Interface Structure and Indirect Coupling in Annealed Fe/Cr/Fe Ultrathin Films

Abstract

Molecular beam epitaxy grown (001) oriented Cr/Fe/Cr and Cr/Fe/Cr/Fe/Cr sandwiches were characterized using the conversion electron Mö ssbauer spectroscopy (CEMS), which proved that the FeCr interface extended up to about 2.5 atomic layers. Analysis of the CEMS results was based on a simple alloy-model of the Fe/Cr interface, resulting in concentration profiles of Fe and Cr atoms. The derived interface model was then used to study the effect of thermal annealing on the film properties. The CEMS studies were correlated with the measurements of the indirect exchange coupling followed by the magneto-optic Kerr effect. Whereas CEMS revealed a measurable effect of annealing on the interface atomic structure for the annealing temperature T A ¼ 200 C, the coupling character began to change at considerably higher temperature (about 400 C).Introduction Among numerous papers concerning coupling in Fe/Cr multilayers, only relatively few deal with Fe/Cr/Fe sandwiches [1-3]. They represent an important tri-layer system of ferromagnetic films coupled through a non-magnetic one, in which the indirect exchange is influenced by different extrinsic factors connected with the spacer and interface atomic and magnetic structure. It has been suggested [3] that the roughness and atomic interface intermixing between Fe and Cr are mainly responsible for suppressing the short-range coupling oscillations, with the period of two Cr(001) atomic layers (AL), and leaving the long-range ones, with the period of 12 Cr AL. Such observations were gathered mainly from studying model systems on single crystalline whisker substrates [3]. Recently, we have undertaken detailed studies of Fe/Cr sandwich structures grown on the commonly used MgO(001) substrates, to find the correlation between the interface structure and the magnetic properties [4]. The conversion electron Mö ssbauer spectroscopy (CEMS) allowed to characterize Fe/Cr interfaces in single Fe films sandwiched between Cr layers on the atomic scale. CEMS offers the unique possibility to locally analyze both the structural and the magnetic properties of buried interfaces. Moreover, the isotopic sensitivity of the method enables depth profiling of iron films using a 57 Fe probe layer embedded during the growth in a film consisting otherwise of 56 Fe. The probe layer concept is here especially useful for verifying an asymmetry suggested for the Fe/Cr and Cr/Fe interfaces [5]. In the present paper we use the derived interface model to follow properties of coupled Fe films in order to find the influence of the annealing induced modification of the interface structure on the type and strength of the coupling.

4H-SiC Power Metal–Oxide–Semiconductor Field Effect Transistors and Schottky Barrier Diodes of 1.7 kV Rating

“…Different hff distributions with larger bulk contributions for Fe on Cr as compared to Cr on Fe interfaces [33] also have a natural explanation within the floating scenario. Further, for thermally annealed Fe/Cr samples our result that the 20 T hff peak is connected with Fe atoms inside Cr layers contradicts the earlier conclusion of other authors [26,51] that long-range (bulk) diffusion takes place exclusively along (and not perpendicular to) the interfaces, leading to interface smoothing.…”

“…The scenario of floating of atoms during the sample growth and the model for calculation of magnetic interface profile can be used for the interpretation of experiments with thin overlayers of Cr/Fe [49] and with Fe films embedded in Cr [50,51]. Kubik et al [50,51] have measured Mössbauer spectra for 57 Fe films of different thicknesses (from 1 to 14 ML) sandwiched between Cr(100) layers.…”

“…Kubik et al [50,51] have measured Mössbauer spectra for 57 Fe films of different thicknesses (from 1 to 14 ML) sandwiched between Cr(100) layers. A discontinuity of magnetic properties at a thickness of 6 ML Fe was observed [50].…”

Electronic and magnetic properties of disordered Fe–Cr alloys using different electronic structure methods

“…Industrial steels with chemical compositions based on an FeCr matrix with Cr concentrations ranging from 2 to 20 at.% are possible candidates for the design of structural components in advanced nuclear energy installations like the Generation IV and fusion reactors [1,2]. Of the various multilayer systems which show oscillatory exchange coupling of ferromagnetic films across non-ferromagnetic spacer layers, Fe/Cr multilayers have shown the greatest promise [3]. It has been felt that, in order to understand multilayers, we must first attempt to understand binary inter-metallic compounds as well as random binary alloys: the former, since in the B2 structure they are naturally occurring models of single atomic multilayers, and the latter, in particular, to give insight into disordering at the multilayer interfaces [4].…”

Structural and Magnetic Properties of Fe50Cr50Alloys Prepared by Mechanical Alloying Method

“…Especially, the Fe-Cr layered magnetic materials were extensively studied for the application of magnetic devices [1][2][3][4][5], and the stainless Fe-Cr alloy has been used in various applications of the structural materials of fuel cells and fusion reactors [6]. The peculiarity of the Fe-Cr system is the existence of a wide miscibility gap in the phase diagram where both Fe and Cr are insoluble at room temperature.…”