arXiv subjects

K. V. Zakharov

Publications and source records attributed to K. V. Zakharov.

4 recordsLinked to original sources

arXiv2026

Collinear and noncollinear antiferromagnetic ordering in a highly frustrated decorated square kagomé lattice antiferromagnets of the nabokoite family

Nabokoite family compounds ACu$_7$(TeO$_4$)(SO4)$_5$X (A=Na, K, Rb, Cs; X=Cl, Br) host frustrated 2D square kagom'{e} lattice layers decorated by additional inter-layer magnetic ions. We study magnetic order in nabokoites with multi-frequency electron spin resonance spectroscopy and thermodynamic measurement (specific heat, magnetization and dielectric permittivity). Our study reveals that the choice of the low-temperature ground state is qualitatively different in light-alkali-ion (K, Na) and heavy-alkali-ion (Rb, Cs) compounds. Heavy-alkali-ion nabokoites order in conventional collinear antiferromagnetic pattern with easy-axis anisotropy. The parameters of the ordered antiferromagnetic state are very close for all heavy-alkali-ion subfamily. Light-alkali-ion members of nabokoite family demonstrate much more complicated route to the ordered state: firstly, a ferroelectric transition at 25-90K lifts the frustration and thus pre-cooks the low-temperature ordering; secondly, an unusual noncollinear magnetic order develops via two-step phase transition with first transition temperature $T_{c1}\simeq 5-6$K and the second transition at $T_{c2}\simeq 3-4$K. Noncollinear order is evidenced by observation of characteristic non-Larmor antiferromagnetic resonance mode. Spin dynamics of light-alkali-ion nabokoites is characterized by three zero-field magnon gaps and two spin-reorientation fields, the values of magnon gaps and critical fields are quite different for different compounds. The finite-size cluster modeling of pyramidal structural block of nabokoite structure combined suggests that the critical closeness of the nabokoite exchange coupling parameters to the border-line between the different quantum ground state of pyramidal building block of nabokoite structure could be the clue to the choice of qualitatively different ordered state in light- and heavy-alkali-ion nabokoites.

cond-mat.str-el↗

arXiv2023

Static and resonant properties of decorated square kagome lattice compound KCu$_7$(TeO$_4$)(SO$_4$)$_5$Cl

The magnetic subsystem of nabokoite, KCu$_7$(TeO$_4$)(SO$_4$)$_5$Cl, is constituted by copper ions forming a buckled square kagomé lattice decorated by quasi-isolated ions. This combination determines peculiar physical properties of this compound evidenced in electron spin resonance (ESR) spectroscopy, dielectric permittivity $\varepsilon$, magnetization $M$ and specific heat $C_p$ measurements. At lowering temperature, the magnetic susceptibility $χ= M/H$ passes through a broad hump inherent for low-dimensional magnetic systems at about 150 K and a sharp peak at antiferromagnetic phase transition at $T_N = 3.2 $K. The $C_p(T,H)$ curves demonstrate additional peak-like anomaly at $T_{peak}= 5.7$K robust to magnetic field. The latter can be ascribed to low-lying singlet excitations filling the singlet-triplet gap in magnetic excitation spectrum of the square kagomé lattice [J.Richter, O.Derzhko and J.Schnack, Phys. Rev. B \textbf{105} (2022) 144427]. ESR spectroscopy provides indications that antiferromagnetic structure below $T_N$ is non-collinear. Separate issue is the observation of antiferroelectric-type behavior in $\varepsilon$ at low temperatures, which tentatively reduces the symmetry and partially lifts frustration of magnetic interactions of decorating copper ions with buckled square kagomé lattice. These complex thermodynamic and resonant properties signal the presence of two weakly coupled magnetic subsystems in nabokoite, namely a spin-liquid in square kagomé lattice layers and an antiferromagnet represented by decorating ions.

cond-mat.str-el↗

arXiv2020

Hidden Magnetic Order in Triangular-Lattice Magnet Li2MnTeO6

The manganese tellurate Li2MnTeO6 consists of trigonal spin lattices made up of Mn4+ (d3, S = 3/2) ions. The magnetic properties of this compound were characterized by several experimental techniques, which include magnetic susceptibility, specific heat, dielectric permittivity, electron spin resonance (ESR), nuclear magnetic resonance (NMR) and neutron powder diffraction (NPD) measurements, and by density functional calculations (DFT). The magnetic susceptibility chi(T) demonstrates very unusual behavior. It isdescribed by the Curie-Weiss law at high temperature with Curie-Weiss temperature of Theta = -74 K, exhibits no obvious anomaly indicative of a long-range magnetic ordering at low magnetic fields. At high magnetic fields, however, the character of chi(T) changes showing a maximum at about 9 K. That this maximum of chi(T) reflects the onset of an antiferromagnetic order was confirmed by specific heat measurements, which exhibit a clear lambda-type anomaly at TN around 8.5 K even at zero magnetic field, and by 7Li NMR and dielectric permittivity measurements. The magnetic structure of Li2MnTeO6, determined by neutron powder diffraction measurements at 1.6 K, is described by the 120-degree non-collinear spin structure with the propagation vector k = (1/3, 1/3, 0). Consistent with this finding, the spin exchange interactions evaluated for Li2MnTeO6 by density functional calculations are dominated by the nearest-neighbor antiferromagnetic exchange within each triangular spin lattice. This spin lattice is strongly spin frustrated with f = |Theta|/TN around 8 and exhibits a two-dimensional magnetic character in a broad temperature range above TN.

cond-mat.mtrl-sci↗

arXiv2017

Spin-order-induced multiferroicity in LiCuFe2(VO4)3 and disorder effects in NaCuFe2(VO4)3

Mixed spin chain compounds, ACuFe2(VO4)3 (A= Li,Na), reach magnetically ordered state at TN ~ 11 K (Li) or ~ 9 K (Na) and experience further transformation of magnetic order at T* ~ 7 K (Li) or ~ 5 K (Na), evidenced in magnetic susceptibility chi and specific heat Cp measurements. While no anomaly has been detected in dielectric property of NaCuFe2(VO4)3, the step-like feature precedes a sharp peak in permittivity epsilon at TN in LiCuFe2(VO4)3. These data suggest the spin-order-induced ferroelectricity in Li compound and no such thing in Na compound. On the contrary, the Moessbauer spectroscopy study suggests similarly wide distribution of hyperfine field in between T* and TN for both the compounds. The first principles calculations also provide similar values for magnetic exchange interaction parameters in both compounds. These observations lead us to conclude on the crucial role of alkali metals mobility within the channels of the crystal structure needed to be considered in explaining the improper multiferroicity in one compound and its absence in other.

cond-mat.mtrl-sci↗