Effect of severe plastic deformation on the electronic properties of the Cu<Subscript>72</Subscript>Au<Subscript>24</Subscript>Ag<Subscript>4</Subscript> alloy

The electrical, magnetic, and optical properties of the Cu₇₂Au₂₄Ag₄ ternary alloy in the ordered and disordered states have been studied by the method of severe torsional plastic deformation under pressure in Bridgman anvils. It has been shown that, as a result of this deformation, the residual electrical resistivity of the alloy increases by approximately 11% and the magnitude of the negative thermopower decreases. The high diamagnetic susceptibility of the alloy has been explained by a significant role of charge carriers with the effective mass considerably smaller than the free-electron mass. The behavior of the optical conductivity has been discussed with due regard for the results of energy-band calculations. The experimental data obtained for the Cu₇₂Au₂₄Ag₄ alloy have been compared with the results of similar studies of the Cu₃Au binary alloy.     

Effect of plastic deformation on the electronic properties of the Cu<Subscript>60</Subscript>Pd<Subscript>40</Subscript> alloy

The effect of severe plastic deformation by torsion under Bridgman anvil pressure (SPDT) on the electrical, magnetic, and optical properties of the Cu₆₀Pd₄₀ alloy was studied. It is shown that, after the alloy is disordered, the Curie-Weiss constants of the paramagnetic component are changed insignificantly. In this case, the temperature-independent negative component of the magnetic susceptibility decreases more than fivefold. The electrical resistance and negative thermopower, on the contrary, increase severalfold as a result of SPDT. The character of the optical conductivity is discussed using the band structure calculation results.     

Magnetic properties of an easy-plane trigonal NdFe<Subscript>3</Subscript>(BO<Subscript>3</Subscript>)<Subscript>4</Subscript> antiferromagnet

The field and temperature dependences of magnetization and the temperature dependences of the initial magnetic susceptibility have been theoretically studied for three crystallographic directions in a trigonal NdFe₃(BO₃)₄ antiferromagnetic crystal. The calculations were performed using a molecular field approximation and a crystal field model for the rare-earth subsystem. The obtained theoretical expressions are applied to the interpretation of recent experimental data [1–4] on the magnetic properties of NdFe₃(BO₃)₄. The results of calculations show a good agreement with experiment. The proposed theory adequately describes (i) anomalies of the Schottky type in the temperature dependence of the magnetic susceptibility, (ii) nonlinear curves of magnetization in the basal plane in a magnetic field up to 1 T (showing evidence of the first-order phase transitions) and their evolution with the temperature, and (iii) the field and temperature dependences of magnetization in a magnetic field up to 9 T.     

Structure and mechanical properties of Ni<Subscript>3</Subscript>Ge single crystals under severe plastic deformation and heating

Mechanical tests are performed for Ni₃Ge alloy single crystals in the intense plastic shear deformation scheme under quasi-hydrostatic pressure at different test temperatures. Dependences of resistance to shear deformation on the Bridgman anvils’ angle of rotation are obtained. The microrelief of the surface damage of Ni₃Ge single crystals fractured by plane bending after specimens were withdrawn from the Bridgman anvils is studied. X-ray diffraction patterns of deformed Ni₃Ge single crystals are obtained.     

Effect of atomic ordering on the role of grain boundaries in the plastic deformation of Ni<Subscript>3</Subscript>Fe alloy

The structure of dislocations and the defect structure of grain boundaries and their parameters in Ni₃Fe alloy with short-range order (SRO) and long–range order (LRO) at different stages of plastic deformation are studied by means of transmission diffraction electron microscopy using thin foils and replicas. It is found that atomic ordering reduces the Σ3 twins plasticizing effect, increases the density of grain boundary defects, slows their annihilation during deformation, and intensifies the microstrains at the triple junctions of grain boundaries.     

Effect of plastic deformation on physical properties and structure of the shape memory alloy Ti<Subscript>49.5</Subscript>Ni<Subscript>50.5</Subscript>

The effect of severe plastic deformation by torsion (SPDT) in Bridgman anvils at a high pressure (6 GPa) on the physical properties and crystal structure of the shape memory alloy Ti_49.5Ni_50.5 has been studied. The behavior of the thermal expansion, electrical resistivity, absolute differential thermopower, Hall coefficient, magnetic properties, and optical characteristics of the amorphous/nanocrystalline and submicrocrystalline alloys obtained by the SPDT with subsequent heat treatment at 800 K has been discussed.     

Nanocrystallization of an amorphous Fe<Subscript>80</Subscript>B<Subscript>20</Subscript> alloy during severe plastic deformation

The structural evolution of an amorphous Fe₈₀B₂₀ alloy subjected to severe plastic deformation at room temperature or at 200°C was studied. Deformation leads to the formation of α-Fe nanocrystals in an amorphous phase. After room-temperature deformation, nanocrystals are localized in shear bands. After deformation at 200°C, the nanocrystal distribution over the alloy is more uniform. Possible causes of the crystallization of the amorphous phase during severe plastic deformation are discussed.     

