The effect of addition Cu on the appearance of formation ability and high coercivity for Nd-Fe metastable phase by using short drop tube process

We have previously reported the undercooling solidification behavior and high coercivity(Hc) of the Nd-Fe-based metastable phase using various containerless processes. However, the mechanism of high coercivity of the metastable phase is unclear. In this study, we have intended to examine the effect of Cu addition on the formation and high coercivity of Nd-Fe-based metastable phase using close to the stoichiometric composition of the Nd₆₀Fe₄₀ binary alloy. In addition, we have analyzed the relationship between high coercivity and the 3d-4f valence electron state by X-ray photoelectron spectroscopy (XPS) analysis. The Nd-Fe-Cu ternary particle samples were found to solidify by the drop tube process. The coercivity which was 5.8×10³ Oe, increased by about two fold after Cu addition. X-ray diffraction (XRD) results showed that crystallization of the a-Nd phase was markedly suppressed in the Nd₆₀Fe₂₅Cu₁₅ ternary particle samples. This is attributed to the increased production of the metastable phase by addition of Cu. The effectiveness of Cu addition on the formation of the metastable phase is suggested for this purpose. Using energy-dispersive X-ray analysis (EDS), the Nd-Fe-Cu ternary metastable phase composition ratio was found to be very similar to that of the Nd₆₀Fe₂₅Cu₁₅ ternary based material (Nd:Fe:Cu=12:5:3). From the XPS result for the Nd₆₀Fe₄₀ binary and Nd₆₀Fe₂₅Cu₁₅ ternary particle samples, the 3d-4f bonding energy shifted to lower energy by Cu addition. Therefore, it is suggested that high coercivity depends on the increase of the 3d-4f electron bonding energy strength by the addition of Cu.