Magnetic anisotropy of the VBO<Subscript>3</Subscript> and CrBO<Subscript>3</Subscript> transition-metal borates

Temperature and field dependences of the magnetization of VBO₃ and CrBO₃ single crystals with the magnetic field applied parallel and perpendicular to the (111) basal plane were measured. VBO₃ was found to have a considerable uniaxial anisotropy with a field H_a≈6.25 T. CrBO₃ was shown to exhibit not only uniaxial but also hexagonal anisotropy. The experimental anisotropy constants were estimated, and their temperature dependences are presented.     

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.     

Magnetic properties of La0.7Sr0.3MnO3 manganite films obtained by extraction pyrolysis

The structural and magnetic properties of manganite films obtained for the first time by extraction pyrolysis have been experimentally investigated. It has been established that at annealing temperatures T ≈ 600 K the films are fine-grained and have spin-glass-like magnetic properties. Prolonged annealing at T ≥ 700 K results in grain overgrowth and ferromagnetic behavior.     

Magnetoresistance hysteresis in granular HTSCs as a manifestation of the magnetic flux trapped by superconducting grains in YBCO + CuO composites

Hysterestic behavior of the magnetoresistance of granular HTSCs and its interaction with the magnetic hysteresis are studied by measuring magnetoresistance R(H) and critical current I _c(H) of composites formed by HTSC Y_0.75Lu_0.25Ba₂Cu₃O₇ and CuO. A network of Josephson junctions is formed in such composites, in which the nonsuperconducting component plays the role of barriers between HTSC grains. Hysteretic dependences R(H) of magnetoresistance are studied in a wide range of transport current density j and are analyzed in the framework of the two-level model of a granular superconductor, in which dissipation takes place in the Josephson medium and the magnetic flux can be pinned both in grains and in the Josephson medium. The interrelation between the hysteresis of critical current I _c(H) and the evolution of the hysterestic dependence R(H) of the magnetoresistance upon transport current variation is demonstrated experimentally. The effect of the magnetic past history on the hysteretic behavior of R(H) and the emergence of a segment with a negative magnetoresistance are analyzed. It is shown for the first time that the R(H) dependences are characterized by a parameter that is independent of the transport current, viz., the width of the R(H) hysteresis loop.     

Influence of transport current and thermal fluctuations on the resistive properties of HTSC+CuO composites

Measurements of the temperature dependence of the electrical resistance R(T) below the superconducting transition temperature have been performed at different values of the transport current in HTSC+CuO composites modeling a network of weak S-I-S Josephson junctions (S—superconductor, I—insulator). It has been shown experimentally that the temperature dependence R(T) at different values of the transport current is adequately described by means of the mechanism of thermally activated phase slippage developed by Ambegaokar and Halperin for tunnel structures. Within the framework of this model we have numerically calculated the temperature dependence of the critical current J _c(T) as defined by various criteria. Qualitative agreement obtains between the measured and calculated temperature dependences J _c(T). Fiz. Tverd. Tela (St. Petersburg) 41, 969–974 (June 1999)     

Features of the Pulsed Magnetization Switching in a High-Coercivity Material Based on ε-Fe2O3 Nanoparticles

Physics of the Solid State - The magnetic structure of the ε-Fe2O3 iron oxide polymorphic modification is collinear ferrimagnetic in the range from room temperature to ~150 K. As the...     

Features of Relaxation of the Remanent Magnetization of Antiferromagnetic Nanoparticles by the Example of Ferrihydrite

Physics of the Solid State - The relaxation of the remanent magnetization of antiferromagnetically ordered ferrihydrite nanoparticles at the exchange bias effect implemented in these systems has...     

Temperature of the Magnetic Ordering of the Trivalent Iron Oxide ε-Fe2O3

Physics of the Solid State - The trivalent iron oxide ε-Fe2O3 is a fairly rare polymorphic iron oxide modification, which only exists in the form of nanoparticles. This magnetically ordered...