N. I. Kourov

Electronic properties of strain-disordered Ni2.16Mn0.84Ga alloy

The effect of ultrarapid quenching from the melt and severe plastic torsional deformation under high pressure on the crystalline structure and the electrical, optical, and magnetic properties of a Ni2.16Mn0.84Ga alloy was studied. The electrical properties are discussed in terms of the Mott two-band model. The peculiarities of the magnetic properties are associated with the magnetism of itinerant electrons. The optical properties correlate with the variations in the electronic spectrum upon disordering of the alloy that follow from the results of the available energy-band-structure calculations.

Thermal expansion of ScxTi1−xFe2 itinerant magnets

A study of the thermal expansion coefficient (TEC) of the ScxTi1−xFe2 itinerant magnets has been made within the 5–1200 K range at the transition from the TiFe2 antiferromagnet (TN=270 K) to the ScFe2 ferromagnet (TC=540 K). A negative TEC magnetic contribution αm(T) has been found, which is associated with the formation of spin-fluctuation-induced local magnetic moments in both the magnetically ordered and the paramagnetic state. The specific features in the αm(T) dependence are shown to be due to the shape of the density-of-states function near the Fermi level.

Features of properties of microinhomogeneous PdMn x Fe1− x alloys

Complex investigation of the properties of PdMnxFe1− x ternary alloys with interacting magnetic and structural order parameters has been performed. It is shown that the complex structural and magnetic state near the transition from the atomically ordered PdFe ferromagnet to the intermetallic antiferromagnetic PdMn compound leads to unusual features not only in magnetic and lattice characteristics but also in electronic properties.

Geometric resonance in the optical properties of microinhomogeneous PdMnxFe1−x alloys

The optical properties of PdMnxFe1−x ternary alloys in the homogeneous ferromagnetic (F1, for x ∼ 0) and antiferromagnetic (A, for x ∼ 1) states, as well as in the microinhomogeneous state (at x=0.7), are discussed. In the x=0.7 alloy, the presence of nuclei of the low-resistivity, PdFe-type F1 phase in the high-resistivity, PdMn-type A matrix was shown to produce a narrow maximum on the optical-conductivity σ(ω) curve at E ∼ 0.1 eV, which is due to a geometric resonance associated with light scattering from phase inhomogeneities of the sample. The behavior of σ(ω) in the interband transition region is dominated by parameters of the electronic spectrum of both the A and F1 phases.

Electrical resistivity of microinhomogeneous PdMnxFe1−x alloys

The electronic band-structure calculations of the PdFe ferromagnet and the PdMn antiferromagnet performed in this work permit one to conclude that the specific features of the electrical resistivity observed in the ternary PdMnxFe1−x alloy system [the deviation from the Nordheim-Kurnakov rule ρ0(x)∼x(1−x), which is accompanied by a high maximum of residual resistivity (not typical of metals) ρ0m∼220 µΩ cm at xC∼0.8 and a negative temperature resistivity coefficient in the interval 0.5≤x≤1] are due to the microinhomogeneous (multiphase) state of the alloys and a variation in the band-gap parameter d spectrum caused by antiferromagnetic ordering of a PdMn-type phase.

Natural ferromagnetic resonance in the disordered alloy Pd2AuFe

A contribution to electromagnetic power losses, additional to the losses due to eddy currents and exhibiting a resonance frequency dependence with the main maximum near 1 GHz, has been observed for the ferromagnetic alloy Pd2AuFe in the frequency range 0.9 MHz–10 GHz in the absence of an external constant magnetic field. Investigations performed in a dc magnetic field show that this effect is a natural ferromagnetic resonance due to intradomain magnetization precession in the effective magnetic-anisotropy field.

Low-frequency optical conductivity of inhomogeneous alloys

The optical conductivity of PdMn0.7Fe0.3, Pd2AuFe, and GdCu alloys with different degrees of homogeneity has been measured. Possible reasons for a low-frequency (E < 1 eV) anomalous maximum in the σ(ω) curves are discussed. The deviation from the Drude behavior of σ(ω) is assigned to the presence of small “metallic” inclusions in the high-resistivity matrix of these alloys.

Low-temperature heat capacity of microscopically inhomogeneous PdMn x Fe1 − x alloys

The low-temperature (1.8 ≤ T ≤ 30 K) heat capacity of microscopically inhomogeneous PdMnxFe1 − x alloys in the region of the transition between the ferromagnetic, atomically ordered state of the PdFe alloy and the antiferromagnetic intermetallic state of the PdMn compound was studied. Theoretical calculations of the electronic band structure were found to agree with experimental data on the low-temperature heat capacity of the alloys. Possible reasons for the anomalous behavior of the electronic properties (electrical resistivity, ordinary Hall effect, thermopower, electronic heat capacity) at nucleation of the low-Ohmic (ρ0 < 8 μΩ cm) PdFe-type phase in the high-Ohmic (ρ0 < 100 μΩ cm) PdMn-type matrix at xC2 ∼ 0.8 are discussed.

Hall effect in microscopically inhomogeneous magnetic alloys

A theory of the generalized conductivity for the normal component of the Hall effect is developed. It is shown that the normal Hall effect coefficient R0 of microscopically inhomogeneous magnetic alloys GdZnxCu1−x, which at low temperatures consist of ferro-, antiferro-, and paramagnetic phases, can be described satisfactorily on the basis of an effective-medium theory. The experimentally observed relationship between the coefficient R0(x) and the resistivity ρ(x) is obtained.

Magnetic susceptibility and inelastic electrical resistivity of GdZnxCu1−x alloys

The deviation from the Nordheim-Kurnakov rule and the anomalous behavior of spin-disordered electrical resistivity in quasi-binary GdZn (TC=268 K)-GdCu (TN=142 K) solid solutions is explained in effective medium approximation within percolation theory for the case of three phases, viz., ferro-, antiferro-, and paramagnetic. The strong increase of ρ at zinc concentrations x∼0.45 is attributed to the closeness of the system to the percolation threshold. The phase volumes calculated for the random-distribution case fit well to the concentration dependence of magnetic susceptibility.