arXiv subjects

V. Yu. Irkhin

Publications and source records attributed to V. Yu. Irkhin.

At least 19 recordsLinked to original sources

arXiv2026

Quantum magnetic phase transitions in a Kugel-Khomskii model including spin-orbit coupling

Using the formalism of pseudospin and isospin operators the Hamiltonian of an effective Kugel-Khomskii model with spin-orbit coupling is derived with an exact account of the $t_{2g}$ multiplet splitting by the crystal field. An analytical solution is obtained for an arbitrary relation between the Hubbard repulsion and crystal field splitting, i.e., interpolating the cases of Mott-Hubbard and charge-transfer insulators. A description of orbital orders is given in terms of octupole moments. The ground-state phase diagram is constructed in the parameter space spanned by spin-orbit coupling, Hund's exchange, and Hubbard interaction. We investigate a quantum phase transition between a state exhibiting hidden magnetic and orbital long-range order and a ferromagnetic state with a reduced magnetic moment accompanied by antiferroorbital order. It is shown that the cooperative effect of Hund's and spin-orbit interactions gives rise to an easy-plane-type anisotropy.

cond-mat.str-el↗

arXiv2026

Monte Carlo study of the classical antiferromagnetic $J_1$-$J_2$-$J_3$ Heisenberg model on a simple cubic lattice

An extensive Monte Carlo study of the classical Heisenberg model on a simple cubic lattice with antiferromagnetic exchange interactions $J_n$ between the first, second, and third neighbors is performed in a broad region of $J_2 / J_1$, $J_3 / J_1$ ratios, and temperature. The character of the phase transitions is analyzed via the Binder cumulant method. The Neel temperature $T_{\mathrm{N}}$ and the frustration parameter (the ratio $f= |\theta|/T_{\mathrm{N}}$, $\theta$ being the Curie-Weiss temperature) are calculated. A comparison with the Tyablikov approximation is carried out. The strength of the frustration effects is explored. Possible applications to antiferromagnetic perovskites, such as CaMnO$_3$ and HgMnO$_3$, are discussed.

cond-mat.str-el↗

arXiv2025

Features of the Electronic and Magnetic Properties of Heusler Alloys in the States of a Half-Metallic Ferromagnet and a Spin-Gapless Semiconductor

The review treats Heusler alloys that display distinctive functional properties, including shape-memory behavior and magnetocaloric effects. Particular emphasis is placed on Heusler systems in which half-metallic ferromagnetism and spin-gapless semiconductor state are realized. Although these compounds are crystallographically rather "ordinary", peculiarities of their electronic structure and magnetic state lead to unconventional kinetic and magnetic properties. Their magnetic and transport characteristics are highly sensitive to external stimuli, and changes in alloy composition or external parameters can induce transitions between the states considered. This tunability provides further opportunities for controlling the electronic and magnetic properties of Heusler alloys and for exploiting them in applications such as spintronics and micro- and nanoelectronics.

cond-mat.mtrl-sci↗

arXiv2025

Low-dimensional Heisenberg magnets: Riemann zeta function regularization

The Riemann zeta function regularization is employed to extract finite temperature corrections to effective magnetic moment $S^*$ of one- and two-dimensional Heisenberg ferro- and antiferromagnets. Whereas for the one-dimensional ferromagnet we obtain the usual $T^{1/2}$ spin-wave dependence, for the antiferromagnetic chain the dependence is described by a generalized incomplete Riemann function. The quantity $S^*$ determines strong short-range magnetic order in the absence of long-range order, in particular the correlation length. For the one-dimensional ferromagnet, the results are confirmed by the self-consistent spin-wave theory and Monte Carlo simulations by Takahashi et al.

cond-mat.str-el↗

arXiv2025

Highly correlated electronic state in a ferrimagnetic quadruple perovskite CuCu$_3$Fe$_2$Re$_2$O$_{12}$

Recently synthesized quadruple perovskite CuCu$_3$Fe$_2$Re$_2$O$_{12}$ possesses strong ferromagnetism and unusual electron properties, including enhanced electronic specific heat. Application of the first principles electronic structure approaches unambiguously shows importance of the many-body effects in this compound. While CuCu$_3$Fe$_2$Re$_2$O$_{12}$ is half-metallic ferrimagnet in the DFT+U method, in the density functional theory (DFT) combined with the dynamical mean-field theory (DMFT) it appears to be a metal. Strong correlations lead to a renormalization of electronic spectrum and formation of incoherent states close to the Fermi level. Electronic specific heat and magnetic properties obtained in the DFT+DMFT approach are in better agreement with available experimental data than derived by other band structure techniques.

cond-mat.str-el↗

arXiv2025

Sophomore's dream function: asymptotics, complex plane behavior and relation to the error function

