Here we demonstrate that a ferromagnetic shape memory can be tuned conveniently by volume proportions within Heusler-type Fe47-xMn24+xGa29 (x = 8, 6, 4, 2, and 0 at. %) alloys over an extended temperature range. Preliminary X-ray diffraction experiments indicate that the Fe47-xMn24+xGa29 alloys crystallize into a B2 cubic structure with space group Pm-3m for all compositions. Samples with compositions of x = 0 - 4 at. % show the co-existence of two cubic structures (B2 and L21). The temperature dependence of magnetization M(T) measurements on Fe47-xMn24+xGa29 alloys under cooling-heating processes showed a moderate to an exceptionally large temperature hysteresis in a wider temperature range of 70-340K, corresponding to the first-order diffusionless martensitic-to-austenite phase transformations. The M(T) curves obtained at various magnetic fields demonstrated that the magnitude and direction of temperature hysteresis is modified by volume proportions of Fe-Mn constituents. At 5, 150 and 300K, hysteresis loop shows ferromagnetic (FM) behavior and the coercivity and remanence values vary with temperature and Mn content due to large exchange bias effects. Further ac magnetic susceptibility of Fe47-xMn24+xGa29 measurements show a cusp with a maximum below 70K corresponding to an antiferromagnetic (AFM) transition. Thermal shift of the AFM transition is attributed to the dominant AFM-FM interactions pertaining to the pinning efficiency at the interface between Fe and Mn. These findings provide a comprehensive understanding of AFM spin structure and ferromagnetic shape memory behavior in Fe47-xMn24+xGa29 across cryogenic to 350K temperatures.

In this article, a magnetocaloric effect of electrodeposited Ni-Mn-Ga -based Heusler nanowires is presented using the indirect approach. The structural characterization revealed that the prepared nanowires exhibit a martensitic transformation capability above room temperature (at 350 K). The martensitic transformation results in a relatively high magnetic entropy change of > 2.5 J.kg-1. K-1. Moreover, the magnetocaloric effect analysis reveals a maximum magnetic entropy change at a moderate magnetic field of only 2 T. The pre-sented cheap fabrication method, together with the strong magnetocaloric response of the nanowires at moderate magnetic fields, opens up new possibilities in the field of nanosized Heusler alloys operating as refrigerants, actuators, or sensors (c) 2023 Elsevier B.V. All rights reserved.

We report the structural, magnetic, and magnetocaloric characterization of glass-coated Ni42.9Mn37.1Sn20.0 microwires produced by the Taylor-Ulitovsky method. Microwire samples crystallized into a single-phase austenite with the L21-type crystal structure (space group Fm3̄m, lattice parameter a ≈ 6.02 Å) and a Curie temperature of 349 K. A distinctive feature of the produced microwires is that saturation magnetization is reached at a very low magnetic field (∼0.15 T). For a magnetic field change of 3 T, the produced microwires showed a reversible maximum magnetic entropy change |ΔSM|max of 2.3 J kg−1 K−1 and a refrigerant capacity of 197 J kg−1, which are similar to the values reported by other austenitic NiMnSn alloys produced by rapid quenching techniques.

Magnetic characterization of ferromagnetic Ni-Fe-Ga shape memory nanowires using a temperature-dependent FORC analysis is shown. The hysteresis loops' shape indicates a magnetic anisotropy that is governed by the magnetostatic interaction among neighboring nanowires. FORC measurement proved that the Ni-Fe-Ga nanowires' array is a multi-domain and highly interacting system. The FORC analysis shows a minimal coercivity distribution that points to a uniform and homogeneous nanowires' array. The change of the vertical spread of the FORC distribution divergence at about 395 K supports the ferromagnetic shape memory behavior and the structural transformation of the presented nanowires. The previous results are also supported by a unique TFORC analysis, showing structural changes within the transformation temperature region. (C) 2021 Elsevier B.V. All rights reserved.

