We demonstrate that the metallic topological surface states wrap on all sides the three-dimensional topological crystalline insulator SnTe. This is achieved by studying oscillatory quantum magnetotransport and magnetization at tilted magnetic fields, which enables us to observe simultaneous contributions from neighboring sample sides. Taking into account pinning of the Fermi energy by the SnTe reservoir, we successfully describe theoretically the de Haas–van Alphen oscillations of magnetization. The determined $\pi$–Berry phase of surface states confirms their Dirac fermion character. We independently observe oscillatory contributions of magnetotransport and magnetization originating from the bulk SnTe reservoir of high hole density. It is concluded that the bulk and surface Landau states exist in parallel. Our main result that the bulk reservoir is surrounded on all sides by the topological surface states has a universal character.

A series of FeSe_0.5Te_0.5 bulk samples have been prepared using the high gas pressure and high-temperature synthesis (HP-HTS) method to optimize the growth conditions for the first time and investigated for their superconducting properties using structural, microstructure, transport, and magnetic measurements to reach the final conclusions. Ex situ and in situ processes are used to prepare bulk samples under a range of growth pressures using Ta-tube and without Ta-tube. The parent compound synthesized by convenient synthesis method at ambient pressure (CSP) exhibits a superconducting transition temperature of 14.8 K. Our data demonstrate that the prepared FeSe_0.5Te_0.5 sealed in a Ta-tube is of better quality than the samples without a Ta-tube, and the optimum growth conditions (500 MPa, 600 °C for 1 h) are favorable for the development of the tetragonal FeSe_0.5Te_0.5 phase. The optimum bulk FeSe_0.5Te_0.5 depicts a higher transition temperature of 17.3 K and a high critical current density of the order of >10⁴ A/cm² at 0 T, which is improved over the entire magnetic field range and almost twice higher than the parent compound prepared using CSP. Our studies confirm that the high-pressure synthesis method is a highly efficient way to improve the superconducting transition, grain connectivity, sample density, and pinning properties of a superconductor.

The exchange bias (EB) effect and an appearance of the Griffiths phase (GP) were found in half-doped cobaltite $\mathrm{G}{\mathrm{d}}_{0.5}\mathrm{S}{\mathrm{r}}_{0.5}\mathrm{Co}{\mathrm{O}}_{3-\delta }$ exhibiting a significant quenched disorder due to the ion size mismatch between Sr and Gd. The disorder weakens the ferromagnetic (FM) interactions between Co ions, leading to low Curie temperature $T_C=90\mathrm{K}$ and to a highly nonhomogenous magnetic state above $T_C$. A clear GP behavior was detected in the temperature range between $T_C$ and the Griffiths temperature $T_G=225\mathrm{K}$. Moreover, this GP demonstrates a unique feature; namely, the appreciable EB effect exists concomitantly within the GP, suggesting coexisting FM and antiferromagnetic nanocluster phases. It was found that the EB exists in $\mathrm{G}{\mathrm{d}}_{0.5}\mathrm{S}{\mathrm{r}}_{0.5}\mathrm{Co}{\mathrm{O}}_{3-\delta }$ for the entire temperature range below $T_G=225\mathrm{K}$, in contrast to the limited low-temperature EB observed so far in perovskite cobaltites. The EB has a different nature in the FM cluster phase below $T_C$ and in the GP in temperature interval $T_C<T<T_G$. The cooling field effect on EB was examined in the GP, and the size of FM clusters was determined to be equal to 6.5 nm.

Magnetic ordering temperature, initial splitting and effective g-factor of the ground quasi-doublet of a Tb³⁺ ion were determined by investigating the heat capacity and ESR in a TbAl₃(BO₃)₄ single crystal. The parameters of the magnetic interaction were calculated.

High-pressure growth is a unique method to improve the sample quality and size. Here, we have used the high gas pressure and high-temperature synthesis (HP-HTS) method to grow CaKFe ₄ As ₄ (1144) bulks and investigated their superconducting properties using structural, microstructural, transport, and magnetic studies. The microstructural analysis demonstrates that 1144 samples prepared by HP-HTS have improved the sample density and grain connectivity. The transition temperature $({{T}_c^{onset}})$ of 1144 bulks prepared by HP-HTS is increased up to 35.2 K with a transition width ( ΔT ) of 1 K, which is remarkably comparable to the reported 1144 single crystal. Additionally, the critical current density ( J_c ) is enhanced by almost one order of magnitude compared with the parent compound prepared by the conventional synthesis process at ambient pressure (CSP), which could be attributed to the improved sample density and effective pinning centers. Our study demonstrates that the sample quality and superconducting properties of various iron-based superconductors can be enhanced by applying the HP-HTS approach, and further research is demanded in this direction.

The enhanced performance of superconducting FeSe_0.5Te_0.5 materials with added micro-sized Pb and Sn particles is presented. A series of Pb- and Sn-added FeSe_0.5Te_0.5 (FeSe_0.5Te_0.5 + xPb + ySn; x = y = 0–0.1) bulks are fabricated by the solid-state reaction method and characterized through various measurements. A very small amount of Sn and Pb additions (x = y ≤ 0.02) enhance the transition temperature (T_c^onset) of pure FeSe_0.5Te_0.5 by ~1 K, sharpening the superconducting transition and improving the metallic nature in the normal state, whereas larger metal additions (x = y ≥ 0.03) reduce T_c^onset by broadening the superconducting transition. Microstructural analysis and transport studies suggest that at x = y > 0.02, Pb and Sn additions enhance the impurity phases, reduce the coupling between grains, and suppress the superconducting percolation, leading to a broad transition. FeSe_0.5Te_0.5 samples with 2 wt% of cometal additions show the best performance with their critical current density, J_c, and the pinning force, F_p, which might be attributable to providing effective flux pinning centres. Our study shows that the inclusion of a relatively small amount of Pb and Sn (x = y ≤ 0.02) works effectively for the enhancement of superconducting properties with an improvement of intergrain connections as well as better phase uniformity.