We studied the effect of annealing on magnetic properties and structure of Heusler-type NiMnGa glass-covered microwires with a metallic nucleus diameter of about 22 μm prepared using the Taylor–Ulitovsky method. The as-prepared NiMnGa glass-covered microwires do not present ferromagnetic order at room temperature. Magnetization curves of the as-prepared samples do not present either saturation or coercivity at temperatures above 5 K. After annealing of the microwires, a ferromagnetic ordering is obtained with a Curie temperature of about 300 K which is beneficial for magnetic solid state refrigeration. The hysteresis observed on temperature dependence of magnetization in annealed samples and magnetic softening at about 260 K has been interpreted as the first-order phase transformation. Observed changes have been discussed considering internal stress relaxation after annealing, nanocrystalline structure of the as-prepared and annealed samples, recrystallization process and magnetic ordering of phases identified in the as-prepared sample and appearing under recrystallization. Existence of insulating and flexible glass-coating is beneficial for improvement of mechanical properties but the glass coating considerably affects magnetic properties of NiMnGa microwires. Therefore special attention must be paid to annealing conditions for realization of martensitic transformation.

Martensitic transformation and magnetic entropy change in Co substituted Ni50Mn35−xCoxSn15 (x = 0, 1.0, 1.5, 2.0, and 3.0) Heusler alloys have been investigated by X-ray powder diffraction analysis, differential scanning calorimetry, and magnetic measurements. X-ray diffraction analysis reveals that the Ni50Mn35−xCoxSn15 alloys have L21 Heusler structure at room temperature. The phase decomposition of the sample with x = 3.0, after annealing 48 h at 1173 K, is confirmed by both X-ray powder diffraction analysis and energy-dispersive x-ray spectroscopy in scanning electron microscopy. With the increase of the Co content from 0 to 2.0, the martensitic transformation temperature TM increases from 185 to 245 K, which is in good agreement with the rule of valence electron concentration e/a-dependence of TM. The magnetic entropy change ∆SM is investigated in the vicinity of the martensitic transformation.

High-throughput synthesis and characterization techniques have been effective in discovering new materials and performing rapid mapping of phase diagrams. The application of the combinatorial strategy to explore doped transition-metal oxides has led to the discovery of a transparent room-temperature ferromagnetic oxide in Co-doped anatase TiO2. The discovery has triggered a wave of studies into other metal oxide systems in pursuit of diluted magnetic semiconductors. In this article, we describe recent combinatorial studies of magnetic transition-metal oxides, germanium-based magnetic semiconductors, and Heusler alloys.