Fermi level dependence of magnetism and magnetotransport in the magnetic topological insulators Bi2_{2}Te3_{3} and BiSbTe3_{3} containing self-organized MnBi2_{2}Te4_{4} septuple layers

The magnetic coupling mechanisms underlying ferromagnetism and magnetotransport phenomena in magnetically doped topological insulators have been a central issue to gain controlled access to the magneto-topological phenomena such as quantum anomalous Hall effect and topological axion insulating state. Here, we focus on the role of bulk carriers in magnetism of the family of magnetic topological insulators, in which the host material is either Bi$_{2}$Te$_{3}$ or BiSbTe$_{3}$, containing Mn self-organized in MnBi$_{2}$Te$_{4}$ septuple layers. We tune the Fermi level using the electron irradiation technique and study how magnetic properties vary only through the change in carrier density. Ferromagnetic resonance spectroscopy excludes bulk magnetism based on a carrier-mediated process. Furthermore, the magnetotransport measurements show that the anomalous Hall effect is dominated by the intrinsic and dissipationless Berry-phase driven mechanism, with the Hall resistivity enhanced near the bottom/top of the conduction/valence band, due to the Berry curvature which is concentrated near the avoided band crossings. These results demonstrate that the anomalous Hall effect can be effectively managed, maximized, or turned off, by adjusting the Fermi level.Comment: 11 pages, 7 figure

Coexistence of Anomalous Hall Effect and Weak Net Magnetization in Collinear Antiferromagnet MnTe

Anomalous Hall effect (AHE) plays important role in the rapidly developing field of antiferromagnetic spintronics. It has been recently discussed that it can be a feature of not only uncompensated magnetic systems but also in altermagnetic materials. Hexagonal MnTe belongs to this appealing group of compounds exhibiting AHE and is commonly perceived as magnetically compensated. Here, we demonstrate that bulk form of MnTe exhibits small but detectable magnetic moment correlating with hysteretic behaviour of the AHE. We formulate a phenomenological model which explains how this feature allows to create a disbalance between states with opposite N\'eel vector and prevent the AHE signal from averaging out to zero. Moreover, we show how the dependence of AHE on the N\'eel vector arises on microscopical level and highlight the differences in Berry curvature between magnetically compensated and uncompensated systems

Study of the effect the rate of addition of the antisolvent on the crystallization of the CL-20

W niniejszej pracy w ramach optymalizacji procesu krystalizacji 2,4,6,8,10,12-heksanitro– 2,4,6,8,10,12-heksazaizowurcytanu (CL-20) metodą wytrącania z układu rozpuszczalnik/ nierozpuszczalnik, określono wpływ szybkości dozowania nierozpuszczalnika na wydajność oraz czystość polimorficzną otrzymywanego produktu. Podsumowując rezultaty badań stwierdzono, że im szybciej dozowany jest nierozpuszczalnik tym większe jest, generowane w roztworze macierzystym, przesycenie, co w efekcie przekłada się na zwiększenie szybkości nukleacji. Przewaga procesu tworzenia nowych zarodków powoduje zmniejszenie szybkości wzrostu kryształów, co ma wpływ na rozkład ziarnowy finalnego produktu krystalizacji. Krótszy czas prowadzenia procesu powoduje, że powstała, jako pierwsza forma, kinetycznie stabilna – β ulega w mniejszym stopniu transformacji do formy stabilnej termodynamicznie – ε, niż ma to miejsce przy dłuższym czasie prowadzenia procesu.In this paper, in order to optimize precipitation process of 2,4,6,8,10,12-hexanitro– 2,4,6,8,10,12-hexaazaisowurtzitane, from solvent/antisolvent system, effect of antisolvent addition rate on the yield and polymorphic purity of the obtained product, was determined. It was found that higher dispensing rate of the anti-solvent causes higher supersaturation in the mother liquor. This increases the nucleation rate. Dominance of the process of creating new seed reduces the rate of crystal growth. This affects the size distribution of the final crystallization product. Reduced time of process causes that first formed, kinetically stable, polymorph β, is transformed into a thermodynamically stable ε form with a lower yield, than is the case for a longer time of process

