Magnetic transition in Co/(Gd–Co) multilayers

[Co/Gd_0.36Co_0.64]₄/Co multilayers with Co termination layer have been prepared by rf sputtering. They form macroscopic ferrimagnets with a compensation temperature (T_comp) determined by the thickness ratio of the layers. In low fields the magnetization of Co and Gd–Co layers are along the axis of the applied field. Increasing field makes the moments of both the Co and Gd–Co layers deviate from the axis of the field giving rise to a transition into a twisted state. These magnetic transitions were studied by vibrating sample magnetometer (VSM), magneto-optic Kerr effect and magnetoresistance measurements at various temperatures. The nucleation and evolution of surface- and bulk-twisted magnetic states were also observed in these multilayers.     

Hysteretic properties of nanostructured terbium films

The hysteretic properties of terbium films subjected to layered structuring by introducing nonmagnetic Ti and Si layers of a fixed thickness (2 nm) are studied in the temperature range 2–230 K. It is found that the variation of the Tb layer thickness in the range 1.5–360 nm and the nonmagnetic layer material leads to substantial changes in the magnetic hysteresis of the films and its temperature behavior. These changes are related to a change in the structural composition of the films, which consists of nanocrystalline, granulated, and amorphous Tb phases.     

X-ray study of the dispersion and pore structure of the HgCl2-active carbon catalytic system

In the HgCl₂-active carbon system, the salt component is located in the mesopores and blocks the micropores of the support. Mercuric chloride is primarily in a molecularly disperse state, and 10–15% of the salt component is aggregated in clusters with diameters of 0.5–5.5 nm. The size of the clusters is a function of the type of application of the salt component. The mobility of the salt clusters and their growth in the conditions of the reaction were determined. The process of evaporation of mercuric chloride is accelerated with an increase in the size of the clusters. An increase in the dispersion of the salt phase up to a molecular distribution results in stabilization of the HgCl₂-active carbon catalytic system.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2420–2424, November, 1989.     

Spin-valve magnetoresistive structures based on Co/Tb multilayer films

The effect of the layer thickness on the magnetic properties of {Co/Tb}_n, {Co/Tb}_n/Co, and {Co/Tb}_n/Co/Cu/Co multilayer films is studied. The dependence of the hysteresis and magnetoresistive properties of {Co(1 nm)/Tb(1 nm)}_n/Co(5 nm)/Cu(L _Cu)/Co(5 nm) structures on the thickness of the {Co/Tb}_n layer and copper spacing are obtained. The feasibility of spin-valve structures based on {Co/Tb}_n multilayer films with in-plane anisotropy is demonstrated.     

Magnetic impedance of structured film meanders in the presence of magnetic micro- and nanoparticles

The magnetic impedance (MI) of film elements in the form of meanders with a [Fe19Ni81]/Cu]₄/Fe19Ni81/Cu/[Fe19Ni81/Cu]₄/Fe19Ni81 layered structure and variable geometry is studied. For the best meanders (having a maximal MI of up to 125% and an MI maximal sensitivity of about 30%/Oe), the influence of stray magnetic fields is determined. The stray fields are produced by spherical iron particles 500 μm in diameter and ferrofluids containing iron oxide nanoparticles. The feasibility of detecting intricately configured stray fields from a set of ferromagnetic spheres arranged on the surface of an MI element is demonstrated. The sensitivity of film meander MI elements to nonuniform external magnetic fields is simulated. The results of this work may be helpful in developing special-purpose magnetic sensors intended for micropositioning, nondestructive testing, and biomagnetic detection.     

Magnetic properties of electroplated wires coated by ferrofluid

Low-frequency magnetic properties of ferromagnetic composite wires were studied with and without coating by ferrofluid. Non-magnetic CuBe wires of 0.1 mm diameter were electroplated with FeCoNi layer of 1 μm thickness. Magnetization curves were measured in the frequency range of 10 Hz–3 kHz. The composite CuBe/FeCoNi/ferrofluid material shows a hysteretic behaviour in a small field. The hysteresis loop of ferrofluid covered electroplated wire is not a simple sum of the ferrofluid “wire” plus non-covered wire signals. It indicates an interaction between magnetic wire and ferrofluid which can be revealed by low-frequency measurements. The combination “electroplated wire/ferrofluid” can be considered as a new type of composite magnetic material consisting of solid magnetic core coated by complementary liquid magnetic material. Low-frequency measurements in presence of ferrofluid can be a useful method to study magnetic properties of ferromagnets.     

Magnetic Properties of Iron Oxide Nanoparticles Obtained by Laser Evaporation

Russian Physics Journal - The paper concentrates on a synthesis of spherical magnetic particles obtained by laser evaporation under various process conditions. Depending on the process conditions,...     

Induced magnetic phase transitions in GdCo/Co-type multilayer films

The magnetic structure transformation of the layered ferrimagnet [Co/Gd₃₆Co₆₄]₄/Co in an external magnetic field was comprehensively studied. Using magnetometrical, magnetooptical, and magnetoresistive techniques, it is established that, when magnetized in fields exceeding a threshold value H _cr, the collinear magnetic structure formed by the magnetic moments of the Co and GdCo layers is distorted. The value H _cr varies nonmonotonically with temperature T and reaches a minimum at the temperature of magnetic compensation of the layered ferrimagnet. The H _cr(T) dependence is well described in terms of the homogeneous ferrimagnet model with an adequately chosen phenomenological intersublattice interaction constant taking into account the weakened coupling of the surface Co layers with the internal part of the actual layer structure.     

Specific Features of the Properties of Co–Cu Granular Media Caused by the Structure of the Material

A comparative analysis of rapidly quenched strips and thin films prepared from Co–Cu alloys with giant reluctance is performed. It is established that their microstructure and phase composition differ strongly. Precipitates of Co-enriched phase of two types that differ in their origin and sizes are present in strips. Large particles (100 nm) having the fcc structure determine the magnetic properties, and small particles ( 5 nm) determine the reluctance. In films, Co particles of only one type are detected. They have hexagonal close-packed lattice, can be in superparamagnetic and ferromagnetic states, and yield the corresponding contributions to the giant reluctance. The above-indicated specific features in the microstructure lead to different magnetic and reluctance properties of strips and films.