Microstructure,phase transformations,and properties of a Cu<Subscript>3</Subscript>Pd alloy subjected to severe plastic deformation

The structure of a preliminary ordered Cu₃Pd alloy, both with layered and columnar periodic structures, subjected to severe plastic deformation with twist extrusion with subsequent annealing, has been investigated using transmission electron microscopy; X-ray diffraction; and measurements of the resistance, magnetic susceptibility, and microhardness. The purpose of this study is the formation of nano-and submicrocrystalline structures in this alloy in order to improve the strength properties, with conservation of the ordered state determining the high conductivity of the alloy.     

Magnetic properties of ordered nanowires of the quasi-two-dimensional antiferromagnet SpFeMn(C<Subscript>2</Subscript>O<Subscript>4</Subscript>)<Subscript>3</Subscript>

Ordered arrays of nanowires of the photochromic antiferromagnet SpFeMn(C₂O₄)₃ (where Sp is 1-{(1′,3′,3′-trimethyl-6-nitro-5′-chlorospiro[2H-1-benzopyran-2,2′-indolin]-8-yl)methyl}pyridinium) have been fabricated in anodized aluminum oxide pores with diameters of 20 and 200 nm. It has been revealed that the growth of the spin-glass phase with noncollinear ordering of spins in nanowires is suppressed in favor of the uniaxial antiferromagnetic phase. A decrease in the nanowire diameter leads to an increase in the anisotropy of the magnetic resonance spectra. This is associated with the magnetocrystalline anisotropy that considerably exceeds the anisotropy of the nanowire shape.     

Effect of change in structural and magnetic states of Pt<Subscript>74.1</Subscript>Fe<Subscript>25.9</Subscript> alloy on its optical properties

The effect of atomic disordering on the optical properties of Pt_74.1Fe_25.9 alloy, whose stoichiometry is close to that of Pt₃Fe, has been investigated. The optical constants of ordered and plastically deformed alloys, which are, respectively, in the paramagnetic and ferromagnetic states, have been measured by the polarimetric method. The frequency dispersions of the permittivity, optical conductivity, and reflectivity, as well as the microscopic characteristics of conduction electrons (plasma and relaxation frequencies), have been calculated. The energy dependences of the optical conductivity are compared to the calculated energy-band structure of atomically ordered and disordered Pt₃Fe compounds.     

Effect of severe plastic deformation and ultrarapid quenching on the properties of magnetic shape memory alloys near the Ni<Subscript>2</Subscript>MnGa composition

The effect of ultrarapid quenching from melt and subsequent severe plastic deformation by torsion in Bridgman anvils on the temperatures of martensitic (T _M) and magnetic (T _C ) phase transitions in magnetic shape memory alloys has been investigated. The features of the crystal structure and magnetic, electric, and optical properties of Ni₂MnGa-based alloys with different degrees of structural ordering are discussed. The effect of doping with copper and cobalt on the properties of nonstoichiometric Ni₅₀Mn_28.5Ga_21.5 alloy is considered.     

Spin fluctuations in the stacked-triangular antiferromagnet YMnO<Subscript>3</Subscript>

The spectrum of spin fluctuations in the stacked-triangular antiferromagnet YMnO₃ was studied above the Néel temperature using both unpolarized and polarized inelastic neutron scattering. We find an in-plane and an out-of-plane excitation. The in-plane mode has two components just above T _N : a resolution-limited central peak and a Debye-like contribution. The quasi-elastic fluctuations have a line width that increases with q as Dq ^z and the dynamical exponent z = 2.3. The out-of-plane fluctuations have a gap at the magnetic zone center and do not show any appreciable q dependence at small wave vectors.     

NMR spectrum in a Mn<Subscript>3</Subscript>Al<Subscript>2</Subscript>Ge<Subscript>3</Subscript>O<Subscript>12</Subscript> noncollinear antiferromagnet

The dependence of the NMR frequencies on the external magnetic field in a Mn₃Al₂Ge₃O₁₂ non-collinear 12-sublattice antiferromgnet is calculated using the exchange approximation for the spin dynamics.     

Magnetic resonance of the RbMnBr<Subscript>3</Subscript> antiferromagnet under pressure

The antiferromagnetic resonance spectrum was experimentally studied for a noncollinear RbMnBr₃ antiferromagnet under a mechanical pressure applied to the sample in various directions. It is shown that the incommensurate magnetic phase existing in the initial system in the presence of regular crystallographic distortions is sensitive to the pressure applied along one of the sample axes. The critical transition field to the commensurate phase decreased under pressure. It was also found that the pressure influences the uniaxial anisotropy appearing in the crystal basal plane in the presence of orthorhombic distortions. These effects were analyzed with allowance for the domain structure of the sample.     

