Origin of the polar Kerr rotation in ordered and disordered FePt multilayers M. Kharoubi a,b , A. Haroun c , M. Alouani a,⇑ a Institut de Physique et Chimie des Matérieux de Strasbourg, CNRS-UdS, UMR 7504, 23 rue du Loess, BP 43, 67034 Strasbourg Cedex 2, France b Laboratoire d’opto-électronique et composants, Département de physique, Université Ferhat Abbas-Cité Maâbouda, 19000 Sétif, Algeria c Laboratoire de physique quantique et des systèmes dynamiques, Département de physique, Université Ferhat Abbas-Cité, Maâbouda, 19000 Sétif, Algeria article info Article history: Received 8 November 2012 Received in revised form 10 January 2013 Accepted 12 February 2013 Available online 16 March 2013 Keywords: Ab initio electronic structure Magneto-optical Kerr effect Optical conductivity abstract The electronic structure and the magneto-optical properties of ordered and disordered FePt multilayers have been calculated by means of the spin-polarized relativistic linear muffin-tin orbital (SPR-LMTO) method within both the local spin-density approximation (LSDA) and generalized gradient approxima- tion (GGA). Both approximations lead to the same magneto-optical results. The ordered FePt magneto- optical properties have also been calculated within the linear augmented plane wave method and the results are in good agreement with the SPR-LMTO calculations. The complex Kerr angle for ordered and disordered FePt has been calculated for photon energies of up to 6 eV and is found to be in a good agreement with experiment. Different structures in the optical conductivity and Kerr rotation as a func- tion of the photon energy are analyzed and discussed. To show the microscopic origin of the strong Kerr rotation at some particular photon energies the symmetry character of the bands contributing to inter- band transitions together with with the interband electric dipole momentum matrix elements are ana- lyzed in the whole Brillouin zone (BZ). This analysis showed that the assignment of the peaks is complex and cannot only be attributed to interband transitions along high symmetry BZ directions. Ó 2013 Elsevier B.V. All rights reserved. 1. Introduction The magneto-optical Kerr effect (MOKE), which is due to the interplay of spin-polarization and spin–orbit coupling, is one of the most used standard techniques for studying the magnetic properties of materials and magnetic recording. This effect occurs when a magnetic material reflects light; a linearly polarized light becomes elliptically polarized and the plane of Polarization rotates. Typically this effect is not very large for the 3d materials but it yields important information about their magnetic properties as it is sensitive to the local magnetic environment of the 3d atoms. From the industrial point of view, there is always a growing need for high storage devices for the information technology. The suc- cess with the magneto-optical hard disks opens a new area of re- search for the optimization of the recording devices based on multi layered materials and optical probing. Enhancing the MOKE in materials has become a major focus of research with a direct implication of improving recording media. In this respect, half me- tal [1] magneto-optical properties have been studied by many authors [2–7], but their interpretation is difficult due to the inter- play between orbital, spin, charge and structural degrees of free- dom. Perovskite magnates, such as La x Sr 1x MnO 3 have been also studied [8]. The MOKE spectra of dilute magnetic semiconductors, such as Ga 1x Mn x As, have been also investigated [9], but here again their interpretation is difficult due to the presence of interstitial and substitutional Mn. On the other hand, multilayers are the materials of choice for studying MOKE because of the oscillations of the exchange coupling as a function of the spacer thickness, which results in the oscillation of the Kerr rotation. In addition, multilayers offer more advantages over transition metal alloys be- cause they are generally more stable, less corrosive. Magnetic materials that are resistant to oxidation can therefor be selected to avoid loss of the MOKE signal. Although the theoretical origin of the MOKE has been known by Argyres in the mid-fifties [10], a quantitative agreement with experiment has been obtained only in the beginning of the nineties [11–17] due to the difficulties in computing accurately the dielec- tric tensor when both the spin polarization and the spin–orbit cou- pling are included in the calculation. It is only most recently that effects of electronic correlation, within the so called dynamical mean-field theory, on the magneto-optical spectra of NiMnSb have been computed [5], and resulted in a noticeable improved agree- ment with corresponding experimental results. The pseudopoten- tial method has also been shown to produce accurate MOKE spectra of Fe, Co and Ni, however, starting from the density–density correlation function, neglecting the term which describes the anomalous hall effect, produced a wrong optical conductivity 0927-0256/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.commatsci.2013.02.012 ⇑ Corresponding author. Tel.: +33 3 88 10 70 06; fax: +33 13 88 10 72 49. E-mail address: mea@ipcms.unistra.fr (M. Alouani). Computational Materials Science 73 (2013) 24–32 Contents lists available at SciVerse ScienceDirect Computational Materials Science journal homepage: www.elsevier.com/locate/commatsci