We report on the production and characterization of Heusler-based Ni2FeGa microwires exhibiting two - way shape memory effect. The microwires are characterized by a monocrystalline structure with a strong preferred crystallographic orientation that shows [1 1 1] axis parallel to the wire's axis for high-temperature L2(1) austenite phase, while the [0 1 7] axis is preferred for low-temperature monoclinic phase. Variation of crystallographic axis (and corresponding easy magnetization axis) leads to 1600% variation of magnetic permeability due to a 2% strain in axial direction. Such straining is reversible immediately after production without the necessity of further thermal treatment. These properties give the microwire function of very sensitive SMART actuators that can be easily produced in a large amount.

In this paper, the authors present studies on YBCO BSS alloyed with cerium, also in combination with rare earth elements (RE) for inducing chemical pining, which were prepared in their research laboratories or in a commercial company CAN superconductor using top-seeded melt-growth (TSMG) or top-seeded infiltration-growth processes. The relationship between the local microstructure and the superconducting properties of the commercially produced TSMG YBCO BSS with the addition of CeO2 was investigated. It is important to have cerium distributed homogeneously in the starting pellet of the pressed powders to grow single-grain YBCO to ensure cerium activity on the micrometer scale. Knowledge of the relationship of local microstructure and superconducting properties in a broad temperature range will be useful in practical applications of Y123 bulk superconductors. Micro structural analysis showed that Y211 particles were in-homogeneously arranged within the commercially prepared Y123 single-grain bulk.

The relationship between local microstructure and superconducting properties of commercially prepared YBa2Cu3O7-delta single-grain bulk superconductor was investigated. The small samples for magnetization measurements were taken from the beginning and end of the a-growth sector and the c-growth sector as well as from the beginning and end of a/a-growth sector boundary. The field dependence of the magnetic moment was measured at temperatures starting from liquid helium (4.2 K) to liquid nitrogen (77 K) using the commercial Magnetic Property Measurement System with a magnetic field of up to 7 and 18 T. The microstructure was analysed using polarised light optical microscopy and scanning electron microscopy. The quantitative microstructural data were determined using an image processing software package. Microstructure analysis was focused on the size and volume fraction of Y2BaCuO5 particles as well as on the characterisation of subgrain structure. These measurements showed that not only inhomogeneous distribution of Y2BaCuO5 particles had influence on the critical current density but it can also be significantly affected by the subgrain structure within the bulk or by local contamination of YBa2Cu3O7-delta from the seed during fabrication process. It was observed that the critical current density along the a/a-growth sector boundary could be substantially higher in comparison to the other parts of the bulk and this behaviour can be related to the subgrain structure in the sample.

TmB4 is an anisotropic, metallic magnetic system with geometrical frustration of the Shastry-Sutherland type. Here an experimental study of the magnetocaloric effect (MCE) in Lu-doped Tm1-xLuxB4 (x = 0.06, 0.30), evaluated from the temperature dependence of heat capacity and magnetization curves at 2 K, is presented. The results are described within a theoretical model based on an extended Ising Hamiltonian which considers interactions up to the fourth-next-nearest neighbors. Model parameters were optimized to achieve the best match to the experimental results over the whole range of Lu3+ ion concentrations. After optimization a good quantitative agreement with the adiabatic temperature change and a good qualitative agreement with magnetization curves is obtained. Our study shows that the efficiency of the MCE can be tuned by dilution with nonmagnetic Lu ions. The theoretical model developed could be used to design new magnetocaloric materials.

The influence of TiO2 microfibres doping on superconducting properties (critical temperature T-c and critical current density J(c)) of single-grain bulk GdBa2Cu3O7-delta (GdBCO) high-temperature superconductor was investigated. In this study, we prepared pure GdBCO and GdBCO+TiO2 superconductor via the top-seeded melt growth method in air. The ceramic fibres were prepared using the electros pinning method and were added in the small quantity (0.05 wt%) for the increase of density of flux pinning centres. Magnetization measurements were performed on the specimens taken from several different locations of both studied samples. The experimental results showed that TiO2 addition do affect the T-c along with the decrease of J(c).

The papers in this special section were presented at the 10th International Workshop on Processing and Applications of Superconducting (RE)BCO Large Grain Materials (PASREG 2017) held on December 11–12, 2017 at the Shibaura Institute of Technology, Tokyo, Japan.

