A. D. Balaev

Magnetic properties of trigonal GdFe3(BO3)4

Abstract Field (0–70xa0kOe), temperature (4.2–350xa0K) and orientation dependencies of magnetisation and susceptibility of trigonal GdFe 3 (BO 3 ) 4 are presented. It is observed that the indirect exchange between rare-earth ions with large spin moment influences strongly the antiferromagnetic ordering. The spin–flop transition is specific for these crystals.

Magnetic properties of Fe3C ferromagnetic nanoparticles encapsulated in carbon nanotubes

The low-temperature dependences of magnetic characteristics (namely, the coercive force Hc, the remanent magnetization Mr, local magnetic anisotropy fields Ha, and the saturation magnetization Ms) determined from the irreversible and reversible parts of the magnetization curves for Fe3C ferromagnetic nanoparticles encapsulated in carbon nanotubes are investigated experimentally. The behavior of the temperature dependences of the coercive force Hc(T) and the remanent magnetization Mr(T) indicates a single-domain structure of the particles under study and makes it possible to estimate their blocking temperature TB = 420–450 K. It is found that the saturation magnetization Ms and the local magnetic anisotropy field Ha vary with temperature as ∼T5/2.

Study of Magnetic Correlations in Nanostructured Ferromagnets by Correlation Magnetometry

We propose a theoretically justified experimental magnetometric technique for determining the size of stochastic domains spontaneously formed in the spin system of nanostructured ferromagnets and for evaluating the effective anisotropy in these magnetically correlated regions. The method is based on monitoring the ΔM∼ H−2 relationship in the low-field part of the integral magnetization curve.

The Magnetic Structure of Ferromagnetic Filaments of a CoNi(P) Alloy in a Porous Silicon Matrix

The magnetic and resonance properties of CoNi(P) alloys, synthesized by chemical deposition as films on single crystal silicon substrates and as filaments in linear pores of porous silicon substrates, were studied by magnetization and ferromagnetic resonance measurements. It is established that CoNi(P) alloys of the same composition but different morphologies occur in states characterized by different degrees of nonequilibrium, which is manifested by different modes of the magnetization approach to saturation.

Effect of strontium and barium doping on the magnetic state and electrical conductivity of GdCoO3

A coordinated investigation of the magnetic and electrical properties of polycrystalline cobalt oxide compounds CdCoO3, Gd0.9Ba0.1CoO3, and Gd0.9Sr0.1CoO3 is carried out. Undoped GdCoO3 reveals a low conductivity; a magnetic moment of 7.4 μB per molecule, which is less than the theoretical value for the Gd3+ ion; and an asymptotic Curie temperature of −6 K. Doping GdCoO3 with barium and strontium to substitution of 10 at. % Gd brings about an increase in the conductivity and magnetic transitions at T = 300 K for Gd0.9Ba0.1CoO3 and T = 170 K for Gd0.9Sr0.1CoO3. The magnetization anomalies imply the formation of magnetic clusters. The behavior of the electrical conductivity at high temperatures suggests a variable activation energy. At low temperatures, Mott hopping conduction sets in.

Structural and Magnetic Characteristics of Fe/Si Bilayer and Multilayer Films Obtained by Thermal Deposition in Ultrahigh Vacuum

The structural and magnetic characteristics of Fe/Si bilayer and multilayer films with nanometer-thick layers obtained by thermal deposition in ultrahigh vacuum have been studied by methods of small-angle X-ray scattering, electron spectroscopy, and magnetometry. It is established that the mechanisms involved in the formation of Fe/Si and Si/Fe interfaces are different.

Magnetic Anisotropy in the Films of Oriented Carbon Nanotubes Filled with Iron Nanoparticles

Films of carbon nanotubes oriented perpendicularly to the substrate surface and filled with iron nanoparticles have been synthesized and studied. Morphological features of these nanocomposite films lead to the appearance of an easy magnetization axis, which is perpendicular to the film plane. A method for enhancement of this effect is suggested and successfully tested.

Multilayer Co/Pd films with nanocrystalline and amorphous Co layers: Coercive force, random anisotropy, and exchange coupling of grains

The values of saturation magnetization Ms, exchange coupling constant A, local magnetic anisotropy field Ha, random anisotropy correlation radius Rc, and coercive force Hc were independently measured for multilayer Co/Pd films with nanocrystalline and amorphous Co layers. It is shown that variation of the coercive force Hc(tCo) as a function of the cobalt layer thickness tCo is related to changes in characteristics of the magnetic microstructure. The main factor determining changes in the ferromagnetic correlation radius Rf and the average anisotropy 〈K〉 of a magnetic block in multilayer Co/Pd films is variation of exchange coupling constant A(tCo).

Effect of an electric field on the magnetization of a SmFe3(BO3)4 single crystal

A change in the magnetization of a SmFe3(BO3)4 single crystal in response to an applied alternating electric field has been experimentally observed for the first time. The measurements have demonstrated that the magnetization oscillates not only at a frequency of the applied electric field but also at twice the frequency. The dependences of the magnetoelectric effect on the magnetic and electric fields and temperature have been measured. It has been assumed that the existence of the second harmonic of the magnetoelectric effect is due to the electrostriction.

Frustration mechanism of formation of a helical magnetic structure in the CuB2O4 two-subsystem antiferromagnet

A new mechanism is proposed for forming an incommensurate magnetic structure of the transverse helix type owing to the removal of frustration through intersubsystem exchange in a two-subsystem antiferromagnet. The symmetry analysis of the distribution of the Dzyaloshinskii-Moriya interaction and comparison with the experimental data on the field dependence of magnetization indicate that antisymmetric exchange and competition between symmetric exchanges cannot be responsible for forming a helical magnetic structure in CuB2O4.