arXiv subjects

A. Lynnyk

Publications and source records attributed to A. Lynnyk.

4 recordsLinked to original sources

arXiv2025

NMR evidence for an antisite-induced magnetic moment on Bi in a topological insulator heterostructure MnBi$_2$Te$_4$/(Bi$_2$Te$_3$)$_n$

MnBi$_2$Te$_4$ (MBT) is the first intrinsic magnetic topological insulator, combining a topologically protected surface metallic state and intrinsic magnetic order. A structural compatibility with the nonmagnetic Bi$_2$Te$_3$ (BT) parent compound gives a possibility to create MBT/BT heterostructures and manipulate their magnetic state in view of optimizing the Quantum Anomalous Hall Effect (QAHE). In this work an extensive Nuclear Magnetic Resonance (NMR) study, supported by the bulk magnetization measurements has been performed at 4.2 K on a self-organized single crystal MnBi$_2$Te$_4$/(Bi$_2$Te$_3$)$_n$ heterostructure, obtained from the Mn$_{0.81}$Bi$_{2.06}$Te$_{4.13}$ melt. $^{55}$Mn and $^{209}$Bi NMR signals have been recorded as a function of the out-of-plane magnetic field up to 6 T, covering a spin-flop transition (SFT) from the antiferromagnetic (AFM) to the canted antiferromagnetic (CAFM) configuration of the Mn layers. The canting angle at different external field values has been estimated based on NMR data. Presence of the AFM-coupled Mn antisites has been evidenced and shown to induce an antiparallel magnetic moment on Bi atoms within the host Bi layer. Detection of the induced magnetic moment on bismuth which contributes a new ferromagnetic (FM) component is of utmost importance for understanding the magnetic interactions in the MBT/BT system. These findings have potentially important implications for engineering the QAHE devices.

cond-mat.mtrl-sci↗

arXiv2024

Orbital-selective Mott phase and spin nematicity in Ni-substituted FeTe$_{0.65}$Se$_{0.35}$ single crystals

The normal state in iron chalcogenides is metallic but highly unusual, with orbital and spin degrees of freedom partially itinerant or localized depending on temperature, leading to many unusual features. In this work, we report on the observations of two of such features, the orbital selective Mott phase (OSMP) and spin nematicity, evidenced in magnetization and magnetotransport [resistivity, Hall effect, anisotropic magnetoresistance (AMR)] of Fe$_{1-y}$Ni$_y$Te$_{0.65}$Se$_{0.35}$ single crystals, with $0 < y < 0.21$. Substitution of Ni dopes crystals with electrons, what eliminates some of the hole pockets from Fermi level, leaving only one, originating from $d_{xy}$ orbital. This leads to electron-dominated conduction at low $T$ for $y \gtrsim 0.06$. However, at high temperatures, $T \gtrsim 125 ÷178$ K, the conduction reverses to hole-dominated. Anomalies in magnetization and resistivity are observed at temperatures which approach high-$T$ boundary of the electron-dominated region. Analysis of these effects suggests a link with the appearance of the $d_{z^2}$ hole pockets at X points of the Brillouin zone in the OSMP phase, facilitated by the localization of $d_{xy}$ orbital, as recently reported by angular resolved photoemission experiments ($\textit{J. Huang et al., Commun. Phys. 5, 29 (2022)}$). The low-$T$ AMR shows mixed 4-fold and 2-fold rotational symmetry of in-plane magnetocrystalline anisotropy, with the 4-fold term the largest at small $y$, and suppressed at intermediate $y$. These results are consistent with the mixed stripe/bicollinear magnetic correlations at small $y$, and suppression of stripe correlations at intermediate $y$, indicating development of spin nematicity with increasing Ni doping, which possibly contributes to the suppression of superconductivity.

cond-mat.supr-con↗

arXiv2022

Electronic properties of TaAs2 topological semimetal investigated by transport and ARPES

We have performed electron transport and ARPES measurements on single crystals of transition metal dipnictide TaAs2 cleaved along the ($\overline{2}$ 0 1) surface which has the lowest cleavage energy. A Fourier transform of the Shubnikov-de Haas oscillations shows four different peaks whose angular dependence was studied with respect to the angle between the magnetic field and the [$\overline{2}$ 0 1] direction. The results indicate the elliptical shape of the Fermi surface cross-sections. Additionally, a mobility spectrum analysis was carried out, which also reveals at least four types of carriers contributing to the conductance (two kinds of electrons and two kinds of holes). ARPES spectra were taken on freshly cleaved ($\overline{2}$ 0 1) surface and it was found that bulk states pockets at the constant energy surface are elliptical, which confirms the magnetotransport angle dependent studies. First-principles calculations support the interpretation of the experimental results. The theoretical calculations better reproduce the ARPES data if the theoretical Fermi level is increased, which is due to a small n-doping of the samples. This shifts the Fermi level closer to the Dirac point, allowing to investigate the physics of the Dirac and Weyl points, making this compound a platform for the investigation of the Dirac and Weyl points in three-dimensional materials.

cond-mat.other↗

arXiv2020

Features of magnetic and magnetoelectric properties, H-T phase diagram of GdCr3(BO3)4

Comprehensive studies of magnetic properties of GdCr3(BO3)4 single crystal have been carried out. The integrals of intrachain and interchain exchange interactions in the chromium subsystem have been determined and the strength of Cr-Gd exchange interaction has been estimated. The values of the exchange field and the effective magnetic anisotropy field of GdCr3(BO3)4 have been estimated. The electric polarization along the a axis in the longitudinal geometry of the experiment has been detected. Correlations between the electric polarization and the magnetization of the studied compound have been found. The spin-reorientation phase transition in the magnetically ordered state has been found. This transition exists for the external magnetic field applied along any crystallographic direction and the transition field depends weakly on the direction of the field. The nature of the spin-reorientation phase transition has been discussed. Magnetic phase diagram has been constructed and spin configurations for the low-field and high-field phases have been proposed.

cond-mat.str-el↗