A combination of STM, SQUID magnetometry, FMR and MOKE is used to study the structural and magnetic properties of thin iron films grown on InAs(001) (4×2)/c(8×2). The different magnetic characterization methods of this paper allow measurements of the magnetic anisotropies in the saturated and non-saturated state. Here we show results of a SQUID/FMR investigation on a 12 monolayer thick Fe film. As expected, FMR measurements find a four-fold symmetry of the magneto crystalline anisotropy, but with an additional uniaxial contribution. The dependence of the remanence on the magnetization angle computed from the magnetic parameters obtained in the saturated state is compared to experimental remanence data measured using MOKE. Good agreement is found. The InAs-substrate quality prior to growth, the nucleation behavior and the thickness-dependent granular structure of the Fe-layer are studied with STM. The origin of the magnetic anisotropies is discussed in terms of these structural data.

We report on magneto-optical Kerr effect (MOKE) measurements of a patterned spin valve system, consisting of few-micrometers-wide Co stripes on a continuous Fe film separated by a 14-nm-thick Cr spacer layer. The spin valve array was studied by regular longitudinal MOKE in specular geometry as well as in Bragg MOKE geometry, using the diffraction spots from the grating for hysteresis measurements. We have investigated the shape of the hysteresis loops and the Kerr amplitude as a function of the diffraction order and for various grating periods. The hysteresis loops measured at the diffracted spots reveal an amplification of the Kerr signal in the field regime where the magnetization of the Fe and Co layers is antiparallel.

The thickness dependence of the helical antiferromagnetic ordering temperature T(N) was studied for thin Ho metal films by resonant magnetic soft x-ray and neutron diffraction. In contrast with the Curie temperature of ferromagnets, T(N) was found to decrease with film thickness d according to [T(N)(infinity)-T(N)(d)]/T(N)(d) proportional variant (d-d(0))(-lambda(')), where lambda(') is a phenomenological exponent and d(0) is of the order of the bulk magnetic period L(b). These observations are reproduced by mean-field calculations that suggest a linear relationship between d(0) and L(b) in long-period antiferromagnets.

We have studied the magnetization reversal of a laterally structured film with both, magneto-optical Kerr effect and with polarized neutron scattering in the off-specular regime. The lateral structure consists of 90-nm thick and 1.2-μm wide Co 0 . 7 Fe 0 . 3 stripes with a grating period of 3 μm. Magnetization reversals were measured for different orientations of the sample with respect to the field directions. In addition, Kerr microscopy was used for visualizing the domain state. Due to the high aspect ratio of the individual stripes, the remagnetization process of the stripe array is dominated by a single domain state over most of the field range. For the casy axis direction, a nucleation and domain wall movement is observed at the coercive field. However, for all other orientations of the stripe array the magnetization reversal is dominated by a coherent magnetization rotation up to the coercive field. For the hard axis orientation the coherent rotation is complete. For this particular stripe array, the agreement between results obtained from MOKE and PNS experiments is very good, mainly due to the specific sample design chosen.

Polarized neutron reflectivity has been used to investigate the peak pattern and the magnetization reversal process of laterally structured Fe- and CoFe-films. The peak pattern of the wire arrays was analyzed in the specular as well as in the off-specular regime. The intensities of the different cross-sections at the off-specular first-order peak were investigated as a function of external magnetic field. Magnetization reversals are discussed and compared to MOKE studies of the same system.

We used the magneto-optical Kerr effect (MOKE) in longitudinal configuration to study the reversal mechanism of ferromagnetic gratings patterned by electron beam lithography. In addition to the conventional specular configuration, we utilize the MOKE also in off-specular geometry for the investigation of magnetization loops at different orders of diffraction n. The nth order of diffraction is particularly sensitive to the nth-order Fourier component of the magnetization distribution. Accordingly, the shape of the hysteresis loops changes characteristically as a function of n, indicating an enhanced sensitivity for the formation of magnetic domains close to remanence.

