Eur. Phys. J. B 16, 653–658 (2000) T HE EUROPEAN P HYSICAL JOURNAL B c  EDP Sciences Societ` a Italiana di Fisica Springer-Verlag 2000 Magnetic properties of (Co n Pd m ) r superstructures on Pd(100) and Pd(111) U. Pustogowa 1 , C. Blaas 1 , C. Uiberacker 1 , J. Zabloudil 1 , P. Weinberger 1 , L. Szunyogh 2, 1 , and C. Sommers 3, a 1 Center for Computational Materials Science, Gumpendorfer Str. 1a, 1060 Vienna, Austria 2 Department of Theoretical Physics, Technical University Budapest, Budafoki ´ ut 8, 1521, Budapest, Hungary 3 Laboratoire de Physique des Solides, Universit´ e Paris-Sud, 91405 Orsay Cedex, France Received 3 November 1999 and Received in final form 18 January 2000 Abstract. The magnetic properties of (ConPdm)r superstructures on Pd(100) and Pd(111) are evaluated using the fully-relativistic spin-polarized screened Korringa-Kohn-Rostoker method. It is found that only in the case of a Pd(111) substrate such superstructures exhibit perpendicular magnetism, while on a Pd(100) substrate the magnetization is oriented in-plane. Also investigated is the effect of interdiffusion in repeated superstructures. By using the inhomogeneous coherent potential approximation (CPA) for layered systems the effect of ordering into (repeated) superstructures can be described in an ab-initio-like manner. It is found that already small amounts of interdiffusion can be decisive for the actual value of the magnetic anisotropy energy. PACS. 75.70.Cn Interfacial magnetic properties (multilayers, magnetic quantum wells, superlattices, magnetic heterostructures) – 71. Electronic structure 1 Introduction Co/Pd superstructures on suitable substrates raised con- siderable interest because of possible applications for magneto-optical storage media. In quite a few experimen- tal papers [1–6] various aspects of perpendicular mag- netism in these systems were discussed, in particular the exceptionally strong dependence on the (surface) orienta- tion of the substrate. In the theoretical papers on this topic [7–11] not only magneto-optical properties of or- dered and disordered bulk systems [7,8] were calculated using different theoretical and computational schemes, but also in a preliminary manner the question of the magnetic anisotropy and its microscopic sources was addressed. The aim of this paper is to present a theoretical study of the magnetic properties of (Co n Pd m ) r superstructures on Pd by varying the sequence of Co and Pd layers, i.e., by varying n and m and the number of repetitions r, and to discuss the effect of the growth direction, i.e., the effect of the surface orientation of Pd serving as substrate. In addition to the ordered superstructures, interdiffusion at the Co/Pd interfaces will be discussed for exactly that system which, when ordered completely, has the highest perpendicular magnetic anisotropy energy per repetition. a e-mail: sommers@lps.u-psud.fr 2 Computational aspects All calculations were performed using the fully-relativistic spin-polarized screened Korringa-Kohn-Rostoker method [12–14]. In all cases the effective potentials and effective exchange fields were obtained self-consistently based on the exchange-correlation functional given in reference [15], by making use of surface Brillouin zone integrations with 45 k ‖ vectors per irreducible wedge (ISBZ), and a “buffer” of three Pd layers to the semi-infinite Pd sub- strate. The band energy differences ∆E b between a uni- form perpendicular-to-plane and a uniform in-plane orien- tation of the magnetization was then evaluated in terms of the magnetic force theorem (see also Ref. [16]) using 990 k ‖ vectors per ISBZ (for further computational de- tails see Refs. [17–19]), guaranteeing well-converged quan- tities. For describing interdiffusion the CPA for layered systems [20] was applied using the same numerical pa- rameters just mentioned. All calculations refer to the experimental lattice spac- ing (a 0 = 7.3530 a.u.) of a Pd fcc “parent lattice” [21], i.e., no layer relaxations were considered although in principle this would be possible [18]. It should be noted that in the case of a Pd(100) substrate the (constant) interlayer spacing (3.6765 a.u.) is substantially shorter than for a Pd(111) substrate (4.2454 a.u.). As is well-known, the magnetic anisotropy energy ∆E a consists of two contributions, the band energy term