of spin-polarimetry to photoelectrons and to the secondary electron yield.[1] The measure of spin polarization (SP) of secondaries is intrinsically surface sensitive due to the short escape depth for low energy photoelectrons in ferromagnets, and can be understood semi-quantitatively.[2] The magnetic resolution of SP is high and can be used for imaging surface magnetic domains[3] and for studying the dynamics of surface magnetism with time resolution in the picosecond range in laser experiments,[4] or in the nanosecond range in synchrotron radiation experiments.[5] SP of secondaries probes the average magnetization and cannot be made atom-specific without independent knowledge on the atomic structure. [6] Spin Polarized Low Energy Electron Diffraction is very surface sensitive,[7] but it is limited to ordered surfaces, and is not atom specific. The magneto-optic Kerr effect [8] is not surface sensitive and can be applied only to the study of ferromagnetic order in monolayers on non magnetic substrates.