We have carried out detailed experimental studies of the exchange bias effect of a series of CoO/Co(111) textured bilayers with different Co layer thickness, using the magneto-optical Kerr effect, superconducting quantum interference device (SQUID) magnetometry, polarized neutron reflectivity, x-ray diffraction, and atomic force microscopy. All samples exhibit a pronounced asymmetry of the magnetic hysteresis at the first magnetization reversal as compared to the second reversal. Polarized neutron reflectivity measurements show that the first reversal occurs via nucleation and domain wall motion, while the second reversal is characterized by magnetization rotation. Off-specular diffuse spin-flip scattering indicates the existence of interfacial magnetic domains. All samples feature a small positive exchange bias just below the blocking temperature, followed by a dominating negative exchange bias field with decreasing temperature.

In this article, we observed strong dipolar coupling between magnetic strips influencing the resulting magnetisation patterns. The resulting domain structures depend not only on the magnetic anisotropy, but also strongly on the magnetic history of the samples.

Sputtered polycrystalline iron gratings with a varying stripe width between 0.5 and 3.7 /spl mu/m at a constant periodicity of 5 /spl mu/m were studied by Kerr microscopy. The magnetic anisotropy direction is aligned transverse to the stripe length axis. The observed domain processes are directly compared with hysteresis curve measurements. Domain nucleation and the resulting domain structure depend on the external magnetic field direction. Complicated multidomain states are observed down to a stripe width of 1.7 /spl mu/m. The most narrowly spaced stripes display a simple domain configuration with the average magnetization vector perpendicular to the stripes, along the full film anisotropy axis, indicating dipolar coupling between the elements. With decreasing stripe width and increasing stripe distance, a change to a Landau-Lifshitz-like domain pattern is found. For very narrow stripes, it transforms into a ripple modulated domain structure. Altogether, a continuous transition from full-film-like to single strip-like magnetization behavior with increasing stripe spacing is found. The results are explained by the existing uniaxial magnetic anisotropy together with the shape anisotropy increasing with reduced stripe width. The strong influence of coercivity on the magnetization patterns is shown.

An optimized heterostructure design and an optimized surface sputter-cleaning procedure allow the growth of high-quality epitaxial Fe(001) thin films at Ts<∼50 °C on selectively doped GaAs/Al0.35Ga0.65As heterostructures, while retaining the high quality transport property of the two-dimensional electron gas. Magneto-optic Kerr effect measurements and model calculations indicate a dominant uniaxial in-plane anisotropy (easy axis along [110], hard axis along [1−10]) and small coercivity (∼15 Oe). Interface sensitive Fe57 Mössbauer measurements prove the absence of both magnetic “dead layers” and “half-magnetization” phases (compared to pure Fe), and provide evidence for intermixing within a few monolayers, retaining, however, a metallic Fe state and high Fe magnetic moments at the interface.

Fe(0 0 1) thin films (70 Å) with 57Fe(7.2 Å) tracer layers at the interface were epitaxially grown on GaAs(4×6) surfaces. Magneto-optic Kerr effect and Ferromagnetic resonance measurements indicate a dominant 2-fold in-plane magnetic anisotropy (easy axis along [1 1 0]) superimposed to a 4-fold anisotropy, and small coercivity (∼10 Oe). Mössbauer (CEMS) measurements indicate no magnetic “dead layer” and an average Fe moment of ∼1.7–2 μB at the Fe/GaAs interface.

The magnetooptical Kerr effect in longitudinal configuration is used to measure hysteresis loops of ferromagnetic Fe-gratings grown on Al2O3 at different orders of diffraction. At even order of diffraction the hysteresis loops exhibit anomalies which can be attributed to the interference of the magnetic and non-magnetic parts of the grating. The Kerr angle in saturation increases linearly with the order of diffraction.

We study magnetic hysteresis loops after field cooling of a CoO/Co bilayer by MOKE and polarized neutron reflectivity. The neutron scattering reveals that the first magnetization reversal after field cooling is dominated by domain wall movement, whereas all subsequent reversals proceed essentially by rotation of the magnetization. In addition, off-specular diffuse scattering indicates that the first magnetization reversal induces an irreversible change of the domain state in the antiferromagnet.

