Origin of biquadratic coupling in Fe/Cr(100) superlattices

We investigate the magnetic properties of a (100) oriented [Fe(1.7 nm)/Cr(8.4 nm)](10) superlattice by means of perturbed angular correlation spectroscopy. The magnetic ordering in the Cr layers is obtained by measuring the magnetic hyperfine interaction at implanted 111Cd nuclear probes. We identify dynamic antiferromagnetic spin fluctuations in the Cr layers and show that it gives rise to the biquadratic interlayer coupling.     

Effect of Bi surfactant on the heteroepitaxial growth in Fe/Cr(100) multilayers

This study was to investigate the surfactant effect of Bi on the heteroepitaxial growth of Fe/Cr(100) multilayers by reflection high-energy electron diffraction (RHEED) measurements. With predeposition of submonolayer Bi on Fe(100) prior to evaporation of Fe/Cr multilayer, more long-lasting RHEED intensity oscillations were observed. This implies that the layer-by-layer growth of Fe/Cr multilayer is enhanced. The observations of grazing incidence X-ray reflectivity confirmed that the interface structures of Fe/Cr multilayer with Bi were sharper than that of multilayer without Bi. The study was also to investigate the magnetotransport properties between Bi surfactant-mediated multilayers and normal ones. The magnetoresistance (MR) ratio of the multilayers was enhanced by predeposition of Bi.     

Biquadratic exchange coupling in an unequal Fe/Cr/Fe(1 0 0) trilayer

We have investigated the magnetic properties of a (1 0 0)-oriented unequal trilayer, Fe(45 Å)/Cr(30 Å)/Fe(15 Å), by means of Brillouin light scattering and magnetization measurements. The experimental results show that this sample highlights the effect of biquadratic coupling which aligns the magnetization of the Fe layers at 90° to each other. We extracted the bilinear and biquadratic coupling strengths by fitting the experimental results with a theory that treats the static and dynamic responses on an equal footing. Our results confirm that the model describes both the static and dynamic properties even when the magnetization of the layers is aligned at 90°. The coupling strengths, and their temperature dependence, are discussed and compared with other results reported in the literature.     

Control of interlayer exchange coupling in Fe/Cr/Fe trilayers by ion beam irradiation

The manipulation of the antiferromagnetic interlayer coupling in epitaxial Fe/Cr/Fe(001) trilayers by 5 keV He ion beam irradiation has been investigated. It is shown that even for irradiation with low fluences a drastic change in strength of the coupling appears. For thin Cr spacers (below 0.6-0.7 nm) it decreases with fluence, becoming ferromagnetic for fluences above 2x10(14) ions/cm(2). The effect is connected with the creation of magnetic bridges in the layered system due to atomic exchange events caused by the bombardment. For thicker Cr spacers an enhancement of the antiferromagnetic coupling strength is found. A possible explanation of the enhancement effect is given.     

Initial oxidation stages on FeCr(100) and FeCr(110) surfaces

Simultaneous LEED and AES are used to follow early stages of oxidation of monocrystalline FeCr(100) and (110) between 700 and 900 K in the oxygen pressure range 10^?9–10^?6 Torr. A chromium-rich oxide region at the alloy/oxide interface is observed, which exhibits different surface structures on oxidized FeCr(100) and FeCr(110). The chromium concentration in this initially formed oxide film is found to be enhanced by low oxygen pressures or high temperatures. During further oxidation different behaviours are observed on FeCr(100) and FeCr(110), which are explained by assuming different ion permeabilities through the initial chromium rich oxide regions on the two surface planes. On FeCr(110) surfaces oxidation is initiated on chromium enriched (100) facets at 800 K or below. At 900 K a film consisting of rhombohedral Cr₂O₃ or (Fe, Cr)₂O₃ is epitaxially growing with its (001) plane parallel to the alloy (110) face. On FeCr(100) surfaces the chromium rich oxide region next to the substrate is of fcc type. As soon as the diffusion of iron from the alloy to the gas/oxide interface is observable, a spinel type oxide is formed and connected with the location of iron in tetrahedral lattice sites. Closer to the fcc lattice the spinel oxide consists of FeCr₂O₄ or a solid solution of FeCr₂O₄ and Fe₃O₄ whereas next to the gas phase the oxide is pure Fe₃O₄.     

Search for ferromagnetism in ultrathin epitaxial films: Cr/Au(100), Cr/Cu(100), and Fe/Cu(100)

The surface magneto-optic Kerr effect (SMOKE) technique was used to search for ferromagnetism in monolayer-range films of Cr and Fe grown on Au(100) and Cu(100). The growth modes were characterized using low energy electron diffraction (LEED) and Auger electron spectroscopy. The fcc structure of Cr could not be stabilized on Cu(100). Ferromagnetism was not observed for the Cr/Au(100) films at temperature above 100 K. Ferromagnetism also was not observed for fcc Fe/Cu(100) grown at room temperature; but for growth at >150°C, a ferromagnetic, metastable state was observed for the top layer of the Fe film, in the absence of bulk ferromagnetism. The ferromagnetic Fe/Au(100) system was used to establish the sensitivity of the approach.     

Interlayer magnetic coupling in multilayer magnetic Fe/Cr/Fe systems

The interlayer magnetic coupling of iron layers as a function of the chromium spacer thickness and temperature has been studied for three-layer epitaxial Fe/Cr/Fe films by the methods of Kerr magnetometry and Mandelstam-Brillouin scattering. The results obtained indicate that the short-period component of the interlayer exchange is related to the spin density wave in the chromium spacer.