YBCO bulk single-grain samples with and without cerium oxide addition, were prepared by the two-step top seeded infiltration growth. The microstructure observations showed that cerium oxide addition led to formation of small Y2BaCuO5 (Y211) particles in the YBa2Cu3O7 single-grain matix. On the other hand, the sample without cerium oxide addition exhibited clusters of large Y211 particles. Observed difference in Y211 paricles led to significantly different size of a/c-oxygenation cracks. While the mean length of a/c-cracks in the sample with cerium oxide addition was several hundred micrometers, it was smaller than 50 mu m in the sample without cerium oxide addition. It was shown that the clusters of large Y211 particles can effectively prevent extension of oxygenation a/c-cracks. The trapped magnetic field measured at 77 K is shown.

Single grain YBa2Cu3O7-x (YBCO or Y123) bulk superconductors were produced by an infiltration growth process. The solid phase precursor was prepared by solid state synthesis from Y2O3 + BaCuO2 powders. The influence of the addition of Sm2O3 and YB contamination from the substrate on the microstructure and superconducting properties was analyzed. The dependences of Yb concentration on the distance from the bottom of the samples measured by energy dispersive spectroscopy microanalysis used in conjunction with scanning electron microscopy confirmed the contamination of the samples during the melting stage of the sample preparation. It is shown that the addition of Sm in low concentration and its combination with Yb from the substrate modify the coarsening of the Y211 particles as well as lead to the appearance of a secondary peak effect in the field dependences of the critical current density.

The high-temperature thermal reactivity of YBa2Cu3O7-delta (Y123) compound with Al2O3 addition (0.5-10 wt%) was investigated and the thermal processes were described. Experimentally obtained results showed that Al2O3 firstly reacted with Y123 at temperatures far below the peritectic melting point of Y123. During this solid state reaction Al partially diffused into Y123 and formed a solid solution. Also, the formation of Al-rich complex oxides, mainly with barium, and basic secondary phases as Y2BaCuO5 and CuO, was observed with increasing Al2O3 content. The formation of additional secondary phases with Al2O3 provoked their reactivity with Y123 or between themselves. After increasing the temperature of the powder mixtures above the peritectic melting point of Y123 it was found that Al was incorporated in Y123 at higher concentrations than during the solid state reaction. The reason for that could be a partial or full dissolution of Al-rich complex oxides formed at lower temperatures which in turn increased the source of Al for the incorporation in Y123. The thermal behaviour of powder mixtures was investigated with the help of simultaneous differential thermal analysis and thermogravimetry. Morphology and microstructure were examined using powder X-ray diffraction and scanning electron microscopy in combination with energy dispersive X-ray spectroscopy.

In the given contribution, the production of shape-memory glass-coated microwires based on Ni(2)FeZ (Z = Ga, Sn, Sb) and Co2Cr(GaSi) alloys is shown, focusing to their repeatable production. Such wires are characterized by monocrystalline structure along entire length. This leads to 1.5% reversible temperature shape memory effect for Ni2FeGa microwire in the as-cast state without necessity of additional thermal treatment. Moreover, well defined anisotropy results in the variation of permeability up to 550% during the phase transition. On the other hand, Co2Cr(GaSi) microwires show reversible superelastic straining up to 1.1% with a very small irreversible strain (<0.1%). (C) 2018 Elsevier B.V. All rights reserved.

Large scale production of single crystalline phase of Heusler Co2FeSi alloy microwire is reported. The long microwire (similar to 1 km) with the metallic nucleus diameter of about 2 mu m is characterized by well oriented monocrystalline structure (B2 phase, with the lattice parameter a = 5.615 angstrom). Moreover, the crystallographic direction [101] is parallel to the wire's axis along the entire length. Additionally, the wire is characterized by exhibiting a high Curie temperature (Tc > 800 K) and well-defined magnetic anisotropy mainly governed by shape. Electrical resistivity measurement reveals the exponential suppression of the electron-magnon scattering which provides strong evidence on the half-metallic behaviour of this material in the low temperature range. (C) 2018 Elsevier B.V. All rights reserved.

