Papers by Author: G.V. Kurlyandskaya

Abstract: Thin Co films were fabricated by DC magnetron sputtering. The effect of argon pressure on the microstructure, surface morphology and magnetic properties of the samples was systematically studied. It was found that with the increase of argon pressure, the sharpness of the crystalline texture of the samples declines, the roughness of film surfaces and the coercivity of the films increase. Based on these results, a Co/Cu/Co pseudo spin-valve system was designed and the corresponding structures were fabricated. The difference in coercivity of magnetic layers was obtained by deposition of the Co layers at different Ar pressures. Change of the resistance of this trilayer is induced at a moderate field by the spin rotation in the soft layer with lower coercivity.

Abstract: Magnetic nanoparticles (MNPs) were produced by the electric explosion of wire method (EEW) using (Co_0.94Fe_0.06)_72.5Si_12.5B₁₅ and Fe₇₈Si₉B₁₃ amorphous wires. The wires were exploded in Ar atmosphere at 0.12 MPa. After the explosion the surface of all produced nanoparticles was passivated with oxygen. The produced MNPs are spherical low aggregated particles with average size below 37 nm and rather narrow size distributions with geometric standard deviation less than 1.7. Both materials are multiphase and contain up to 23 wt % of amorphous phase.

Abstract: Magnetization and magnetoresistance (MR) studies were carried out on the [Gd/T_n multilayers with different thickness of Gd and Ti layers prepared by magnetron sputtering. The temperature interval of measurements was from 2 to 300 K, for the highest available magnetic field value of 100 kOe. A negative magnetoresistance was observed in all samples. The observed negative MR was analysed by using different magnetoresistance models.

Abstract: The role of the geometrical parameters was studied for thin film based [FeNi (100 nm)/Cu (3 nm)]₄/FeNi (100 nm)/Cu (500 nm)/[FeNi (100 nm)/Cu (3 nm)]₄/FeNi (100 nm) magnetoimpedance elements with open magnetic flux prepared by lithography technique. The maximum magnetoimpedance sensitivity of 17 %/Oe was obtained for meander shaped sample, exceeding the value of the maximum sensitivity of 5 %/Oe of the single stripe sample. The highest values of the magnetoimpedance were observed for relatively low frequency of order of 50 MHz convenient for technological applications. Both developed technology and obtained results can be useful for optimization of the design of miniaturized detectors of small magnetic field.

Abstract: Magnetic properties and giant magnetoimpedance (GMI) of CuBe/Fe₂₀Co₆Ni₇₄ electroplated wires was studied for frequency of 1 MHz and the amplitude of the driving current of 20 mA with focus on the development of magnetic field detectors of particular types. The possibility of quantitative ferrofluid concentration measurements was demonstrated. GMI of electroplated wire can be useful for the study of the dynamic properties of the ferrofluid. GMI of the electroplated wires in the non-uniform field created by the permanent magnet was studied in the configuration adapted for automatic control lines, machinery control, and positioning systems.

Abstract: NiCuZn ferrites were prepared by the sol-gel self-combustion method. Nanosized, homogeneous and highly reactive powders were obtained at relatively low temperatures. In present work the variations of structural, magnetic, and microwave properties of NiCuZn ferrite nanoparticles were studied as a function of the annealing temperature. The analysis of XRD patterns showed that only the spinel phase is present. Cell parameters slightly vary with thermal treatment while a crystalline size increases. Magnetic nanoparticles were mixed with an epoxy resin for reflectivity studies with a microwave vector network analyzer using the microwave-guide method in the range of 7.5 to 13.5GHz. Static saturation magnetization value (measured by SQUID) and microwave absorption show clear dependence on the annealing temperature/particle size and the absorption maximum moves towards the higher frequencies with an increase in the average size of the particles.

Abstract: The magnetoimpedance (MI) in thin films and magnetic multilayers has been extensively studied in recent years. One of the important problems which is still under discussion is the temperature dependence of MI of the multilayered nanostructures for temperatures up to 200 oC. In this work magnetic properties and temperature dependence of the magnetoimpedance of Fe19Ni81/Cu/Fe19Ni81 multilayers with opened and closed magnetic pathes were studied and comparatively analyzed for the functional temperature interval of + 23 oC to + 160 oC.

Abstract: Structure and magnetic properties of nanoscale [Gd/Ti]n multilayers prepared by rf-sputtering are studied. It is found that the decrease in the Gd layer thickness LGd leads to beginning of the structure transformation in Gd layers from the fine-crystalline to amorphous state when LGd becomes less than 2 nm. The Curie temperature TC decreases as a function of the Gd layer thickness in the same way as in early studied epitaxially grown Gd films, i.e. in case for which the finite-size effect plays most important role. A deviation of the TC(LGd) behaviour at very low LGd from the fit according to the finite-size law is probably caused by the island-like structure of the Gd layers.

Abstract: FeNi films were deposited by DC magnetron sputtering at different Ar pressures. The structure and magnetic properties of the FeNi films are affected by the Ar pressure. Ferromagnetic resonance (FMR) measurements were done at a frequency of about 8.85 GHz. Both the value of resonance field and resonance line width show strong dependence on the Ar pressure: the lowest value of the resonance field and the narrowest resonance width correspond to the smallest argon pressure. Increase of the Ar pressure causes the films to have a significant perpendicular anisotropy with the easy axis pointing out of the plane. The magnetic properties and FMR were also studied for the [FeNi(170 nm)/Ti]n/FeNi(170 nm) (n = 1, 2, 5) structures prepared at the smallest Ar pressure. The FMR studies showed that the obtained multilayers are very robust: the value of the resonance field and resonance line width of the [FeNi/Ti]n/FeNi multilayers are very close to the corresponding values for the FeNi films.

Abstract: In this work magnetoimpedance (MI) behaviour was studied experimentally for Fe19Ni81(175 nm)/Cu(350 nm)/Fe19Ni81(175 nm) sensitive elements deposited by rf-sputtering. A constant magnetic field was applied in plane of the sandwiches during deposition perpendicular to the Cu-lead in order to induce a magnetic anisotropy. Sandwiches with different width (w) of FeNi parts were obtained. The complex impedance was measured as a function of the external magnetic field for a frequency range of 1 MHz to 700 MHz for MI elements with different geometries. Some of MI experimental data are comparatively analysed with finite elements numerical calculations data. The obtained results can be useful for optimization of the design of miniaturized MI detectors.