[en] We present a novel high-T_C-SQUID magnetometry for absolute determination of the total magnetic moments in UHV. Co/Cu (0 0 1) films 2-17 monolayers (ML) thick are studied with submonolayer sensitivity at temperatures from 65 to 300 K. By combination with the findings of the X-ray magnetic circular dichroism for the ratio of spin μ_S to orbital μ_L magnetic moment, both contributions are determined. The outcome is a spin magnetic moment that is almost constant, while the orbital moment increases from 17 to 2 ML by a factor of 2

[en] We have investigated epitaxial MnAs/GaAs(0 0 1) films in the phase transition region between 10 deg. C and 40 deg. C where hexagonal, ferromagnetic α-MnAs and paramagnetic, orthorhomic β-MnAs coexist. Quantitative stress measurements with a cantilever beam magnetometer reveal that during the phase transition the atomic distances change only in the vertical direction providing insight into the nature of the exchange coupling mechanism

[en] The superconducting quantum interference device (SQUID) magnetometer is one of the most sensitive experimental techniques to magnetically characterize samples with high sensitivity. In cases where thin films on substrates are studied great care has to be exercised to subtract the diamagnetic response of the substrate, in particular, if the magnetization is measured in different orientations. Here it will be shown that the assumption of an isotropic, temperature-independent diamagnetism is only a first approximation. One has to consider anisotropic contributions to the diamagnetism in anisotropic crystals such as sapphire as well as temperature-dependent van Vleck-like components in semiconductor substrates such as GaAs or Si. When great care is exercised it becomes feasible to measure, for example, the anisotropic paramagnetic properties of thin films of dilute magnetic semiconductors (DMS) using SQUID. This will be illustrated by measurements of the DMS Co-doped ZnO

[en] Temperature-dependent studies are performed in situ on Ni/Cu(0 0 1) and Co/Cu(0 0 1) ultrathin films by AC-susceptibility and the element-specific X-ray magnetic circular dichroism. It is shown that the growth of a Cu capping layer reduces considerably the Curie temperature by about 30-40 K for Ni and 100 K for Co films. The effect is practically completed after the growth of the first few monolayers of the Cu capping layer. Further growth of Cu does not alter significantly the Curie temperature. We show that the Cu-capping results in a decrease of the magnetic moments and the relation of it to the reduced Curie temperatures is discussed

[en] Thin films of MnAs grown on GaAs(0 0 1) show a self-organized structure of coexisting ferromagnetic α- and paramagnetic β-MnAs stripes in the temperature interval from 10 to 40 deg. C. We quantify the magnetic anisotropies of the α-stripes via ferromagnetic resonance and superconducting quantum interference device magnetometry for samples with thicknesses of 57 and 165 nm. The easy axis of magnetization is found to be located perpendicular to the stripe direction, whereas the direction parallel to the stripes is a hard one. While the intrinsic anisotropies show a bulk-like behavior and explain the direction of the hard axis, the key to understanding the direction of the easy axis is given by the demagnetizing fields due to the stripe formation

[en] Bilateral synchronous involvement of the orbits by lymphoma is an uncommon event. Therefore, the irradiation techniques for this disease are not well refined. Depending on the technique used, one has to decide between underdosing the anterior segment of the orbit and the frequency involved lacrimal glands or to tolerate shield related inhomogeneities in the range of 40 to 50% as well as higher doses to the midline structures, e.g. the optic chiasma. To avoid the above shortcomings the authors developed a technique by which half the prescribed dose is delivered by pairs of beams angulated in the transverse plane and the other half by pairs of beams angulated in the sagittal plane. Film dosimetry in a phantom confirms that the entire orbit, including its anterior portion, is well covered, the lens is protected, and the dose to the mid-sagittal structures is not increased. The dose inhomogeneity is in the range of 20% which presents a substantial improvement over alternative methods. Two irradiated patients with bilateral orbital lymphoma are presented with local control and no ophthalmic or other side effects as of last follow-up. (Auth.)

[en] Photometric observations of the nova V404Cyg have been performed during 1989 May - July, immediately following its recent outburst. Measurements in the R photometric band have revealed periodic variability superposed on the general decline in the brightness of the star by 3 mag during that interval. The amplitude of the cyclic variation decreased from 0.24 mag in May - June, to 0.06 mag in July. A period analysis of the data suggests that the photometric cycle has a period of 3.0455 hr. This may well be the orbital period of the V404Cyg binary system. (Author)

[en] The superconducting quantum interference device (SQUID) magnetometer is one of the most sensitive experimental techniques to magnetically characterize samples with high sensitivity. Here we present a detailed discussion of possible artifacts and pitfalls characteristic for commercial SQUID magnetometers. This includes intrinsic artifacts which stem from the inherent design of the magnetometer as well as potential issues due to the user. We provide some guidelines on how to avoid and correct these, which is of particular importance when the proper magnetization of nanoscale objects will be established in cases where its response is dwarfed by that of the substrate it comes with, a situation frequently found in the field of nanomagnetism

[en] A series of high quality Zn_1-xCo_xO films prepared by reactive magnetron sputtering displays altered magnetic properties ranging from paramagnetic (PM) to ferromagnetic (FM)-like at room temperature. With tuning the properties of the Zn_1-xCo_xO films from PM- to FM-like, the temperature dependent resistivity of the films changes from a Mott variable-range hopping to an Efros variable-range hopping process. This indicates the emergence of a Coulomb gap, which can be explained by the presence of nanoclusters. Moreover, the anhysteretic M (H)-curves above the blocking temperature for superparamagnetic (SPM) films can be described by a Langevin function, which confirms the existence of FM nanoclusters. The investigation on the magneto-transport of these films shows no spin-dependent transport behaviour associated with the observed FM-like/SPM properties.

[en] The use of synchrotron-based spectroscopy has revolutionized the way we look at matter. X-ray absorption spectroscopy (XAS) using linear and circular polarized light offers a powerful toolbox of element-specific structural, electronic, and magnetic probes that is especially well suited for complex materials containing several elements. We use the specific example of Zn_1-xCo_xO (Co:ZnO) to demonstrate the usefulness of combining these XAS techniques to unravel its intrinsic properties. We are able to demonstrate, that as long as phase separation or excessive defect formation is absent Co:ZnO is paramagnetic and we can establish independent quality indicators based on XAS. Samples which show long-range magnetic order fail to meet the quality indicators and complementary experimental techniques such as x-ray diffraction and transmission electron microscopy indeed prove phase separation. By deconvoluting the XAS spectra, the characteristic spectral features of the phase separated materials are derived.