The role of combined addition of Ti and B in magnetic hardening of devitrified Pr 2Fe 14B/(Fe 3B,α-Fe) nanocomposite magnets

Abstract

Pr 2Fe 14B/(Fe 3B,α-Fe) nanocomposite magnets with high coercivity have been prepared by devitrification of Pr 9Fe 88.5-xTi 2.5B x(x = 7, 9, 11, 13, and 15) amorphous ribbons. Similar to Zr and Nb, Ti Substitutes rare earth sites and participates in forming the (Pr,Ti) 2Fe 14B phase. The increasing amount of nonmagnetic TiB 2 with increasing x in the nanocomposite magnets may precipitate along the grain boundaries and refine the microstructure by inhibiting the grain growth, and results in a continuous increase of coercivity. It also leads to an increase of the fraction of soft phases in the nanocomposites, which enhances the remanence. The squareness of the demagnetization curves is also improved by appropriate B addition. As a result, the energy product attains a maximum value of 129.6 kJ/m 3 for x = 13. A more obvious shoulder and significantly enhanced coercivity (2424 kA/m) in the hysteresis curves at 70 K was observed for the sample with x = 15 in comparison with the ribbon with x = 7. This further demonstrates that B addition promotes the formation of TiB 2 and the Fe 3B soft phase in good agreement with XRD results. Accordingly, the introduction of a proper amount of nonmagnetic phases can enhance the magnetic properties of the nanocomposite magnets. © 2008 WILEY-VCH Verlag GmbH & Co. KGaA.