Phase composition and nanostructure of Zr2Co11-based alloys

Abstract

The effect of Mo addition on phase composition and nanostructure of nanocrystalline Zr16Co84−xMox (x = 0–2.0) melt spun at 55 m/s has been investigated. All the ribbons consist mainly of a hard magnetic Zr2Co11 phase with rhombohedral crystal structure but also contain minor amounts of soft-magnetic phases. The increase in cell volume on alloying suggests that Mo mainly enters the rhombohedral Zr2Co11 structure and occupies the Co site. Mo addition promotes the formation of the hard magnetic phase and increases its volume fraction. The mean grain size of the hard magnetic phase remains almost unchanged with the increase of Mo content. But the average grain size of the soft magnetic phase decreases from about 200 nm to 50 nm. This promotes the exchange coupling of the hard and soft magnetic phases and thus leads to a significant increase in coercivity and isotropic energy product, from 0.6 kOe and 0.5 MGOe for x = 0 to 2.9 kOe and 4.2 MGOe for x = 1.5.

Effect of boron doping on nanostructure and magnetism of rapidly quenched Zr2Co11-based alloys

“…Metallic additives such as Ti, Si or Mo facilitate the formation of the hard-magnetic phase and decreases both the mean grain size and the amount of the soft Co phase. 5,[10][11][12] The addition of Si and B has a similar effect. 3 In particular, boron addition has been found to increase the coercivity of rapidly quenched Zr-Co materials, 13,14 but it is unclear how B addition affects the phase components and structural properties.…”

“…Rhombohedral Zr 2 Co 11 can therefore be produced by quenching the molten mixture so long as the quench rate is sufficiently high. 5,[7][8][9] The higher the quench rate, the larger the content of rhombohedral Zr 2 Co 11 and the more refined the nanostructure, both enhancing the coercivity. 3,8 However, binary Zr-Co ribbons have relatively low coercivities.…”

“…[1][2][3][4][5] Alloys with the approximate stoichiometry Zr 2 Co 11 crystallize in cubic, orthorhombic, and rhombohedral structures, but only the rhombohedral phase, which is predicted to be metastable by formation-energy calculations, leads to significant coercivity. 3,5,6 The structures are basically dense-packed, with structural motifs reminiscent of that in SmCo 5 . 6 Rhombohedral Zr 2 Co 11 is a high-temperature phase, whereas the orthorhombic phase is more stable at low temperatures.…”

Magnetic Force Microscopy Study of Zr2Co11‐Based Nanocrystalline Materials: Effect of Mo Addition

“…The coercivity, anisotropy field, and maximum energy product are found to strongly depend on the Mo content. As discussed by Jin et al [9], Mo addition increases the volume fraction of the hard magnetic phase, decreases the grain size of soft magnetic phase, and promotes the interphase exchange coupling action between hard magnetic and soft magnetic grains. The magnetocrystalline anisotropy field = 2 / 0 and the spontaneous magnetization the hysteresis loops using the law of approach to saturation method [12].…”

“…Nanocrystalline Zr 2 Co 11 -based materials are promising candidates for the development of rare-earth-free permanent magnets due to their good intrinsic magnetic properties with strong uniaxial anisotropy (11 Merg cm −3 ) and high Curie temperature (>500 ∘ C) [1][2][3][4][5][6]. The rhombohedral Zr 2 Co 11 phase is identified to be responsible for the magnetic hardness in rapidly quenched alloys as discussed elsewhere [6][7][8][9]. The coercivity and maximum energy product of Zr 2 Co 11 -based nanocrystalline materials also were efficiently enhanced by the introduction of Mo element [10,11].…”