G.V. Kurlyandskaya

Magnetic Properties and Magnetoimpedance of Electroplated Wires

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.

Temperature dependence of the magnetic properties and magnetoimpedance of nanocrystalline Fe73.5Si16.5B6Nb3Cu1 ribbons

The temperature dependences of the magnetic properties and the magnetoimpedance effect of soft magnetic nanocrystalline Fe73.5Si16.5B6Nb3Cu1 alloy ribbons are studied in the temperature range 24–160°C. A high temperature sensitivity of the impedance and the magnetoimpedance effect of the ribbons are detected in the ac frequency range 0.1–50 MHz. At an ac frequency of 50 MHz, the change in the impedance reaches 0.2 Ω/°C (0.5%/°C) in the temperature range 85–160°C. When the temperature increases, a monotonically decreasing character of the dependence of the magnetoimpedance effect on the applied magnetic field changes into a dependence having an increasing initial segment. The effect of temperature on the magnetoimpedance properties of the soft magnetic nanocrystalline ribbons is shown to result from temperature-induced changes in their electrical conductivity, magnetization, and effective magnetic anisotropy.

Structure and Magnetic Properties of Gd/Ti Nanoscale Multilayers

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.

Structural and Magnetic Properties of Nanoparticles of NiCuZn Ferrite Prepared by the Self-Combustion Method

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.

FeNi-Based Film Nanostructures for High Frequency Applications: Design and Characterization

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.

Magnetoimpedance of FeNi Thin Film Meanders

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.

Magnetoresistive Properties of Tb/Ti and Tb/Si Multilayers

Magnetic, magnetoresistive and structural properties of Tb/Ti and Tb/Si nanoscale multilayers prepared by alternative deposition of Tb layers and Ti or Si spacers are comparatively studied. It was concluded that spin disorder scattering is responsible for the negative longitudinal magnetoresistance observed in multilayers of both types.

High Frequency Magnetoimpedance of FeNi/Cu/FeNi Sensitive Elements with Different Geometries

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.

Circular Magnetization Processes in CoFeNi Electroplated Wires

Circular magnetization processes in electroplated wires is an important topic having straight connection with sensor applications of these soft magnetic materials. In present work the longitudinal and circular hysteresis loops were measured and corresponding magnetization processes were studied in Cu98Be2/Co16Fe20Ni64 wires. The longitudinal hysteresis loops, Mz-Hz, were measured by inductive technique in a frequency range of 10 to 70 Hz. The circular magnetization curves (Mφ- Hφ) were measured for frequencies of 50 and 100 kHz in the Hφ field up to 1500A/m for different values of the axial external field of 0 to 500 A/m. The longitudinal and circular magnetization curves are comparatively analyzed.

Co/Cu/Co Pseudo Spin-Valve System Prepared by Magnetron Sputtering with Different Argon Pressure

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.