The structural properties of epitaxial L1(0) ordered FePt(001) films, grown by molecular beam epitaxy, (alternating deposition of Fe and Pt atomic layers) on buffer-Pt/seed-Fe/GaAs(001) have been studied by in situ reflection high-energy electron diffraction and by ex situ x-ray scattering as a function of the growth conditions. Reflection high-energy electron diffraction intensity oscillations measured during FePt layer growth provide evidence for island growth at T-s = 200 degreesC and quasi layer-by-layer growth at T-s = 350 degreesC. From small-angle and wide-angle x-ray scattering it was found that the degree of epitaxy depends critically on morphology of the seed layer and the substrate roughness. X-ray diffraction analysis showed that the long-range order parameter increases from near zero for films grown at 200 degreesC to 0.65 for films grown at 350 degreesC. This confirms the fact that the order parameter is mainly determined by the surface mobility of the atoms which is controlled experimentally by the substrate temperature.

We have investigated via SQUID magnetometry and polarised neutron reflectivity the exchange-bias effect in CoO/Co sputtered multilayers. In particular, we studied the magnetisation reversal and the time relaxation of the exchange-bias field close to the coercive field Hc1. Neutron intensities of all four cross sections (I++, I+-, I-+, I–) were recorded at the position of the first multilayer Bragg peak while scanning the magnetic field. From such scans we infer that the magnetisation reversal for the ascending as well as for the descending branch of the magnetic hysteresis occurs not by in-plane rotation but through domain-wall movements. The exchange-bias field, HEB, is strongly affected by thermal fluctuations. HEB decreases, following an exponential decay function with a half-life time of about 580 s at T=240 K.

We discuss results of magneto-optical Kerr effect (MOKE) measurements performed on a thin Fe film of 13 nm thickness, which has been patterned into a periodic arrangement of nanowires by means of optical interference lithography. The resulting array of nanowires consist of stripes having a width of 150 nm and a periodicity of 300 nm. MOKE hysteresis loops are measured within magnetic fields which are aligned in different directions, both parallel and perpendicular with respect to the direction of the nanowires as well as for various angles in between. A particular arrangement of the longitudinal Kerr effect measurement allows us to identify both the longitudinal and the transverse component of the magnetization of Fe nanowires. From this both the angle and the magnitude of the magnetization vector are derived. For a non-parallel alignment of the nanowires with respect to the direction of the external magnetic field, the hysteresis loops consist of a plateau region with two coercive fields Hc1 and Hc2, which is discussed as resulting from an anisotropic pinning behaviour of magnetic domains in directions along and perpendicular to the nanowires.

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.

We report measurements of the magneto-optical Kerr effect (MOKE) on an optical grating of Ni-stripes on Si(111) and a grating of Al-stripes on a Ni thin film. The analysis of the MOKE signal at different orders of diffraction n reveals a change of the Kerr signal amplitude, which is periodic in n having the same periodicity as the total intensity of the diffracted light. For the grating of Ni-stripes we observe a definite change of the shape of the magnetic hysteresis loops also varying systematically with the order of diffraction n.

Using temperature-dependent measurements of the magneto-optical Kerr effect (MOKE) we map out a magnetic phase diagram of Fe/Cr(001) superlattices with Cr-thicknesses between 10 to 45 Å in a temperature range from 10 to 700 K. By comparison with neutron scattering results, we demonstrate the strong correlation between different magnetic phases of the Cr interlayers and the coupling between the Fe layers. We find an enhancement of the Cr Neél temperature as we reduce the Cr thicknesses, indicating a strong proximity effect between the Fe and Cr layers.

We present the results of temperature dependent measurements of magnetically coupled Fe1−xCrx/Cr-superlattices. These results are supplementary to the ones known for non-collinearly coupled Fe/Cr-superlattices. By systematically varying the Cr concentration x we cover a wide range of the Fe1−xCrx-phase diagram. As an experimental technique spin-polarized neutron reflectivity with spin analysis and high-angle neutron scattering proves to be ideal for this work.