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Notes: We have studied the structural properties of Molecular Beam Epitaxy grown thin Co films on α-sapphire (112¯0) substrates by high resolution x-ray scattering measurements in the thickness range of 100 A(ring) to 5000 A(ring). The electron density profile perpendicular to the film plane was determined by x-ray specular reflectivity measurements. The profile contains information about the total metal film thickness, an oxide layer on top of the film and about the surface and interface roughness. The total metal film thickness was compared with the number of coherently scattering atomic planes by taking radial scans through Bragg peaks parallel to the growth direction. Samples up to 400 A(ring) total thickness (out-of-plane mosaicity 0.02(open circle)) show very strong Laue-oscillations about the Co (0002)/(111) Bragg peak. Above a total thickness of 400 A(ring) the oscillations vanish due to a loss in structural coherence. The combination of specular reflectivity and Bragg scans presents a powerful means to analyze the structural coherence of thin films.

Notes: The physics of the growth mechanisms, characterization of epitaxial structures and device properties of GaAs and other compound semiconductors on Si are reviewed in this paper. The nontrivial problems associated with the heteroepitaxial growth schemes and methods that are generally applied in the growth of lattice mismatched and polar on nonpolar material systems are described in detail. The properties of devices fabricated in GaAs and other compound semiconductors grown on Si substrates are discussed in comparison with those grown on GaAs substrates. The advantages of GaAs and other compound semiconductors on Si, namely, the low cost, superior mechanical strength, and thermal conductivity, increased wafer area, and the possibility of monolithic integration of electronic and optical devices are also discussed.

Notes: We present spin polarized neutron reflectivity data on a Co/Cu(111) superlattice and show how not only the magnitude but also the orientation of the average magnetic moment of each layer can be extracted by analyzing the polarization of the reflected beam. This method allows more detailed conclusions about the exchange coupling of magnetic layers across nonmagnetic interlayers and the magnetic in-plane anisotropy in such systems. We present a theoretical fit to the spin-flip and non-spin-flip data which leads to quantitative conclusions about the spin structure. These spin polarized neutron reflectivity results coincide well with the macroscopic magnetic properties which were measured using the magneto-optic Kerr effect revealing a newly discovered uniaxial anisotropy in this system.

Notes: Neutron scattering has been the scattering technique of choice for the analysis of magnetic structures and their dynamics for many decades. The advent of magnetic thin film systems has posed new challenges since such samples have inherently small scattering volumes. By way of examples, recent progress in the application of neutron scattering for the study of both magnetic structure and dynamics in magnetic thin film systems will be presented. First, a combined high angle neutron scattering and polarized neutron reflectivity investigation of the magnetic order of Cr and its influence on the exchange coupling between the Fe layers in Fe/Cr superlattices is discussed. It is shown that in the whole thickness range up to 3000 Å, the magnetic structure is governed by frustration effects at the Fe/Cr interfaces. Second, it is demonstrated that it is now possible to investigate the dynamic properties of magnetic thin films with neutron scattering. Unlike, e.g., Brillouin light scattering, inelastic neutron scattering provides access to large portions of the Brillouin zone. First results on spin wave excitations in a Dy/Y superlattice are presented. © 2000 American Institute of Physics.

Notes: We have examined sputtered metal/Al2O3 multilayers (metal: Co, Pt, W) with respect to their suitability as x-ray mirrors in high temperature environments. The rf-sputtering technique leads to layered structures with interface roughnesses of only 0.2 nm as confirmed by x-ray scattering and transmission electron microscopy. In situ resistance measurements characterize the percolation process and indicate the lower thickness limits for the chosen materials which lead to minimum modulation periods of ≈2 nm. The samples were characterized after stepwise annealing up to 1000 °C. Reflectivity values of nearly 100% at the first satellite-reflection were found in the case of Pt and W (for λ=0.15418 nm). The most stable W/Al2O3 multilayer reflects 70% of the primary beam even after annealing at 900 °C. © 1996 American Institute of Physics.

Notes: We have investigated proximity effects of Fe layers on the spin density waves (SDW) and the concomitant charge density waves or strain waves in thin epitaxial Cr[001] films using synchrotron and neutron scattering. Unlike in bulk Cr we observe a strong anisotropic occupation of the three possible SDWs with their wave vectors Q pointing along the {001} directions. In a pure 3000 Å thick Cr[001] film, the SDW exhibits an almost complete out-of-plane orientation, whereas in a Cr film of the same thickness capped by a 20 Å Fe layer the SDW becomes completely reoriented with Q now propagating in the plane. This SDW is preserved over the entire temperature range from 10 K up to the Néel temperature of about 311 K. © 1997 American Institute of Physics.