Barium cerate (BaCeO3) is one of the preferred additions to bulk YBa2Cu3O7 single-grain superconductors to inhibit the growth of Y2BaCuO5 particles.The present paper investigates synthesis of very fine barium cerate powder and its use in YBa2Cu3O7 bulk superconductor growth.The crystalline barium cerate was synthesized by oxalate co-precipitation from barium and cerium nitrates.X-ray diffraction in air and vacuum was performed to understand the formation of barium cerate as well as to determinate its crystal structure.Size and shape of BaCeO3 particles were studied by scanning electron microscopy.The BaCeO3 was used to grow YBa2Cu3O7 bulk superconductor.Microstructure of prepared YBa2Cu3O7 crystal shows that the barium cerate in the final product is very fine and uniformly distributed throughout the whole YBa2Cu3O7 crystal.

We report on the synthesis and characterization of a sintered bulk MgB2 material produced at an optimized sintering temperature with a varying content of carbon-encapsulated amorphous boron. A series of MgB2 bulks was prepared with 0%, 1.5%, 2.8%, 7.3%, 12% and 16.5% of carbon-encapsulated boron. In the samples with 12% of carbon-encapsulated boron, Mg and MgB2C2 formation was observed. T-c was around 38.4 K for the pure MgB2 and decreased with increasing carbon content up to 25 K for 16.5 % of carbon-encapsulated boron. The highest J(c) values of 470 kA/cm(2) and 310 kA/cm(2), in the self-field and 1 T, respectively, were achieved at 20 K, in the MgB2 sample with 1.5% of carbon-encapsulated boron. It proved that the optimized sintering conditions together with the appropriate amount of the carbon-coated boron were able to bring critical current performance of bulk MgB2 material up to the level necessary for real technical applications.

YBa2(Cu1-xLix)(3)O7-delta single-grain bulk superconductors with different Li concentrations were grown using the top-seeded melt growth process. Structural analysis of the samples and magnetisation measurements showed that substitution of the Cu atoms by the Li atoms took place in the YBa2Cu3O7-delta crystal lattice. This substitution was accompanied by the formation of effective pinning centres, which improved the pinning properties of the samples and increased the critical current density. Additional annealing and reannealing in oxygen and argon showed that the superconducting transition temperature displays substantially more suppression, when the Li-doped YBa2Cu3O7-delta samples were annealed in argon, that was associated with different distribution of the Li atoms between the CuO chains and the CuO2 planes in comparison to annealing in oxygen. Investigation of the critical current densities showed that the pinning properties of YBa2(Cu1-xLix)(3)O7-delta single-grain bulk superconductors did not depend on the arrangement of the Li atoms in the YBa2Cu3O7-delta crystal lattice. It was also observed that the crystal lattice parameters and the mean diameter of the non-superconducting Y2BaCuO5 particles systematically change with Li concentration. (C) 2017 Elsevier B.V. All rights reserved.

The microstructural analyses of YBCO bulk single-grain superconductors grown by interior seeding with taller and shorter upper pellets have shown that a suitable upper pellet height can lower the porosity in the upper part of the sample, produce a more appropriate distribution of pinning centres in the form of Y-211 particles and suppress subgrain formation with a higher crystal misalignment in the c-growth sector (c-GS), which can lead to a higher measured trapped magnetic field and a more uniform cone of the trapped-field profile. The observed bulging of the sample surface at the c-GS can be explained by the edge melt distribution model, which shows that macroscopic mass transport to the growth sector occurs with higher growth rates.

Structure of Melt-Spun Co2MnAl Heusler Alloy S. Piovarčia,∗, P. Diko, V. Kavečanský, T. Ryba, Z. Vargová and R. Varga Institute of Experimental Physics, Slovak Academy of Sciences, Watsonova 47, 040 01 Košice, Slovakia Institute of Physics, Faculty of Sciences, P.J. Šafárik University, Park Angelinum 9, 040 01 Košice, Slovakia Institute of Chemistry, Faculty of Sciences, P.J. Šafárik University, Moyzesova 11, 040 01 Košice, Slovakia