Solid State Phenomena Vols. 152-153

Abstract: The technique of finite difference equations is used for an analytical investigation of field-induced transitions in magnetic multilayers. Heisenberg and biquadratic exchange interactions and uniaxial anisotropy are taken into account. The analytical dependencies of critical field values determining the stability of ferromagnetic and antiferromagnetic phases on the layers number are obtained.

Abstract: The goal of this work is to justify a possibility to obtain and observe coherent spin relaxation—the superradiation (SR) effect—in molecular nanomagnetic structures. We note that giant-spin molecules have the magnetic moments of the order of and possess substantial magnetic anisotropy. Moreover, to invoke SR, such a system should be polarized to a high extent. When put together, these factors rule out the conventional treatment used e.g. for optical SR, and invoke development of novel approaches.

Abstract: Results on the investigation of magnetic and magneto-optical properties of nanocrystalline Fe/Zr and Fe/Zr, Mo/Fe thin-film systems are presented. The examined samples were prepared by DC magnetron sputtering technique. The structural investigations of the samples were performed by X-ray diffraction analysis. The hysteresis loops and spectral dependencies of the transverse Kerr effect were measured employing the magneto-optical magnetometer and the magneto-optical spectrometer, respectively. The influence of the Zr and Mo layer thickness on the magnetic and magneto-optical properties of the examined samples was observed.

Abstract: The quantum Heisenberg antiferromagnet on the stacked triangular lattice with the intralayer nearest-neighbor exchange interaction J and interlayer exchange J' is considered within the non-linear -model with the use of the renormalization group (RG) approach. For J'  J the asymptotic formula for the Neel temperature TNeel and sublattice magnetization are obtained. RG turns out to be insufficient to describe experimental data since it does not take into account the 2-vortices. Therefore TNeel is estimated using the Monte-Carlo result for the 2D correlation length [10] which has a Kosterlitz-type behavior near the temperature TKT where the vortices are activated.

Abstract: We report the first direct experimental evidence of the presence of antiferromagnetic dimers in VOx nanotubes based on the high frequency (60 GHz) electron spin resonance study carried out in the temperature range of 4.2-200 K. Arguments favouring a possible observation of the low temperature quantum critical phenomena in VOx nanotubes are provided.

Abstract: In this report the results on the investigation of magnetic states of Fe and Co ions in superlattice [Mo(12Å)Co(21Å)Fe(14Å)]*100 are presented. The magnetic superlattices were obtained by means of cathode sputtering in discharge with oscillating electrons. The results of X-ray diffraction show that magnetic superlattices (MSL) have amorphous state. The magnetic states of Fe and Co ions were investigated using Mössbauer spectroscopy (MS) and electron spin resonance (ESR) for the as-deposited MSL and after annealing at 450°C. The results of our studies of Fe and Co ions states indicate that they correspond to high-spin states in clusters Fen, Com, FenCom, FenMom with small number of atoms n, m in clusters.

Abstract: The comparative study of Fe2O3 4-10nm nanoparticles incorporated in arabinogalactan and polyvinyl alcohol matrixes was performed by means of magnetic measurements in wide 5-900K temperature range, Mossbauer spectroscopy and transmission electron microscopy. The processes of nanoparticles different self-organization inside various polymer matrixes were revealed. These processes lead to unusual magnetic behavior of initially superparamagnetic nanoparticles owing to interparticle interactions.

Abstract: Highly ordered arrays of Fe antidot films were fabricated by thermal vapor deposition technique using nanoporous alumina templates. The film thickness varies from 20 up to 100 nm, and the antidots array has about 50 nm in diameter and 105 nm of periodic interspacing. Scanning electron microscopy and atomic force microscopy measurements confirmed that the Fe antidots film retains the well-ordered hexagonal structure of the nanoporous alumina template. Meanwhile, the micromagnetic structure was studied by magnetic force microscopy and SQUID measurements. A stripe magnetic domain pattern featuring a large out-of-plane magnetization component is found in the films. Noteworthily, the magnetic domains are not pinned by the nanopores but, on the contrary, several antidots are included in each magnetic domain. According to the magnetic measurements, the easy magnetization axis of the Fe antidot array remains in the film plane, while the hard one lies perpendicular to the plane, which can be explained on the basis of the different contributions of the nanoholes to the total magnetic anisotropy of the antidots film.

Abstract: Results obtained during examination of the multilayer Co/Au film by different methods of Magnetic Force Microscopy (MFM) are presented. It was shown, that double-pass scanning with MFM tips, characterised by strong magnetic moments resulted in a magnetisation reversal of the sample during MFM imaging. Single pass scanning or use of the MFM tips with low magnetic moments was required to minimise this process. Experimental results demonstrated good correlation between MFM results acquired during single-pass scanning and double-pass scanning with MFM tips characterised by low magnetic moment.

Abstract: We have investigated the thermodynamic, transport and magnetotransport properties of free charge carriers in a diluted magnetic semiconductor with a quantum well InGaAs in the GaAs with δ-doped by C and Mn. In order to determine the density of the holes in a quantum well, we carried out thermodynamic calculations of the system of free holes, atoms Mn0 and ions Mn–. We calculated the temperature dependence of resistance and magnetoresistance of holes in the quantum well. The contributions of various scattering mechanisms of holes to the resistance were analyzed. The negative magnetoresistance are explained as the reduction of spin-flip scattering by aligning spins of the magnetic field.