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The effect of quench rate and Zr content on nanostructure and magnetic properties of melt-spun ZrxCo100−x (x = 16-21) is investigated. High quench rate favors the formation of rhombohedral Zr2Co11, which is the hard phase. The coercivity increases with an increase in quench rate. Zr addition in limited amounts decreases the grain size of magnetic phases, which may promote the effective exchange coupling of soft magnetic phases. Therefore, coercivity and maximum energy product of Zr2Co11-based materials are significantly enhanced. The best magnetic properties, iHc = 3.0 kOe and (BH)max = 4.6 MG Oe, which are the highest reported values among Co-Zr binary alloys, are achieved for x = 18. The temperature coefficients of coercivity and remanence between 100 and 380 K are −0.05% K −1 , comparable to those of alnico magnet.

A nonequilibrium rapid-quenching method has been used to fabricate NiMnIn and NiMnGa alloys that are chemically and morphologically similar but crystallographically and physically very different. NiMnGa crystallizes in a Ni 2 In-type hexagonal structure, whereas NiMnIn is a cubic Heusler alloy. Both alloys yield a topological Hall effect contribution corresponding to bubble-type skyrmion spin structures, but it occurs in much lower magnetic fields in NiMnIn as compared to NiMnGa. The effect is unrelated to net Dzyaloshinskii-Moriya interactions, which are absent in both alloys due to their inversion-symmetric crystal structures. Based on magnetic-force microscopy, we explain the difference between the two alloys by magnetocrystalline anisotropy and uniaxial and cubic anisotropies yielding full-fledged and reduced topological Hall effects, respectively. Since NiMnIn involves small magnetic fields (0.02-0.3 kOe) at and above room temperature, it is of potential interest in spin electronics.

Magnets with chiral crystal structures and helical spin structures have recently attracted much attention as potential spin-electronics materials, but their relatively low magnetic-ordering temperatures are a disadvantage. While cobalt has long been recognized as an element that promotes high-temperature magnetic ordering, most Co-rich alloys are achiral and exhibit collinear rather than helimagnetic order. Crystallographically, the B20-ordered compound CoSi is an exception due to its chiral structure, but it does not exhibit any kind of magnetic order. Here, we use nonequilibrium processing to produce B20-ordered Co 1þx Si 1−x with a maximum Co solubility of x ¼ 0.043. Above a critical excess-Co content (x c ¼ 0.028), the alloys are magnetically ordered, and for x ¼ 0.043, a critical temperature T c ¼ 328 K is obtained, the highest among all B20-type magnets. The crystal structure of the alloy supports spin spirals caused by Dzyaloshinskii-Moriya interactions, and from magnetic measurements we estimate that the spirals have a periodicity of about 17 nm. Our density-functional calculations explain the combination of high magneticordering temperature and short periodicity in terms of a quantum phase transition where excess-cobalt spins are coupled through the host matrix.

The Mo-content dependence of structure and magnetic properties of ( , 2, 3, 4, 5) nanocrystalline materials has been studied. The samples consist of hard-magnetic and soft-magnetic Co phases. The substitution of Mo for Co restrains the formation of Co, raises the content of , and increases the mean grain size of . Therefore, the coercive force of the sample increases with x. A coercive force of 7.9 kOe, which is a highest value reported among Zr-Co alloys, was achieved for . The anisotropy field of remains almost unchanged with increasing Mo content.