Proceedings of Magneto-Optical Recording International Symposium '99, J. Magn. Soc. Jpn., Vol. 23, Supplement, No. SI (1999), pp.21- 26 © 1999 by The Magnetics Society of Japan Theory of the Anisotropic Magneto-Optical Kerr Effect in Artificial FeAu and MnAu and in XAu 4 (X=V, Cr, Mn) Compounds Peter M. Oppeneer, I. Galanakis*, P. James", O. Eriksson··, and P. Ravindran" Institute o.fTheoretical Physics, University afTechnology, D·01062 Dresden, Gennany *Departmem of Physics, University of Strasbourg, F·63037 Atrasbourg, France **Department of Physics. Uppsala Box 530, S· 75112 Uppsa/a, Sweden The magneto-optical Kerr spectra of several transition-metal-An alloys are investigated theoretically, on the basis of relativistic energy-band theory in the framework of the local-spin-density-functional theory. Calculated Ken spectra are presented for the artificial compounds FeAu and MnAu, and also for the ordered XAU4 (X::: V, Cl', Mn) compounds. The theoretical Ken spectra of FeAu correspond in shape to the experimental spectra, but the calculated Kerr effect is bigger than the experimental one. For the XAU4 compounds a modest Kerr angle of -0.4" to -0.5° at, 1.7eV is predicted. The XAU4 compounds are predicted to display a huge Kerr anisotropy, which is purely a magnetocrystaIline anisotropy effect. Key words: energy-band theory, magneto-optical Ken effect, Kerr ani sot ropy, magnetocrystalline anisotropy. 1. Introduction In recent years it has become established that relativistic energy-band theory, based on density- functional theory in the local-spin-density approx- imation (LSDA) [lJ is applicable for the descrip- tion of magneto-optical (MO) phenomena. This has been demonstrated for numerous transition-metal com- pounds, for which ab 'initio calculated MO Ken effect (MOKE) spectra often provide a minute description of the experimental Ken spectra (see, e.g., Refs. [2-14]). Even the MO KE spectra of lanthanide or actinide com- pounds can be satisfactorily described, provided that the j electrons are sufficiently delocalized [15, 16]. A direct, consequence of the applicability of energy- band theory is that first-principles predictions of MOKE spectra are feasible. Materials can conse- quently, by means of computer calculations, be de- signed and tailored to have special desired MO proper- ties. This aspect is of great technological importance, for example for the search of high-quality MO record- ing materials. Apart from the good MO properties, suitable MO recording materials are required to fulfiIl a number of criteria [17-19]. One of these is a sufficient perpendicular magnetic anisotropy, which sustains the magnetization perpendicular to the optical disk sur- face. Magnetic anisotropies can also be addressed from first-principles, on the basis of relativistic energy-band theory [20-23]' but the theoretical development has not yet progressed equally far. Other requirements, such as, e.g., a Curie temperature suitable for thermomag- netic writing, or temperature-related alloy phase sta- bility, are currently still too complicated to address in a first-principles concept. Concurrent to the progress in technological appli- cations of MOKE, a steady development of fundamen- tal MO research has taken place. The sensitivity of MOKE spectra to the crystalline environment has been exploited to distinguish particular crystal structures 21 [24}. Also, since MOKE results from a lifting of or· bital degeneracy due to spin-orbit int.eraction (SOl) in t.he presence of spontaneous spin polarization, it probes what is essentially the microscopic origin of magnetism. Other fundamental quantities stemming from SOl and spin polarization are the orbital mo· ment and the magnetocrystaHine anisotropy energy (MAE). It is therefore not surprising that the mag· netocrystalline anisotropy reflects itself in the polar MOKE spectra [25-28]. An interesting sequence of re- lationships between these quantities is emerging: The MAE has been related to the anisotropy in the orbital moment [29, 30]. The anisotropy in the orbital mo· ment has in turn been related to the anisotropy in the imaginary part of the off-diagonal conductivity by a new MO sum rule [23]. The latter exemplifies that the off·diagonal conductivity, which is responsible for MO phenomena, is closely connected to the orbital mo- ment. This provides new insight in the origin of MO phenomena. MOKE is to first-order linear in the SOl [3], while the Kerr anisotropy can be a higher order effect [25]. It is usually much smaller than the Kerr ef· feet itself. While it has been demonstrated that MOKE can be reliably calculated from relativistic energy-band theory, its applicability to describe properly the MO Ken anisotropy is an important issue. Recent results indicate that this is indeed the case (7, 24]. However, in order to obtain a complete picture of both the virtues and limitations of the energy-band approach to the MO anisotropy, many more investigations, both theoretical and experimental, have to be carried out. In the fol· lowing such investigations for the XAU4 (X::: V, Cl', Mu) and FeAu and MnAu compounds are reported. 2. The Theoretical Concept The energy-band approach to MOKE spectra has been outlined in detail in several papers [2, 31J. The basic quantity for the evaluation of all optical and MO