Sophomore's dream sum $S=\sum_{n=1}^\infty n^{-n}$ is extended to the function $f(t,a)=t\int_{0}^{1}(ax)^{-tx}dx$ with $f(1,1)=S$. Asymptotic behavior for a large $|t|$ is obtained, which is exponential for $t>0$ and $t<0,a>1$, and inverse-logarithmic for $t<0,a<1$. An advanced approximation includes a half-derivative of the exponent and is expressed in terms of the error function. This approach provides excellent interpolation description in the complex plane. The function $f(t,a)$ demonstrates for $a>1$ oscillating behavior along the imaginary axis with slowly increasing amplitude and the period of $2\pi iea$, modulation by high-frequency oscillations being present. Also, $f(t,a)$ has non-trivial zeros in the left complex half-plane with Im$t_n \simeq 2(n-1/8)\pi e/a$ for $a \geq 1$. The results obtained describe analytical integration of the function $x^{tx}$.

math.CA↗

arXiv2024

Itinerant electron metamagnetism for lattices with van Hove density-of-states singularities near the Fermi level

Itinerant-electron metamagnetism is investigated within the Hubbard model for various lattices having van Hove singularities (vHS) in the electronic spectrum: face-centered cubic and orthorhombic lattices. The remarkable itinerant-electron metamagnetic transition occurs provided that the Fermi level is in the region with a strong positive curvature of the density of electron states typically positioned between two close van Hove singularities. Orthorhombic distortion of a~tetragonal lattice is a promising mechanism for generating two closely split vHS with strong density-of-states curvature between them. A phase diagram in terms of electron filling and Hubbard interaction parameter is presented, which shows the paramagnetic-metamagnetic-ferromagnetic phase transition and regions of saturated and non-saturated magnetism. The standard Landau theory expansion based on~the~electron density of states in the vicinity of the Fermi level is demonstrated to be insufficient to describe the whole magnetic phase diagram including the itinerant-electron metamagnetic transition.

cond-mat.str-el↗

arXiv2024

Regularities and features in the behavior of electrical and magnetic properties of Co$_2$FeZ (Z = Al, Si, Ga, Ge, Sn, Sb) half-metallic ferromagnetic Heusler alloys

The electrical resistivity, magnetization, and Hall effect in Co$_2$FeZ (Z = Al, Si, Ga, Ge, Sn, Sb) ferromagnetic Heusler alloys are studied. A number of correlations between the electronic and magnetic characteristics of the studied alloys are revealed while the atomic number of the Z-component changes. For the Co$_2$FeAl and Co$_2$FeSi half-metallic ferromagnets, the magnitude of magnetization is consistent with the Slater-Pauling rule. For the Co$_2$FeAl, Co$_2$FeSi, and Co$_2$FeGe compounds, a quadratic temperature dependence of electrical resistivity at temperatures below 30 K and above 65 K is found. At the same time, in the region of intermediate temperatures (from 40 K to 65 K), a power-law dependence of $T^b$ with an exponent of 3.5 < b < 4 is observed, which may be due to two-magnon scattering processes.

cond-mat.mtrl-sci↗

arXiv2024

Rattling Phonon Modes in Quadruple Perovskites

Rattling phonon modes are known to be origin of various anomalous physical properties such as superconductivity, suppression of thermal conductivity, enhancement of specific heat etc. By means of DFT+$U$ calculations we directly show presence of the rattling mode in the quadruple perovskites CuCu$_3$V$_4$O$_{12}$ and CuCu$_3$Fe$_2$Re$_2$O$_{12}$ and argue that this can develop in others as well. It is demonstrated that Cu ions at $A$ sites vibrate in the center of the icosahedral oxygen O$_{12}$ cages and the corresponding potential has a complicated form with many local minima.

cond-mat.str-el↗

arXiv2023

Magnetic States and Electronic Properties of Manganese-Based Intermetallic Compounds Mn$_2$YAl and Mn$_3$Z (Y = V, Cr, Fe, Co, Ni; Z = Al, Ge, Sn, Si, Pt)

We present a brief review of experimental and theoretical papers on studies of electron transport and magnetic properties in manganese-based compounds Mn$_2$YZ and Mn$_3$Z (Y = V, Cr, Fe, Co, Ni, etc.; Z = Al, Ge, Sn, Si, Pt, etc.). It has been shown that in the electronic subsystem of Mn$_2$YZ compounds, the states of a half-metallic ferromagnet and a spin gapless semiconductor can arise with the realization of various magnetic states, such as a ferromagnet, a compensated ferrimagnet, and a frustrated antiferromagnet. Binary compounds Mn$_3$Z have the properties of a half-metallic ferromagnet and a topological semimetal with a large anomalous Hall effect, spin Hall effect, spin Nernst effect, and thermal Hall effect. Their magnetic states are also very diverse: from a ferrimagnet and an antiferromagnet to a compensated ferrimagnet and a frustrated antiferromagnet, as well as an antiferromagnet with a kagome-type lattice. It has been demonstrated that the electronic and magnetic properties of such materials are very sensitive to external influences (temperature, magnetic field, external pressure), as well as the processing method (cast, rapidly quenched, nanostructured, etc.). Knowledge of the regularities in the behavior of the electronic and magnetic characteristics of Mn$_2$YAl and Mn$_3$Z compounds can be used for applications in micro- and nanoelectronics and spintronics.

