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The effects of heat treatment temperature, time and isostatic pressure on the grain connectivity and superconducting properties of Mg11B2 wires prepared using nano-amorphous isotopic boron powder (11B) have been investigated. The article presents detailed studies of the Mg11B2 material structure of the wires using scanning electron microscope (SEM). Heat treatment at low and high temperature for different annealing time and isostatic pressure does not create an internal macro-defect that disrupts connectivity in the Mg11B2 superconducting wires. Our study shows that dense longitudinal superconducting layers are formed at high annealing temperature of 800 °C for 60 min. Formation of dense longitudinal superconducting layers under high isostatic pressure (HIP) allow improved grain connectivity and high density of pinning centers and as a result, high engineering critical current density, Jec, at 4.2 K has been achieved. Also, high upper critical field (Bc2) and high irreversible magnetic field (Birr) were obtained using HIP process while superconducting transition temperature (Tc) was not significantly affected. Better grain connectivity obtained using high annealing temperature and long annealing time under low isotopic pressure leads to Jec enhancement at high magnetic fields at 20 K. Our results show that the annealing temperature of 800 °C for 60 min under isostatic pressure of 1 GPa yields the required Jec of 25 A/mm2 and 50 A/mm2 for ITER applications in magnetic fields of 8 T and 7 T, respectively. The promising results obtained in this work could pave the way for designing low activation superconducting Mg11B2 wires to be considered for next generation fusion magnets.

Half-Heusler phase HoPtSb was studied by means of powder X-ray diffraction, scanning electron microscopy with energy-dispersive X-ray spectrometry, high-resolution transmission electron microscopy (HRTEM), heat capacity, magnetization, electrical resistivity and magnetoresistance. Measurements were performed in temperature range 2–300 K and magnetic fields up to 14 T. The results revealed significant atomic disorder in the crystal structure of this compound, and indicated that the electrical transport in HoPtSb is noticeably affected by scattering conduction electrons on structural inhomogeneities. Due to large value of the resistivity accompanied by small overall change of resistivity with changing temperature the high-temperature behavior was attributed to disorder-induced violation of the Matthiessen’s rule. In turn, at low temperatures, strong magnetic field of 14 T disclosed resistivity upturn reminiscent of Altshuler-Aronov quantum correction observed in disordered metallic systems.

The relaxation processes of the adiabatic temperature changes (ΔTad) at the phase transitions in Ni45Mn43CoSn11, Ni50Mn36.5In13.5, and Ni50Mn35In14.25B0.75 Heusler alloys with different magnetic structures have been studied using a direct extraction method in magnetic fields up to 14 T. It has been found that ΔTad exhibits short relaxation times (less than 10−1 (s)) in the vicinity of the second order phase transitions at the Curie temperatures. The relaxation times of the first order martensitic transitions strongly depend on the latent heat of the transition and can be characterized by a logarithmic law.