Notes: We have prepared by sputtering techniques a series of fcc [Fe1−xNix/Cu]×10 superlattices with sublayer thicknesses of 3 nm and with Ni concentrations x ranging from 0.26 to 0.54. The use of MgO single-crystal substrates and Cu sublayers in the superlattice growth ensures a well-defined fcc crystal structure in the Fe–Ni sublayers with a Ni concentration as low as 26 at. % and down to liquid helium temperatures. The magnetization of the Fe–Ni sublayers in the superlattices starts to deviate from the well-known Slater–Pauling curve at 40 at. % Ni, and continues to drop until the fcc–bcc transition is completed. A strong dependence of the magnetization on temperature was also observed for the Fe–Ni sublayers in the Invar range, consistent with the behavior of bulk Fe–Ni Invar alloys. © 1996 American Institute of Physics.

Notes: Utilizing the magneto-optic Kerr effect (MOKE) in conjunction with x-ray and neutron reflectometry (NR) and diffraction, we have studied the magnetic coupling of Fe/Cr(001) superlattices grown at room temperature and 250 °C. Only the samples grown at elevated temperature exhibit noncollinear coupling of 5.0 nm Fe layers across 1.7 nm Cr interlayers. The noncollinear samples feature a less-disordered in-plane interfacial structure than those grown at room temperature. Using x-ray diffuse reflectivity, we have measured a length scale of 10 nm for these in-plane features. We have also observed, via NR, a remanent noncollinear coupling angle of 50° and, via MOKE and NR, a gradual approach to saturation at upwards of 7 kOe. These features can be explained qualitatively by the proximity magnetism model of Slonczewski. We will compare the predictions of both the proximity and bilinear/biquadratic models with our data and present the results of ongoing neutron measurements of the temperature dependence of the coupling. © 1996 American Institute of Physics.

Notes: We have measured the magnetic anisotropy of high quality Co/Cr(001) superlattices as a function of the Co thickness using the magneto-optical Kerr effect (MOKE) and a torsion magnetometer. The samples grown by molecular beam epitaxy exhibit a reorientational transition of the easy axis from in-plane for large Co thicknesses (tCo≥14 A(ring)) to out-of-plane for 10 A(ring)≤tCo≤14 A(ring) and back again to the in-plane orientation for tCo≤10 A(ring). We provide evidence that this reorientational transition of the magnetization direction is due to a sign change of the interface anisotropy constant induced by a concomitant structural phase transition of the Co layers from hcp to bcc with decreasing Co layer thickness. We have observed antiferromagnetic alignment of the Co layer magnetization both for in-plane and perpendicular magnetic anisotropy. The first maximum of the antiferromagnetic interlayer interaction occurs at tCr=6 A(ring), which is in a good agreement with the results for Fe/Cr(001). In order to theoretically describe the spin structure of the antiferromagnetic coupled multilayers we have performed absolute minima calculations of the angle dependent anisotropy energy. In contrast to trilayer systems we found highly asymmetric spin structures in the superlattices during the remagnetization process. © 1996 American Institute of Physics.

Notes: The interplay between superconductivity (SC) and ferromagnetism (FM) in dilute magnetic alloys and intermetallic compounds attracted considerable attention during the last 30 years. Usually the ferromagnetic state is more stable and therefore tends to suppress SC. On the other hand, the magnetic state can be changed due to a modification of the RKKY interaction in the SC state. Mutual influence of SC and FM may acquire new peculiarities in such artificial systems as FM/SC multilayers. This work is focused on the study of Fe/Nb multilayered system, prepared on Al2O3(112¯0) substrates by rf-sputtering and by molecular beam epitaxy (MBE) techniques. The Nb thickness tNb was varied from 150 to 500 A(ring) and the Fe thickness tFe was changed from 5 to 100 A(ring). The sputtered samples were highly layered with sharp interfaces as revealed by x-ray reflectivity and were textured in the [110] direction. The epitaxial MBE samples showed (110) growth of Nb and Fe with a coherence lengths comprising the total film thickness. Surface and interface roughnesses were very small. The dependence of the ferromagnetic resonance (FMR) spectra parameters on the direction of the dc magnetic field rotating in the plane of the samples show sixfold anisotropic behavior indicating the well known three-domain in-plane structure of Fe layers on sapphire substrates.FMR and SQUID measurements showed that FM of Fe layers survived down to tFe=10 A(ring). The out-of-plane FMR measurements also showed that the easy axis of magnetization lies in the plane of the samples down to this thickness. The superconducting transition temperature Tc was determined by measurements of the electrical resistivity and by SQUID measurements. It was established that there is a critical thickness of the Fe layer tFecrit above which SC was not detected for temperatures down to 1.5 K. This value was dependent on tNb. Thus, for example, it was found that for tNb=300 A(ring) the value of tFecrit=30 A(ring) and for tNb=350 A(ring)—tFecrit=50 A(ring). For constant tFe with increasing tNb up to a certain thickness, SC was not detected; then Tc started to increase, and, finally, it approached the constant value of the order of 6 K above a certain tNb which depended on tFe. The critical magnetic field HC2 obtained from the resistivity measurements, strongly decreased with increasing tFe or decreasing tNb. The temperature dependences of HC2 were typical for two-dimensional superconductors. For the interpretation of the data obtained, various theories were employed. © 1996 American Institute of Physics.