cond-mat.mtrl-sci↗

arXiv2023

Magnetism, non-Fermi-liquid behavior and deconfinement in Kondo lattices

A formulation of the effective hybridization model is developed which describes Fermi-liquid Kondo and fractionalized Fermi-liquid (deconfinement spin-liquid-like) states with account of possible magnetic ordering. A unified consideration of charge and magnetic fluctuation is performed within perturbation theory in hybridization and within gauge field treatment. The corresponding contributions to specific heat and resistivity are compared.

cond-mat.str-el↗

arXiv2023

Magnetic order and electronic transport properties in the Mn$_3$Al compound: the role of the structural state

Electronic transport and magnetic properties of bulk and rapid melt quenched samples of the Mn$_3$Al Heusler alloy were studied. A correlation between the magnetic and structural states was established. For a cast sample, there is no ferromagnetic moment, and the behavior of the magnetic susceptibility (break at low temperatures and the Curie-Weiss law with high values of the paramagnetic Curie temperature) indicates a frustrated antiferromagnetic state. At the same time, for a rapid melt quenched sample, a ferrimagnetic state is observed with a moment close to compensation. The results of measurements of the electrical resistivity and the Hall effect evidence as well in favor of the implementation of these magnetic states.

cond-mat.str-el↗

arXiv2023

Hubbard bands, Mott transition and deconfinement in strongly correlated systems

The problem of deconfinement phases in strongly correlated systems is discussed. In space-time dimension $d=3+1$, a competition of confinement and Coulomb phases occurs, but in $d=2+1$ the confining phase dominates owing to monopole proliferation, but gapless fermion excitations can change the situation. Combining the Kotliar-Ruckenstein representation and fractionalized spin-liquid deconfinement picture, the Mott transition and Hubbard subbands are treated, general expressions in the case of an arbitrary bare band spectrum being obtained. The transition into a metallic state is determined by condensation of a gapless boson mode. The spectrum picture in the insulating state is considerably influenced by the spinon spin-liquid spectrum and hidden Fermi surface.

cond-mat.str-el↗

arXiv2022

S. Vonsovsky and the dawn of the theory of strongly correlated systems

A survey of scientific and social activity of S. V. Vonsovsky is presented. His fundamental works on the theory of electronic properties and magnetism of transition and rare-earth metals and their compounds are reviewed. The historical development of the many-electron polar (preceding the famous Hubbard model) and $s-d(f)$ exchange (''Vonsovsky-Zener'', ''Kondo lattice'') models is considered.

cond-mat.str-el↗

arXiv2022

Topological states in strongly correlated systems

Topological order in strongly correlated systems, including quantum spin liquids, quantum Hall states in lattices and topological superconductivity is treated. Various metallic non-Fermi-liquid states are discussed, including fractionalized Fermi-liquid (FL$^*$) and phase string theories. Classification of topological states and differences between quantum and classical topology are considered.

cond-mat.str-el↗

arXiv2022

Unusual kinetic properties of usual Heusler alloys

The review considers various groups of Heusler compounds, which can have the properties of a semiconductor, a half-metallic ferromagnet, a spin gapless semiconductor, a topological semimetal, and a noncollinear antiferromagnet. In these Heusler compounds, "conventional" from the point of view of the crystal structure, unusual kinetic and magnetic properties can be observed, which are caused by the features of their electronic structure (e.g., presence of an energy gap for one spin projection) and magnetic state (e.g., strong ferromagnetism, compensated ferrimagnetism, etc.). Their magnetic and kinetic characteristics are very sensitive to external influences. Depending on the alloy composition and external parameters, transitions between the considered states can be realized. All this opens up further prospects for controlling the electronic and magnetic characteristics of such compounds and their practical application.

cond-mat.mtrl-sci↗

arXiv2022

Relations between $e$ and $\pi$: Nilakantha's series and Stirling's formula

Approximate relations between $e$ and $\pi$ are reviewed, some new connections being established. Nilakantha's series expansion for $\pi$ is transformed to accelerate its convergence. Its comparison with the standard inverse-factorial expansion for $e$ is performed to demonstrate similarity in several first terms. This comparison clarifies the origin of the approximate coincidence $e+2\pi \approx 9$. Using Stirling's series enables us to illustrate the relations $\pi^4+\pi^5 \approx e^6$ and $\pi^{9}/e^{8} \approx 10$.The role of Archimede's approximation $\pi=22/7$ is discussed.

math.HO↗

arXiv2022

Giant density-of-states van Hove singularities in the face-centered cubic lattice

All van Hove singularities in the density of states (DOS) of face-centered cubic lattice in the nearest and next-nearest neighbour approximation, focusing on higher-order ones, are found and classified. At special values of the ratio $τ$ of nearest and next-nearest neighbour hopping integrals, $t$ and $t'$, giant DOS singularities, caused by van Hove lines or surfaces, are formed. An exact formula for DOS which provides efficient numerical implementation is proposed. The standard tetrahedron method is demonstrated to be inapplicable due to its poor convergence in the vicinity of kinks caused by van Hove singularities. A comparison with the case of large space dimensionality (infinite coordination number) including next-nearest neighbours is performed.

cond-mat.str-el↗