Solid State Phenomena Vols. 233-234

Abstract: This work reports study of magnetic properties of the ε-In_0.24Fe_1.76O₃ nanowires possessing 6 kOe coercive force at room temperature. Freezing of the sample below 190 K causes sharp decrease of the coercive force and magnetization of nanowires driven by the easy axis spin-flop transition.

Abstract: The total energy, geometry and electronic spectra of nanoclusters \shm{} ($m=0\ldots11$) are calculated using the evolutionary algorithm and density functional theory (DFT). It is shown, that the features of electron spectrum, namely HOMO-LUMO gap and valence band width, correlate with cluster geometry and stability. The HOMO-LUMO gap becomes wider as the number of hydrogen atoms increases whereas the width of valence band gets lower. The widening of the band gap indicates the increasing of cluster stability which is consistent with existing data on reaction energy.

Abstract: Multilayer nanogranular film structures (CoFeB)_m(SiO₂)_100-m have been investigated by ferromagnetic resonance (FMR). It is shown experimentally that for these films which magnetic phase content is below percolation threshold the variation of FMR fields is not related to the thickness of magnetic layers but can be explained by variation of the shape (elongation) of spheroidal magnetic granules. The observed results are explained within standard phenomenological FMR theory.

Abstract: The solid-state reaction between epitaxial hcp-Co (110) and fcc-Co (001) thin films and Pd layers was investigated at annealing temperatures between 250 and 650 °C using X-ray diffraction and magnetic measurements. No significant intermixing of the layers occurs at annealing temperatures below 400 °C. For the atomic composition 1Co:1Pd after annealing at 450 °C the disordered solid solution fcc-Co_xPd_1-x is formed on the Pd/hcp-Co (110) and Pd/fcc-Co (001) interfaces. Epitaxial relationships CoPd (110)〈-111〉 || MgO(001)〈100〉 and CoPd (001)〈100〉 || MgO(001)〈100〉 between the nucleated disordered phase CoPd and the substrate MgO(001) were determined for Pd/hcp-Co (110) and Pd/fcc-Co (001) bilayers, respectively. The first magnetocrystalline anisotropy constant of the disordered CoPd phase ​​K₁^CoPd = - (1.8 ± 0.4)·10⁴ J/m³ for the (110) and (001) orientations was obtained.

Abstract: Silicon (Si) is currently the basis of most of nanodevice technology, therefore ultrathin materials based on Si have the great advantage of easy integration into existing circuitry. First flat silicon nanoparticles have been obtained with perfluorophenyl (PFPh) ligand coating. The size of these particles varied from 15 to 50 nm. Their thickness evaluated with the atomic force microscopy was about 3.3 nm. Based on ab initio DFT calculations we investigate the geometries and electronic structures of free-standing PFPh-stabilized 2D silicon in order to see if such systems have promising electronic and optical properties. We also examined the effect of doping PFPh-stabilized 2D silicon by the Mn atoms.

Abstract: Magnetoresistive effect and electrotransport properties of Fe-NbO (13 ≤ Fe, at.% ≤ 80) thin films annealed at 600 °C has been investigated. It has been established that the samples structure contains three main phases Fe, NbO₂, Fe_2.9O₄. Maximum of magnetoresistance in the samples does not exceed 0.3%, a coercive force is ranging from 150 to 370 Oe, depending on the Fe concentration. It is assumed that the films have a granular structure. Magnetoresistance and coercive force values, as well as the correlation between the magnetoresistance and the magnetization of the Fe-NbO samples are uncharacteristic for granular systems. It is assumed that uncharacteristic properties are due to the significant influence of ferrite Fe_2.9O₄ on the magnetic properties and electrotransport of the Fe-NbO films.

Abstract: Composite materials with Co (P) particles embedded into pores of silica and track etched polycarbonate membranes were fabricated by an electroless reduction. The magnetic and structural properties of the composite materials are characterized by scanning electron microscopy, X-ray diffraction, and vibrating sample magnetometer. The macroscopic and local magnetic anisotropy of the Co (P) particles electroless deposited in the pores of the polycarbonate membrane and silica is studied. The composite materials with linear pores exhibit uniaxial magnetic anisotropy. The easy axis lies along the Co (P) rods, the shape anisotropy dominates over the intrinsic crystalline anisotropy. Information on local anisotropy field and the grain size was obtained from investigation of approach to saturation magnetization law. The local anisotropy field for all the samples depends on P content. For Co (P) rods the local anisotropy value is also determined by nominal pore sizes. It was found that the investigated Co (P) rods is nanocrystalline. The effects of different pores morphology on the FMR-spectra characteristics are studied.

Abstract: The results of investigations of natural iron-chromium spinels of variable composition Fe²⁺(Cr_2-xFe_x³⁺)O₄ of the chromite-bearing Klyuchevskoi massif (Middle Urals), which are the main carriers of the magnetization of rocks are presented. Substantial changes in the composition and in magnetic structure of accessory chrome-spinels scattered in the host rock are established, unlike the almost unaltered ore-forming chrome-spinels, under the influence of secondary geological processes. To establish the connection between the chrome-spinel changes at the microlevel and features of the geomagnetic field anomalies created by this carrier of magnetization of rocks, it is carried out a complex of investigations of Fe-Cr-spinels (thermomagnetic analysis over the temperature range (4÷1000) K; magnetic resonance (MR) spectroscopy and magnetic force microscopy (MFM) in addition to magnetomineralogical studies). As a result, in the relict areas of grains of the accessory chrome-spinels were first discovered the magnetic clusters (superparamagnetic phases) in the form of single or groups of 2 – 3 magnetic dipoles of tens nanometers in size, or in the form of chain-like structures of magnetic dipoles/single domains.

Abstract: Structure and magnetic properties of FeNi/Ti multilayers prepared by magnetron sputtering were studied. The dependences of the spontaneous magnetization and hysteresis features of the films on the thickness of the magnetic layers were established. It was shown that these properties were to a large extent determined by interlayer interfaces, in which the effective magnetization decreases. The possible reason for the interface peculiarities was the interlayer mixing. The presence of (FeNi)Ti phase which was formed by the interdiffusion of FeNi and Ti layers was confirmed by X-ray diffraction measurements.

Abstract: The effects of inhomogeneous magnetization on optical second harmonic generation from magnetic nanostructures are studied. Cobalt triangular-shaped nanoparticles with vortex magnetization and magnetic trilayers that support the ferromagnetic phase formation are considered. We show that magnetic field dependencies of the SHG intensity for both types of structures reveal a number of distinct peculiarities associated with additional SHG mechanisms attributed to inhomogeneous magnetic state of the nanostructures.