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Heusler Ni-Mn-Ga alloys with martensitic transformation being multiferroic materials are touted for magneto- and multi-caloric effect (MCE) and moreover, they exhibit magnetic shape memory (MSM) phenomena. MCE benefits from high saturation magnetization and also large variability and sensitivity of transformation temperatures on alloying. In contrast, MSM phenomena are limited by low temperatures of both ferromagnetic and ferroelastic transformations. In an attempt to increase the transformation temperatures and to understand the physical fundamentals beyond transformation variations and magnetic ordering, we experimentally investigate the magnetic and transformation properties in Ni2MnGa alloyed with transitional elements spanning from Cr to Cu. These elements are consecutively substituted on Ni, Mn, and Ga sites, to establish the effect of positional substitution and elemental evolution. The elemental dependence of saturation magnetization, magnetocrystalline anisotropy, Curie temperature, and martensitic transformation temperatures are compared with (non-)stoichiometric Ni-Mn-Ga Heusler compounds. The observed behavior is complex and there are no clear trends of transformation temperatures as a function of the number of valence (non-bonding) electrons per atom, however, the saturation magnetization at 10K and Curie temperature seems to follow the Pauli-Slater curve. Obtained results can serve as useful rectification for the theoretical prediction of new Ni-Mn-Ga-X Heusler alloys.

Systematic doping by transition elements Fe, Co and Ni on each site of Ni2MnGa alloy reveal that in bulk material the increase in martensitic transformation temperature is usually accompanied by the decrease in ferromagnetic Curie temperature, and vice versa. The highest martensitic transformation temperature (571 K) was found for Ni50.0Mn25.4(Ga20.3Ni4.3) with the result of a reduction in Curie temperature by 55 K. The highest Curie point (444 K) was found in alloy (Ni44.9Co5.1)Mn25.1Ga24.9; however, the transition temperature was reduced to 77 K. The dependence of transition temperature is better scaled with the Ne/a parameter (number of non-bonding electrons per atom) compared to usual e/a (valence electrons per atom). Ne/a dependence predicts a disappearance of martensitic transformation in (Ni45.3Fe5.3)Mn23.8Ga25.6, in agreement with our experiment. Although Curie temperature usually slightly decreases while the martensitic transition increases, there is no significant correlation of Curie temperature with e/a or Ne/a parameters. The doping effect of the same element is different for each compositional site. The cascade substitution is discussed and related to the experimental data.

Ferromagnetic shape-memory CoNiGa alloys have attracted much scientific interest due to their potential alternative use as high-temperature shape-memory alloys, bearing a high prospect for actuation and damping applications at elevated temperatures. Yet, polycrystalline CoNiGa, due to strong orientation dependence of transformation strains, suffers from intergranular fracture. Here, two multi-grain CoNiGa samples were prepared by a novel hot extrusion process that can promote favourable grain-boundary orientation distribution and improve the material's mechanical behaviour. The samples were investigated by multiple methods and their micro structural, magnetic, and mechanical properties are reported. It is found that a post-extrusion solutionising heat treatment leads to the formation of a two-phase oligocrystalline homogeneous microstructure consisting of an austenitic parent B2 phase and gamma-CoNiGa precipitates. Reconstruction of the full 3D grain morphology revealed large, nearly spherical grains with no low-angle grain boundaries throughout the entire sample volume. The presence of gamma precipitation affects the transformation behaviour of the samples, by lowering the martensitic transformation temperature, while, in conjunction with the oligocrystalline microstructure, it improves the ductility. Controlling the composition of the B2 matrix, as well as the phase fraction of the gamma phase, is thus crucial for the optimal behaviour of the alloys. (c) 2020 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http:// creativecommons.org/licenses/by-nc-nd/4.0/).

Critical currents Ic of several commercial REBaCuO superconducting tapes, prepared by various producers, were tested inductively (vibrating sample magnetometer in magnetic fields up to 9 T). Measurements were performed before and after neutron irradiation. Irradiation was conducted in the LVR-15 fission reactor at the Research Centre qež with doses of 1 × 10 22 m -2 and 2.1 × 10 22 m -2 . After irradiation, we observed a slight decrease in Ic around the self-field in all tapes. At higher magnetic fields, neutron irradiation caused a large variation in Ic, with some tapes showing a strong enhancement, some tapes showing a moderate effect, whilst no effect or even an Ic degradation appeared in the remainder. The irradiation effect depended on the pinning medium, measurement temperature, and magnetic field.