Friction Sensitivity of the ε-CL-20 Crystals Obtained in Precipitation Process

The purpose of this work was to obtain samples of CL-20 by precipitation process in a solvent/nonsolvent system, under variable process parameters such as: antisolvent kind, time of nonsolvent addition, stirrer speed, mass of seeded crystals of ε-CL-20. Received samples were studied in the aspect of their sensitivity to friction. As the results of the crystallization processes were prepared crystals of different sizes and shapes depend on applied parameters. It was affirmed, that applied antisolvent has essential influence on type of received crystals. CL-20 crystals of cuboid shape and sizes of 80-200 μm were obtained by recrystallization from ethyl acetate/chloroform. As the result of the recrystallization from ethyl acetate/xylene crystals with rounded edges were obtained. Crystals, from both samples, were mostly single and showed the lowest sensitivity to friction. Also, the crystals of irregular shape and sharp-edged agglomerates were obtained from systems with n-heptane, isooctane, cyclohexane and toluene, which revealed the highest friction sensitivities

Substrates Grown from the Vapor for ZnO Homoepitaxy

The novel method of preparation of epi-ready ZnO substrates is demonstrated. The substrates were made of unique ZnO crystals grown by chemical vapor transport method using hydrogen as the transport agent. The effect of low-level doping (Mn, Co, Cu, and V) on the structural quality of the crystals was investigated. Atomic layer deposition was used to verify usability of the substrates for homoepitaxy. The thermal annealing prior to the atomic layer deposition process and effect of thermal annealing of the epitaxial layers was studied. The X-ray diffraction and atomic force microscopy methods were applied to study the structural quality of the ZnO layers. Detection of the dopants in the substrates by secondary ion mass spectroscopy made possible the measurement of the thickness of the layers. The obtained root mean square roughness for both the substrates and layers ranged between 0.2 nm and 5 nm, and was dependent on the sample crystallographic orientation and sequence of polishing and annealing procedures. The optimal recipe for the epi-ready substrate preparation was formulated

Influence of annealing on the electronic structure of ZnO bulk crystals – a photoemission and luminescence study

Photoemission Spectroscopy was applaed to determine valence band electronic structure of the clean freshly cleaved ZnO bulk crystal surface

The Young modulus and microhardness anisotropy in (Pb,Cd)Te solid solution crystallizing in the rock salt structure and containing 5% of Cd

A single crystal of (Pb,Cd)Te solid solution with Cd content equal to 5% was grown by self-selecting vapour growth technique and characterized by powder X-ray diffraction using the X'Pert PANalytical diffractometer and Cu K_{α₁} radiation. The X-ray diffraction pattern refinement demonstrated the fcc structure of the rock-salt type of investigated sample, no precipitates or other crystal phases were detected. The sample chemical composition was determined on the basis of measured lattice parameter value. Next, the Young modulus and microhardness were determined by the nanoindentation for carefully prepared, (001), (011) and (111)-oriented single crystal plates. The slight anisotropy of two parameters mentioned above has been found and compared with available literature data

Substrates Grown from the Vapor for ZnO Homoepitaxy

The novel method of preparation of epi-ready ZnO substrates is demonstrated. The substrates were made of unique ZnO crystals grown by chemical vapor transport method using hydrogen as the transport agent. The effect of low-level doping (Mn, Co, Cu, and V) on the structural quality of the crystals was investigated. Atomic layer deposition was used to verify usability of the substrates for homoepitaxy. The thermal annealing prior to the atomic layer deposition process and effect of thermal annealing of the epitaxial layers was studied. The X-ray diffraction and atomic force microscopy methods were applied to study the structural quality of the ZnO layers. Detection of the dopants in the substrates by secondary ion mass spectroscopy made possible the measurement of the thickness of the layers. The obtained root mean square roughness for both the substrates and layers ranged between 0.2 nm and 5 nm, and was dependent on the sample crystallographic orientation and sequence of polishing and annealing procedures. The optimal recipe for the epi-ready substrate preparation was formulated