Papers by Keyword: Exchange Interaction

Abstract: Magnetic properties of the R₂Fe₁₇ compounds are sensitive to the atomic substitutions and interstitial absorption of nitrogen. In our work, both were combined and their effect on the magnetization behavior of Er₂Fe₁₇ compound in magnetic fields up to 58 T was studied. Er₂Fe₁₇N₂, Sm_1.2Er_0.8Fe₁₇N₂ and Sm_1.8Er_0.2Fe₁₇N_2.1 nitrides were prepared. Magnetization measurements were carried out, mainly on powder samples (excluding Er₂Fe₁₇ single crystal). Nanopowders of Sm_1.2Er_0.8Fe₁₇N₂ were obtained by mechanical grinding. The grinding time was varied from 0 to 60 minutes. The strength of the inter-sublattice coupling in samples is estimated by analyzing high-field magnetization data.

Abstract: Theory of electronic and optical properties of excitonic states confining in Si nanocrystals is presented. The electron and hole states are numerically computed using the atomistic empirical tight-binding Hamiltonian including the spin-orbit coupling together with the first nearest-neighboring interaction. We theoretically study the electron-hole interactions in spherical silicon hydrogenated nanocrystals by incorporating coulomb and exchange interaction into the empirical tight-binding model. The comparisons of coulomb and exchange energies with empirical pseudopotential method (EPM), tight-binding method (TB), effective-mass approximation (EMA) and ab initio calculations are quantitatively realized. Finally the energies of the excitonic ground states obtained from diagonalizing the tight-binding configuration-interaction scheme are in a good agreement with other theoretical and experimental data.

Abstract: A new method of intergrain exchange interaction energy determination in nanostructured magnetically hard alloys with spontaneous spin-reorientation transition has been developed and verified. It is based on the knowing of the material magnetic anisotropy constants values at its “easy cone” state and the external negative magnetic field strength H, which reversibly “tears” the exchange coupling between nanograins. It should be more than exchange field and smaller than coercivity value. Using this method the exchange interaction energy parameter for MQP-B+ alloy was estimated. Its value is in agreement with estimated one by FMR technique for film system Fe-Nd₂Fe₁₄B and close to that obtained from the remanent magnetization temperature dependences measurements in negative magnetic fields.

Abstract: The Tm₂Fe_19-xMn_x (x = 0 - 1.5) and Tm₂Fe₁₆, Tm₂Fe₁₇, Tm₂Fe₁₈, Tm₂Fe₁₉ intermetallic compounds were synthesized and their magnetic and structural properties were studied. Magnetic measurements, X-ray and neutron diffraction investigations were used. The compounds crystallize in a disordered variant of the hexagonal Th₂Ni₁₇-type structure. The lattice parameters a, c increases in the Tm₂Fe_19-xMn_x system, whereas c decreases and a increases in the Tm₂Fe₁₉ - Tm₂Fe₁₆ system as Fe content decreases. The temperatures of ferromagnetic ordering and spin-reorientation increase as Fe content decreases in these systems. Apparently, the decrease of occupation of defected dumbbell Fe (4e) site causes these regularities.

Abstract: Morphology and structure of the interface in Ni/Ge thin films being due to the mutual diffusion of these elements are investigated with the help of atomic force microscope, high resolution electron microscope and micro-diffraction. Strong effect of interface in magnetic behavior of Ni layers is demonstrated and explained by formation of magnetic order in the interface and rough boundaries between layers.

Abstract: Magnetic spin valve structures have a great practical interest as sensors of magnetic fields, hard disk read heads and elements of magnetic random access memories (MRAM). Despite the large number of experimental and theoretical work on spin valve structures, the effects of interlayer interactions occurring in these structures, at present time are not fully understood. Introduction

Abstract: We reported magnetooptical properties of Tb³⁺ in single crystals of Tb₃Fe₅O₁₂ and Tb₃Ga₅O₁₂ for ion occupying sites of D₂ symmetry in the garnets structure. It is shown that in the employed Voigt geometry the magnetic linear birefringence and the dichroism reach values 10^-4, and have a strong dependence on the wavelength and a strong anisotropy. The absorption spectra were obtained at temperatures of 30K, 100K using magnetic field up to 25 kOe applied parallel and perpendiculare to the electric vector E linearly polarized light on the ⁷F₆ ⁷F₀ and ⁷F₆ ⁷F₁ optical transitions region. The aim of this research was revealing of a role of contributions of exchange interaction and a crystal field in splitting of energy levels of the basic condition ⁷F₆ ion Tb³⁺ multiplet in Tb ferrite-garnet by studying of character of spectra magnetic linear dichroism (MLD) paramagnetic and ferrimagnetic crystals placed in an external magnetic field. More over, the assumption about nonreciprocity of magnetic linear birefringence (MLB) spectra and dichroism with the change of the relative orientation of the magnetization vector I and the light wave vector has been experimentally confirmed. This effect may use as a base for the design of the different transducers, for example, magnetooptical optical channels commutator.

Abstract: A novel model consisting of basic micro-processes has been developed on the basis of the classic diffusion theory. It is first time that the concept of exchange rate has introduced，and the growing process of surfactant-mediated epitaxial thin-film growth has been simulated with Kinetic Monte Carlo (KMC) technique. The results of simulation found that the exchange reaction of RLA model is a combination of the basic micro-processes. The majorities of exchange are not complete position exchange and the exchange rate doesn’t always equal one. Both surfactant atoms and adatoms would diffuse from one layer to another. The diffusion happens mostly between single atoms and the diffusing atoms increase with substrate temperature.

Abstract: Phase transitions and critical phenomena are investigated within a two-sublattice model. In the framework of the random fields with the exchange interaction method the system of equations is obtained. It allows us to establish conditions under which magnetic phase transitions are possible. Critical concentration of ferromagnetic atoms which is necessary for the existence of ferromagnetic, ferrimagnetic and antiferromagnetic phases is determined.

Abstract: By measuring the angular dependence of ferromagnetic resonance field at room and low temperatures, it is demonstrated that the magnitude of magnetic field applied during magnetron deposition of Ta/F/AF/Ta structures, where F=Co, NiFe and AF=FeMn and IrMn, influences the uniaxial and unidirectional anisotropy, magnetization and the exchange bias blocking temperature. The deposition field effects on the bilayer structure are compared with the effects on a similar structure, but without antiferromagnetic layer. The exchange bias blocking temperature of investigated structures is found to be significantly lower than the Néel temperature of a bulk antiferromagnet. The origin of the observed effects is shortly discussed.