The RE-123 tapes represent the most advanced product in the field of high temperature superconductors, developed for transport of high electric currents. Although this product has already proceeded to the stage of industrial production, the variety in techniques employed by different manufacturers make the final products by far not identical. We studied electromagnetic properties of a series of 21 tapes from main global wire manufacturers. The tapes were tested by magnetic induction technique (vibrating sample magnetometer, VSM) and by a transport current measurements. The aim was to find the best candidates for superconducting coils for fusion reactors. Engineering currents were deduced from magnetic hysteresis loops measured by VSM at 10 K, 50 K, and 77 K. The data for 77 K were compared with the results of direct transport experiments done at the same temperature. Current transport experiments also provided information on the current anisotropy. The VSM tests were repeated after neutron irradiation of the tapes by neutron fluence of 2.12 × 1018 cm−2. A significant enhancement of engineering currents was observed in magnetic fields above 0.5 T in all investigated tapes and temperatures. The enhancement, similarly as the engineering current, was roughly exponential function of temperature.

Light-weight ferromagnetic Co-Ni-Al:Ti composites were consolidated by spark plasma sintering. Powders of ball-milled Co-Ni-Al and gas atomized α-Ti were mixed together in three different ratios and spark plasma sintered at 950°C, using two sintering times, i.e. dwell times at the maximal temperatures: 1 and 5min. The composites were successfully compacted and new intermetallic phases were formed at the Co-Ni-Al/Ti interfaces. The composites exhibit favourable flexural strength, excellent high-temperature stability, and relatively high saturation magnetization. On the other hand, the newly emerged intermetallic phases are non-ferromagnetic, which slightly deteriorates the magnetic properties. Keywords: Metal–metal composites, Spark plasma sintering, Light metals, Ferromagnetic alloys, Mechanical properties

The combination of enlarged magnetic coercivity and magnetic shape memory (MSM) functionality is essential for novel magnetomechanical effects in MSM alloys. We found that increasing the density of thermal antiphase boundaries (APBs) provides a method to increase the magnetic coercivity without deteriorating the MSM functionality. APB density was controlled by different heat treatments in Ni-Mn-Ga(-B) MSM single crystals with five-layered modulated martensite structure. Slow cooling ~1 K/min of Ni-Mn-Ga through the B2'-L21 transition resulted in a low density (

The combination of enlarged magnetic coercivity and magnetic shape memory (MSM) functionality is essential for novel magnetomechanical effects in MSM alloys. We found that increasing the density of thermal antiphase boundaries (APBs) provides a method to increase the magnetic coercivity without deteriorating the MSM functionality. APB density was controlled by different heat treatments in Ni–Mn–Ga (–B) MSM single crystals with five-layered modulated martensite structure. Slow cooling ∼1 K/min of Ni–Mn–Ga through the B2′–L21 transition resulted in a low density ( 1/micrometer) of APBs observed by magnetic force microscopy and low coercivity

In bulk high-temperature superconductors, Ag is usually used as an additive thus improving mechanical performance. In MgB2 doped with Ag, the Ag reacts with Mg, forming Mg–Ag phases acting as a vortex pinning medium. In this work, we analyze the electromagnetic and pinning properties of bulk MgB2 doped with 1 wt% MgB4, 4 wt% Ag, and 1 wt% Dy2O3, prepared at the Shibaura Institute of Technology (SIT), Tokyo. In three compounds of MgxB2 + 4 wt% Ag with x = 1, 1.075, and 1.1, the effect of Mg excess was studied. The magnetic moment was measured by a vibrating sample magnetometer (VSM). Pinning was studied in terms of a pinning diagram, i.e. the field dependence of the normalized pinning force density, F n = F/F max. In all studied samples, the peak of the F n (b) dependence (b= B/B irr, B irr being the irreversibility field) was observed at around b= 0.2, indicating a prevailing flux pinning at grain boundaries. A slight shift of the peak with decreasing temperature indicated a defect size distribution in the pinning landscape. Transmission electron microscopy (TEM) showed a granular structure of all samples composed of MgB2 grains of about 230 nm (average size), with ensembles of small grains (22 nm in average) of Ag3Mg, AgMg, Ag, Dy2O3, and MgB4. While the large MgB2 grains control the main pinning mechanism, the small precipitates seem to determine details of the current flow through the grain boundaries.

Magnetic properties of Ni 46 Mn 24 Ga 22 Co 4 Cu 4, (Ni 45 Mn 23 Ga 22 Co 5 Cu 5 , Ni 46 Mn 22.5 Ga 23 Co 5 Cu 3.5 ) tetragonal martensites with c / a ≈ 1.14 exhibiting near 10% magnetic field-induced strain (MFIS) were investigated between 10 and 500 K and up to 9 T field. The (001) easy plane magnetocrystalline anisotropy with K 1 (300 K)= − 1.95 ∙ 10 5 J ∙ m − 3 ( K 2 K 1 |, K 3 K 1 |, M S (300 K) = 63 Am 2 /kg) was about 30% lower than in the non-doped Ni 50.5 Mn 30.4 Ga 19.1 reference, which can be related to a reduced c / a ratio in the doped material. In spite of different type of magnetocrystalline anisotropy compared to 10M martensite, the mechanism of MFIS is the same, i.e. with the typical first-quadrant magnetization hysteresis and {101} twin boundary motion.