Search Results (5)

Introducing magnetic dopants into topological insulators (TIs) provides a pathway to realizing novel quantum phenomena, including the quantum anomalous Hall effect (QAHE) and axionic states. One of the most commonly used $3d$ transition metal dopants is Mn, despite its known tendency to be highly mobile and to cause phase segregation. In this study, we present a detailed magnetotransport investigation of Mn-overdoped Bi₂Te₃ thin films using field-effect transistor architectures. Building on our previous structural investigations of these samples, we examine how high Mn content influences their electronic transport properties. From our earlier studies, we know that high Mn doping concentrations lead to the formation of secondary phases, which significantly alter weak antilocalization behavior and suppress topological surface transport. To probe the gate response of these doped films over extended areas, we fabricate field-effect transistor structures, and we observe uniform electrostatic control of conduction across the magnetic phase. Inspired by recent developments in intrinsic topological systems such as the MnTe-Bi₂Te₃ septuple-layer compounds, we explore the influence of embedded ferromagnetic chalcogenide inclusions as an alternative route to engineer magnetic topological states and potentially expand the operational temperature range of QAHE-enabled devices. Full article

This study reports the structural and magnetic properties of Mn-doped ${\mathrm{Bi}}_2{\mathrm{Te}}_3$ thin films grown by magnetron sputtering. The films exhibit a ferromagnetic response that depends on the Mn doping concentration, as revealed by X-ray magnetic circular dichroism measurements. At an Mn concentration of ∼6.0%, a magnetic moment of (3.48 ± 0.25) ${\mathsf{\mu }}_{\mathrm{B}}$/Mn was determined. Structural analysis indicated the presence of a secondary ${\mathrm{MnTe}}_x$ phase, which complicates the interpretation of the magnetic properties. Additionally, the incorporation of Mn ions within the van der Waals gap and substitutional doping on Bi sites contributes to the observed complex magnetic properties. Intriguingly, a decrease in magnetic moment per Mn was observed with increasing Mn concentration, which is consistent with the formation of the intrinsic magnetic topological insulator ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$. Full article

We investigated the magnetic properties of the antiferromagnetic (AFM) topological insulator MnBi${}_2$Te${}_4$ with a partial substitution of Mn atoms by non-magnetic elements (A${}^{\mathrm{IV}}$ = Ge, Pb, Sn). Samples with various element concentrations (10–80%) were studied using SQUID magnetometry. The results demonstrate that, for all substitutes the type of magnetic ordering remains AFM, while the Néel temperature (T${}_{\mathrm{N}}$) and spin-flop transition field (H${}_{\mathrm{SF}}$) decrease with an increasing A${}^{\mathrm{IV}}$ = Ge, Pb, Sn concentration. The rate of decrease varies among the elements, being highest for Pb, followed by Sn and Ge. This behavior is attributed to the combined effects of the magnetic dilution and lattice parameter increase on magnetic properties, most prominent in (Mn${}_{1-x}$Pb${}_x$)Bi${}_2$Te${}_4$. Besides this, the linear approximation of the experimental data of T${}_{\mathrm{N}}$ and H${}_{\mathrm{SF}}$ suggests higher magnetic parameters for pure MnBi${}_2$Te${}_4$ than observed experimentally, indicating the possibility of their non-monotonic variation at low concentrations and the potential for enhancing magnetic properties through doping MnBi${}_2$Te${}_4$ with small amounts of nonmagnetic impurities. Notably, the (Mn${}_{1-x}$Pb${}_x$)Bi${}_2$Te${}_4$ sample with 10% Pb substitution indeed exhibits increased magnetic parameters, which is also validated by local-probe analyses using ARPES. Our findings shed light on tailoring the magnetic behavior of MnBi${}_2$Te${}_4$-based materials, offering insights into the potential applications in device technologies. Full article

One of the approaches to manipulate MnBi${}_2$Te${}_4$ properties is the magnetic dilution, which inevitably affects the interplay of magnetism and band topology in the system. In this work, we carried out angle-resolved photoemission spectroscopy (ARPES) measurements and density functional theory (DFT) calculations for analysing changes in the electronic structure of Mn${}_{1-x}$Ge${}_x$Bi${}_2$Te${}_4$ that occur under parameter x variation. We consider two ways of Mn/Ge substitution: (i) bulk doping of the whole system; (ii) surface doping of the first septuple layer. For the case (i), the experimental results reveal a decrease in the value of the bulk band gap, which should be reversed by an increase when the Ge concentration reaches a certain value. Ab-initio calculations show that at Ge concentrations above 50%, there is an absence of the bulk band inversion of the Te $p_z$ and Bi $p_z$ contributions at the $\Gamma$-point with significant spatial redistribution of the states at the band gap edges into the bulk, suggesting topological phase transition in the system. For case (ii) of the vertical heterostructure Mn${}_{1-x}$Ge${}_x$Bi${}_2$Te${}_4$/MnBi${}_2$Te${}_4$, it was shown that an increase of Ge concentration in the first septuple layer leads to effective modulation of the Dirac gap in the absence of significant topological surface states of spatial redistribution. The results obtained indicate that surface doping compares favorably compared to bulk doping as a method for the Dirac gap value modulation. Full article

The antiferromagnetic ordering that MnBi${}_2$Te${}_4$ shows makes it invariant with respect to the combination of the time-reversal and primitive-lattice translation symmetries, giving rise to its topologically nontrivial nature and a number of fundamental phenomena. At the same time, the possibility to control the electronic and magnetic properties of this system can provide new effective ways for its application in devices. One of the approaches to manipulate MnBi${}_2$Te${}_4$ properties is the partial substitution of magnetic atoms in the compound with atoms of non-magnetic elements, which inevitably affect the interplay of magnetism and band topology in the system. In this work, we have carried out theoretical modelling of changes in the electronic structure that occur as a result of increasing the concentration of Sn atoms at Mn positions in the (Mn${}_{1-x}$Sn${}_x$)Bi${}_2$Te${}_4$ compound both using Korringa–Kohn–Rostoker (KKR) Green’s function method as well as the widespread approach of using supercells with impurity in DFT methods. The calculated band structures were also compared with those experimentally measured by angle-resolved photoelectron spectroscopy (ARPES) for samples with x values of 0, $0.19$, $0.36$, $0.52$ and $0.86$. We assume that the complex hybridization of Te-p${}_z$ and Bi-p${}_z$ orbitals with Sn and Mn ones leads to a non-linear dependence of band gap on Sn content in Mn positions, which is characterized by a plateau with a zero energy gap at some concentration values, suggesting possible topological phase transitions in the system. Full article