Effect Of Additive Alloy Elements On Coercivity Of Nd₂Fe₁₄B/α-Fe Nanocomposite Magnets

Nanocomposite exchange coupled magnets consisting of a fine mixture of hard- and soft-magnetic phases have attracted much interest because of their potential applications in exhibiting a high maximum energy product. However, there is still a discrepancy between patically obtained and predicted maximum energy product in nanocomposite magnets because of the difficulty in obtaining the optimum microstructure employed in theoretical models. As one of the significant parameters, a low coercivity limits the realization of high-energy product in nanocomposite magnets, however, there is a low loercivity both in single-phase magnets and nanocomposite magnets. Numerous studies show that a small amount of alloying elements can improve the microstructure and enhance the coercivity of Nd2Fe14B/α-Fe nanocomposite magnets. In this paper, Nd2Fe14B/α-Fe nanocomposite magnets were prepared by melt-spinning and hot-pressing. The magnetic properties of the Nd2Fe14B/α-Fe nanocomposite magnets were studied by employing a vibrating sample magnetometer(VSM) and the microstructure of the magnets was studied by using X-ray diffraction(XRD) measurements.In this paper, Nd2Fe14B/α-Fe nanocomposite magnets were prepared by melt-spinning. The elements of Ti and Nb segregate at grain boundary of Nd9Fe85B6 magnet. The grain size of soft-magnetic phase and hard-magnetic phase 16.5 nm and 29.7nm reduce to 15.6 nm and 23.6 nm, respectively. The additive of Ti and Nb promote the formation of an interfacial amorphous phase in Nd2Fe14B/α-Fe nanocomposite magnets, which improve the interface structure, then enhance the domain-wall-pinning strength, strengthen the exchange-coupling interaction. Thus a high-energy product of(BH)max=23.7 MGOe and a large coercivity of Hci=7.8 kOe were obtained in Nd9Fe83.2Ti0.8Nb1B6 magnet, showing enhanced magnetic properties with increases by 8% in(BH)max, 32% in Hci as compared to the Nd9Fe85B6 magnet.The bulk Nd2Fe14B/α-Fe nanocomposite magnets which contain low-melting alloys Nd70Cu30 were prepared by hot-press processing. The Nd70Cu30 alloy was diffused in Nd2Fe14B/α-Fe nanocomposite magnets, which improve the interface structure, after annealing process in vacuum. As we can see, the coercivity was increased with the content of Nd70Cu30. The coercivity of sample with 6wt% Nd70Cu30 was increased from 7.7 kOe to 8.8 kOe after annealing at high temperature in short time. The coercivity of sample with 6wt% Nd70Cu30 was increased from 7.8 kOe to 9.4 kOe after enough annealling process at low temperature.