Magnetic properties of DyFe<Subscript>3</Subscript>(BO<Subscript>3</Subscript>)<Subscript>4</Subscript>

The magnetic properties of an easy-axis trigonal DyFe₃(BO₃)₄ antiferromagnetic crystal have been theoretically studied. On this basis, recent experimental data [1] on the field and temperature dependences of magnetization and the temperature dependence of the initial magnetic susceptibility for three crystallographic directions in this antiferromagnet have been interpreted. The characteristics of the trigonal crystal field for the rare earth ion and the parameters of the Fe-Fe and Fe-Dy exchange interactions are determined. Limitations imposed by features of the magnetic characteristics (anisotropic magnetization in the three crystallographic directions, Schottky-type anomalies in the magnetic susceptibility, etc.) on the possible splitting of the ground-state multiplet in the crystal field and the splitting of the lowest doublet due to the f-d interaction for Dy³⁺ ions are established.     

Entanglement in the linear-chain Heisenberg antiferromagnet Cu(C<Subscript>4</Subscript>H<Subscript>4</Subscript>N<Subscript>2</Subscript>)(NO<Subscript>3</Subscript>)<Subscript>2</Subscript>

Quantum correlations are generally impossible to address directly in bulk systems. Quantum measures extended only to a few number of parties can be discussed in practice. In the present work we study a cluster of spins belonging to a compound whose structure is that of a quantum magnet. We reproduce at a much smaller scale the experimental outcomes and then we study the role of quantum correlations there. A macroscopic entanglement witness has been introduced in order to reveal quantum correlations at nonzero temperatures. The critical point beyond which entanglement is zero is found at T _c = 15 K.     

Effect of an interface boundary on the magnetooptical and magnetotransport properties of La<Subscript>0.67</Subscript>Ca<Subscript>0.33</Subscript>MnO<Subscript>3</Subscript>/La<Subscript>0.67</Subscript>Sr<Subscript>0.33</Subscript>MnO<Subscript>3</Subscript> heterostructures

The optical, magnetooptical (Kerr effect and magnetotransmission), and magnetotransport properties of La_2/3Ca_1/3MnO₃/La_2/3Sr_1/3MnO₃ and La_2/3Ca_1/3MnO₃/SrTiO₃/La_2/3Sr_1/3MnO₃ heterostructures on SrTiO₃ substrates are studied. The contribution of the interface boundary to the magnetotransmission is typical of a material with a transitional composition. It is found that a 2-nm-thick SrTiO₃ spacer does not influence the shape and position of the magnetotransmission peak in a field normal to the surface of the heterostructure but increases the contribution of the upper layer to the magnetotransmission in the Voigt geometry and also enhances the magnetoresistance that is due to the tunneling of spin-polarized carriers through the spacer. The Kerr spectra taken of the heterostructures are typical of single-layer single-crystal films.     

Preparation and properties of Fe and Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> nanoparticles in ZrO<Subscript>2</Subscript> matrix

Iron and magnetite nanoparticles in zirconium oxide matrix have been prepared by a heat treatment of a mixture of nanocrystalline iron oxide and zirconium oxide or zirconium hydride powders. Changes in the phase composition of the as-mixed powders during annealing in vacuum or in hydrogen were monitored using thermomagnetic curves. Structure and phase composition of the final products were characterized by X-ray powder diffraction and ⁵⁷Fe Mössbauer spectroscopy. Influence of the composition of the original mixture and quality of the annealing atmosphere on the final properties of the composites are discussed.     

Optical spectra of nanoceramics of yttrium-iron garnet Y<Subscript>3</Subscript>Fe<Subscript>5</Subscript>O<Subscript>12</Subscript> obtained by the method of intense plastic deformation

The features of the optical properties of nanostructured samples of iron-yttrium garnet Y₃Fe₅O₁₂ (YIG) in the range of 0.5 to 4.7 eV, which includes both the fundamental-absorption region and low-energy electron excitations, have been investigated by spectroscopic ellipsometry. The results are discussed in comparison with the measurement data of a YIG single crystal. The dispersion of the optical functions in nanostructured samples is significantly different from that for the single crystal: the spectral density is redistributed from the energy region above the fundamental absorption edge to the region below the edge. It has been shown that the energy positions of the main electronic transitions in nanostructured samples are on the whole the same as in the single crystal; at the same time, the intensity of low-energy transitions increases. The possible causes of this increase and the resolution of the fine absorption structure in the bandgap of nanostructured Y₃Fe₅O₁₂ are discussed.     

Magnetic properties of the quasi-two-dimensional crystal (CH<Subscript>3</Subscript>NH<Subscript>3</Subscript>)<Subscript>2</Subscript>CuBr<Subscript>4</Subscript>

The magnetic properties of (CH₃NH₃)₂CuBr₄ quasi-two-dimensional crystals were studied experimentally. The magnetic-field and temperature dependences of magnetization were measured for various magnetic field orientations relative to the crystallographic axes. Possible reasons for features in the behavior of the magnetization are discussed.