Microwave response to the magnetization switching of CoFeB/Ta/CoFeB spin valves and CoFeB films

Negative magnetoresistance modifying the quality factor of a microwave cavity under the magnetization switching of ferromagnetic layers has been discovered in a MgO/CoFeB/MgO/Ta film with a single ferromagnetic layer and a MgO/CoFeB/Ta/CoFeB/MgO/Ta spin valve consisting of two ferromagnetic CoFeB layers. The dependence of the first derivative dP/dH of the microwave absorption signal on the dc magnetic field of the spectrometer exactly reproduce the magnetic hysteresis loops of the sample. The slope of these dependences and the amplitude of dP/dH jumps under remagnetization of the layers are determined by the interplay of a negative magnetoresistance of individual layers and a positive giant magnetoresistance of the entire multilayer structure. The discovered phenomenon allows using microwave absorption for making a high-sensitivity contact-free indicator of the basic magnetization states of a spin valve.     

Magnetic properties of the tetranitrosyl-iron complex Fe<Subscript>2</Subscript>(SC<Subscript>3</Subscript>H<Subscript>5</Subscript>N<Subscript>2</Subscript>)<Subscript>2</Subscript>(NO)<Subscript>4</Subscript>

The magnetic properties of the binuclear nitrosyl-iron complexes Fe₂(SC₃H₅N₂)₂(NO)₄ are investigated. It is demonstrated that several types of particles, such as dimers with a pair of spins 1/2, dimers with a pair of spins 5/2, and paramagnetic particles with spin 3/2, make a contribution to the magnetic properties of the complexes. A decrease in the temperature below 25 K leads to a change in the shape of the EPR spectra corresponding to these dimers, so that Lorentzian lines (homogeneous broadening) transform into Gaussian lines (inhomogeneous broadening). This is accompanied by a stepwise change in the EPR line width and g factors. The change in the line shape indicates that complexes become asymmetric at low temperatures, possibly, due to the decrease in the spin exchange frequency below the frequency of the microwave field of the spectrometer.     

Contributions of Magnetic Phases to the FORC Diagram in (NdDy)(FeCo)B Magnets

Physics of the Solid State - The relationship of the micromagnetic structure, the contributions of various crystalline phases and hysterons obtained by the first order reversal curves (FORC) method...     

Thermodynamic and kinetic aspects of the weakening of ionic crystals by pulsed magnetic fields

The effect of short (10⁻² s) magnetic-field pulses (B=7 T) on the plastic flow of ionic crystals is investigated. The stages of the transition process stimulated by a field in the system of structural defects of the lattice are distinguished. The results are discussed from the standpoint of the thermodynamics and kinetics of processes in nonequilibrium systems. Fiz. Tverd. Tela (St. Petersburg) 39, 2016–2018 (November 1997)     

Acoustic tomography of dynamic processes in a sea shelf zone with the use of complex signals

Experimental data are presented on the use of single receiving and transmitting systems in acoustic tomography of dynamic processes in a shallow sea. The experiments are based on the use of the transmission tomography and opposite-direction sounding with complex phase-manipulated signals. The original data are those obtained by the authors in 1990–2000 on the shelf of the Sea of Japan near the Gamov Peninsula, in the vicinity of the acoustical-hydrophysical experimental site of the Pacific Oceanological Institute. A possibility of using combined transmitting-receiving systems (transceivers) for monitoring the temperature and fields of currents in the ocean is demonstrated.     

Study of how hydrological conditions affect the propagation of pseudorandom signals from the shelf in deep water

The paper examines how hydrological conditions affect manifestation of the acoustic “landslide” effect, which consists in focusing of acoustic energy in the near-bottom layer on the shelf and its transition to the axis of an underwater sound channel in deep water. We compare the results of experiments performed in the Sea of Japan in April 2014 and August 2006 on the same acoustic track, where the distance between corresponding points was more than 100 km. In April, the hydrological conditions in the shelf region of the track and in the upper layer of the deep-water part of the sea were characterized by the presence of a relatively weak (~0.35 s^–1) negative vertical sound velocity gradient, whereas in August 2006, it was ~1.5 s^–1. Experimental and numerical studies showed that the acoustic landslide effect also manifests itself under conditions of a weak negative sound velocity gradient, but the structure of the acoustic field trapped by the underwater sound channel has a more complex character with a time-expanded pulse characteristic. Nevertheless, its ordered, stable, and well-identified structure at all track points chosen for measurements make it possible to reliably create an efficient (with accuracies to hundredths of a percent) underwater navigation systems like GLONASS and GPS for the spring hydrology season.     

Magnetic noise as the cause of the spontaneous magnetization reversal of RE–TM–B permanent magnets

The relation between the macroscopic spontaneous magnetization reversal (magnetic viscosity) of (NdDySm)(FeCo)B alloys and the spectral characteristics of magnetic noise, which is caused by the random microscopic processes of thermally activated domain wall motion in a potential landscape with uniformly distributed potential barrier heights, is found.     

Effect of samarium impurity on the relaxation of the magnetization of a (NdDy)(FeCo)B alloy

Small Sm additions (~1–3 at %) have been found to slow down the relaxation of the magnetization in a magnetic field in the (NdDy)(FeCo)B alloy by several times. The effective “freezing” of the spontaneous relaxation of the magnetic moment is related to the substantial increase in the potential barriers for motion of domain walls when introducing Sm ions that have other symmetry of the single-ion anisotropy than that of Nd and Dy ions. The results can be used to stabilize the properties of hard magnets.     

Magnetosensitive reactions in ionic crystals during their plastic deformation

A new method for investigating spin-independent chemical reactions between radical centers at point defects and dislocations in solids is proposed. The method is based on studying the mobility of dislocations in a field of mechanical stresses. The application of a magnetic field with inductionB=1 T results in a change in the state of the defects of the crystal lattice in ionic crystals, which can be observed a long time (up to 10³ s) after switching off the field. Radical reactions were analyzed in which the kinetics of changes in the magnetic field can cause the effect of magnetic “memory” in distorted microregions of the lattice. Translated fromIzvestiya-Akademii Nauk Seriya Khimicheskaya, No. 4 pp. 739–744, April. 1997.     

Changes in the Ferromagnetic Resonance Spectra and Magnetic Anisotropy of the [CoFeB/SiO2|Bi2Te3]47 Multilayer Heterostructures upon the Deposition of Fe/Fe3O4 Nanoparticles on Their Surface

Physics of the Solid State - An increase in the anisotropy constant of the [CoFeB/SiO2|Bi2Te3]47 heterostructure under the influence of magnetic Fe/Fe3O4 nanoparticles deposited on the surface of...