Magnetic structure of thin films of Fe x Mn 1 Àx on Cu„100…ÕCo by the fully relativistic screened KKR method L. Szunyogh Center for Computational Materials Science, Technische Universita¨t Wien, Getreidemarkt 9/134, 1060 Vienna, Austria and Department of Theoretical Physics, Budapest University of Technology and Economics, Budafoki u´t. 8, Budapest 1521, Hungary J. Zabloudil Center for Computational Materials Science, Technical University of Vienna, Getreidemarkt 9/134, Vienna A-1060, Austria P. Weinberger Center for Computational Materials Science, Technical University of Vienna, Getreidemarkt 9/134, Vienna A-1060, Austria F. Offi Max-Planck-Institut fu¨r Mikrostrukturphysik, Weinberg 2, Halle/Saale D-06120, Germany W. Kuch Max-Planck-Institut fu¨r Mikrostrukturphysik, Weinberg 2, Halle/Saale D-06120, Germany J. Kirschner Max-Planck-Institut fu¨r Mikrostrukturphysik, Weinberg 2, Halle/Saale D-06120, Germany ~Received 8 August 2002; published 28 February 2003! The fully relativistic screened Korringa-Kohn-Rostoker method is used to discuss the electronic structure and magnetic properties of Fe x Mn 12x overlayers on Cu~100!/Co. It is found that in this system, energetically low-lying antiferromagnetic configurations most likely are the cause for the experimentally observed antifer- romagnetism. In all cases investigated, the ground state corresponds to the ~in-plane! ferromagnetic configu- ration; the Fe x Mn 12x overlayers do carry a small ~concentration averaged! magnetic moment. In very good agreement with experiment, two overlayer thicknesses, namely, at 3 and 10 ML, are traced, at which either this moment nearly vanishes ~3 ML! or different types of antiferromagnetic configurations apply ~10 ML!. DOI: 10.1103/PhysRevB.67.054418 PACS number~s!: 75.30.Gw, 75.70.Ak, 75.70.Cn I. INTRODUCTION Antiferromagnetic/ferromagnetic heterostructures turned out in the past to be of considerable interest because of possible applications in spin valve systems. Since in the bulk phase, fcc Fe 50 Mn 50 is antiferromagnetic and of nearly the same lattice spacing as fcc Cu, with a rather small misfit as far as the interlayer distance is concerned, for Co over- layers on Cu~100!, a combination of these three ingredients ~Cu, Co, and Fe 50 Mn 50 ) in one system seems to be ideally suited for the search of new properties. As usual, once these partial systems are combined in a multilayer system, vir- tually none of the characteristic bulk features seems to apply. Recent experimental investigations 1–4 of the system Cu(100)/Co/Fe 50 Mn 50 revealed rather puzzling results: on the one hand typical features of antiferromagnetism, such as critical temperatures at which antiferromagnetism disap- pears, were found. At 10 ML Fe 50 Mn 50 thickness, this critical temperature equals room temperature. On the other hand, ferromagnetic moments of Fe and Mn were also traced. It is therefore quite tempting to discuss these findings using an ab initio approach. In the present paper, first the theoretical and computa- tional details are briefly summarized, followed by a presen- tation of the results. In the following section, the main as- pects of the experimental investigations are then reviewed and related to the theoretical results. The conclusion once again stresses the importance of the investigated system and the close relationship between theory and experiment. II. THEORETICALAND COMPUTATIONAL DETAILS The fully relativistic spin-polarized screened Korringa- Kohn-Rostoker method for layered systems 5 is applied within the framework of the coherent-potential approxima- tion 6 in order to calculate the electronic structure and mag- netic properties of Fe x Mn 1 2x overlayers on Cu(100)/Co 6 . In all calculations, an fcc parent lattice 7 is assumed with a lat- tice spacing a 0 of 6.8309 a.u. ~bulk fcc Cu!, i.e., no layer relaxation is considered, and six Cu layers serve as buffer to the semi-infinite Cu substrate. In order to determine self- consistently within the local-density approximation 8 the ef- fective potentials and effective exchange fields, a minimum of 45 k i points in the irreducible wedge of the surface bril- louin zone ~ISBZ! is used. All self-consistent calculations refer to a ferromagnetic ~parallel! configuration C 0 with the orientation of the magnetization pointing along the surface normal. In the present study, only collinear magnetic con- figurations are considered. Let D E ( C i ) denote 5 the energy difference of a particular magnetic configuration C i with respect to the reference con- figuration C 0 , PHYSICAL REVIEW B 67, 054418 ~2003! 0163-1829/2003/67~5!/054418~9!/$20.00 ©2003 The American Physical Society 67 054418-1