Depopulation of the Mn2+ state in ZnO:Mn upon illumination, monitored by quenching of the Mn 2+ EPR signal intensity, was observed at temperatures below 80 K. Mn 2+ photoquenching is shown to result from the Mn 2+ → Mn 3+ ionization transition, promoting one electron to the conduction band. Temperature dependence of this process indicates the existence of an energy barrier for electron recapture of the order of 1 meV. GGA+U calculations show that after ionization of Mn 2+ a moderate breathing lattice relaxation in the 3+ charge state occurs, which increases energies of d(Mn) levels. At its equilibrium atomic configuration, Mn 3+ is metastable since the direct capture of photo-electron is not possible. The metastability is mainly driven by the strong intra-shell Coulomb repulsion between d(Mn) electrons. Both the estimated barrier for electron capture and the photoionization energy are in good agreement with the experimental values.

MnBi2Te4/(Bi2Te3)n materials system has recently generated strong interest as a natural platform for realization of the quantum anomalous Hall (QAH) state. The system is magnetically much better ordered than substitutionally doped materials, however, the detrimental effects of certain disorders are becoming increasingly acknowledged. Here, from compiling structural, compositional, and magnetic metrics of disorder in ferromagnetic MnBi2Te4/(Bi2Te3)n it is found that migration of Mn between MnBi2Te4 septuple layers (SLs) and otherwise non-magnetic Bi2Te3 quintuple layers (QLs) has systemic consequences - it induces ferromagnetic coupling of Mn-depleted SLs with Mn-doped QLs, seen in ferromagnetic resonance as an acoustic and optical resonance mode of the two coupled spin subsystems. Even for a large SL separation (n ≳ 4 QLs) the structure cannot be considered as a stack of uncoupled two-dimensional layers. Angle-resolved photoemission spectroscopy and density functional theory studies show that Mn disorder within an SL causes delocalization of electron wave functions and a change of the surface band structure as compared to the ideal MnBi2Te4/(Bi2Te3)n. These findings highlight the critical importance of inter- and intra-SL disorder towards achieving new QAH platforms as well as exploring novel axion physics in intrinsic topological magnets.

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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 Kα 1 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.

Nanoindentation measurements were performed for a single PbTe crystal grown by self-selecting vapour growth method and characterized by X-ray diffraction. The microhardness and Young's modulus were determined for a few loads applied along the [001], [011] and [111] high symmetry directions for carefully oriented, 2 mm thick crystal plates. An anisotropy of two parameters has been suggested and compared with available literature data. The present results qualitatively confirm the theoretical predictions for a rock salt type crystal (PbS). The microhardness anisotropy value is in an agreement with recently determined, relevant value for (Pb,Cd)Te solid solution.

Zinc oxide crystals were grown by CVT contactless technique and thermally annealed in the air, nitrogen or oxygen atmospheres, or zinc or arsenic vapours. Wide ranges of annealing times and temperatures were applied. The variety of morphology and quality of the crystal surface was investigated by AFM and XRD. It was found, that thermal annealing in the air, nitrogen, oxygen and zinc resulted in similar evolution of the crystal surface, although there are observed differences in the rate of the changes. The annealing in zinc vapour resulted in roughness (RMS) lower than 1 nm. The annealing in arsenic vapour leads to degradation of the crystal surface. The improvement of the surface was not observed in case of thermal annealing of the rough ZnO surfaces obtained by ALE homoepitaxy on the smooth CVT as-grown ZnO surfaces.

Extensive studies of physical properties and growth process of ZnO crystals are motivated by unique electrical and optical properties of this material. In the present work, the defect-structure characteristics of a bulk zinc oxide crystal grown by Contactless Chemical-Vapour-Transport method are studied. The macromosaic spread is found to be of the order of 1°. The values of lattice parameters and axial ratio in the main part of the crystal perfectly agree with literature data. Changes of the colour observed along the crystal correlates with intentional vapour pressure variation during the growth.

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