JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS Vol. 17, No. 5-6, May – June 2015, p. 686 - 690 Magnetic structure of Fe/Cu(001) thin layers D. BENEA * , S. MICAN, I. STANCIU, A. F. TAKACS, V. POP Faculty of Physics, “Babes-Bolyai” University Cluj-Napoca, Kogalniceanu str. 1 400084 Cluj-Napoca, Romania Ab-initio fully relativistic band structure calculations of Fe films on Cu (001) substrate are presented. The films are modelled as 6Cu/nFe/6Vc slabs, where the number of multilayers (ML) is n=1, 2, 4 and 6. Intermixing between Fe atoms of the thin film and the Cu atoms of the substrate was found to be energetically favourable for 1ML coverage, causing also a decrease of the Fe magnetic moment. The mixing of deposited Fe atoms with the Cu substrate has been studied using the Coherent Potential Approximation (CPA). Various ferromagnetic and ferrimagnetic spin configurations with coupling of layer blocks have been considered, with the in-plane and out-of-plane direction of magnetization. Total energy calculations have been performed and the most stable spin configuration for unrelaxed fcc thin films are shown. While for the 1 and 2 ML Fe/Cu(001) a ferromagnetic out-of-plane spin configuration is the most stable, 4 ML and 6 ML cover regimes exhibit a spin configuration with blocks of layers ferrimagnetically coupled. Layer-resolved spin and orbital magnetic moments in the ground state configuration have also been determined for 1, 2, 4 and 6 ML coverage. (Received July 18, 2014; accepted May 7, 2015) Keywords: Magnetic thin films, Magnetic structure, ab-initio band structure calculations 1. Introduction Thin films and nanostructures show magnetic and electronic properties fundamental different compared with the corresponding bulk materials, allowing a large varia- tion of coercitivity, magnetic anisotropy, magnetic mo- ment and exchange coupling, magnetoresistance and many other properties. In the case of ultra-thin layers, the most important from the magnetic point of view is the dimen- sionality effect, the variation of the magnetic moments at surface and interfaces correlated with the magnetic anisot- ropy arising from low dimensionality due to surfaces and interfaces. Fe films epitaxially grown on a Cu (001) sub- strate is a subject of great interest for more than two dec- ades. Thin films of Fe on Cu (100) show different types of magnetic ordering depending on the layer thickness. Under 4 ML (multilayer) (region I), the thin films show a ferro- magnetic ordering having the Curie temperature higher than room temperature. Between 5 and 11 ML (reg. II), the ferromagnetic order appear just near the surface [1,2]. Alt- hough the image described before is generally accepted, some aspects concerning the magnetic ordering and the spin structure of the Fe/Cu(100) and Fe/Cu(111) films are still unclear. Whilst the ferromagnetic ordering has been established for Fe/Cu(100) in region I [3,4], the physical explanation is still under debate. In the latest studies, the ferromagnetism observed in Fe/Cu(100) films with a thickness under ML is related to the expanding of the atomic volume. The thin films in this region show an en- hanced atomic volume compared with fcc Cu [5], favour- ing the appearance of higher magnetic moments compared with Fe bulk-ones. The magnetic properties of Fe/Cu(100) films in region II can be also be explain using this hypoth- esis. For these films, a fundamental antiferromagnetic state has been accepted by most of the studies [6-8]. Despite of that, the details of the antiferromagnetic configuration of spins and the Néel temperature are still unclear. H.-T. Jeng and D.-S. Wang discovered recently binary alloys of Fe- Co and Fe-Ni with a single layer, deposited on Cu, where a spin reorientation as a function of Fe concentration ap- pears [9]. Concerning the thin films of Fe/Cu(100) in re- gion II, their anomaly magnetic behaviour around 200 K should be mentioned. This behaviour has been observed first by Li et al. [10] in polar MOKE measurements. The magnetization saturation oscillates, with a peak separation of 2.6 ML in region II. A non-collinear spin structure has been excluded in order to explain this behaviour. Similar oscillations have been observed by Qian et al. [11]; they propose a density of spins with antiferromagnetic configu- ration to explain this behaviour. The anomaly magnetic behaviour has been observed also for others bi-layered structures containing layers of bcc Fe in region II (thick- ness between 5 and 11 ML), around 200K [12-14]. San- dratskii studied the fcc Fe/Cu(001) films with 6, 7 and 8 ML coverage and suggested a view on the magnetism of the Fe/Cu(001) films consisting in layers grouped into blocks with collinear magnetic structure [15], the coupling between blocks being ferrimagnetic. Also, it was demon- strated that the variation of the relative direction of the magnetization of different blocks is not relevant. For three surface layers, the magnetic structure has the form  and further layers form pairs with robust ferrimagnetic structure. The formation of an incommensurate SDW in the thin films of Fe/Cu(001), suggested by Qian et al. [11] has been excluded by the studies of Sandratskii [15] and Amemiya et al.[16], proving instead a very strong varia- tion of the magnetization from layer to layer without in- commensurate periodicity. In the present work, we investigate the magnetic or- dering of Fe/Cu(001) films by fully relativistic band struc- ture calculations. We considered Fe/Cu(001) films in fcc structure with the structure 6Cu/nFe/6Vc, where n=1, 2, 4,