PRESENT STATUS OF MAGNETO-OPTICAL EFFECTS

We discuss magneto-optical effects in magnetic materials at various photon-energies. At first we focus on the absorption of circularly polarized X-rays by a ferromagnetic substance. We review, briefly, the experimental observations of this interesting effect and present a first principles, quantitative theory of it. The theory is based on a fully relativistic description of the electronic transitions involved, with the spin polarization and the spin orbit coupling treated on equal footing. We illustrate it with explicit calculations for ferromagnetic Fe. Next, we study the related phenomenon of magneto-optic Kerr effect in the visible range of frequencies. We note the technical significance of this phenomenon in connection with read-out processes in magnetic storage devices and develop a theoretical description of it on the basis of relativistic quantum mechanics. We follow closely our treatment of the simpler X-ray absorption problem. However, the calculations are rendered tractible by using our recently developed, spin-polarized, relativistic LMTO method of band structure calculation. The first results are compared with other calculations as well as with experiments.