Effect of Zr substitution for rare earth on microstructure and magnetic properties of melt-spun (Nd0.75Pr0.25)12.5−xZrxFe82B5.5 (x=0–3) ribbons

Abstract

The effect of Zr substitution for rare earth on the microstructure and hard magnetic properties of melt-spun composition of (Nd0.75Pr0.25)12.5−xZrxFe82B5.5 (x=0–3) has been investigated. It has been found that the coercivity decreases monotonically with the increasing Zr content, from 12.0 kOe at x=0 to 10.1 kOe with x=3. Unlike the coercivity, the remanence first increased with Zr substitution, from 8.65 up to 8.93 kG at x=2, and then decreased with further Zr substitution. The energy product behaved similarly, increasing from 15.7 MGOe to a maximum of 16.5 MGOe at x=2. X-ray diffraction (XRD), transmission electron microscope (TEM), and thermogravimetric analyzer studies have shown that all the samples were primarily composed of the single R2Fe14B phase. No additional phase was observed with Zr substitution. The lattice constants and the Curie temperature of the 2:14:1 phase were found to decrease monotonically with increasing Zr content, suggesting that all the Zr is situated into the 2:14:1 matrix, occupying the rare earth sites. TEM and XRD studies also revealed a significant grain size reduction with Zr substitution. The average grain size was reduced from approximately 40 nm in Zr-free samples to about 20 nm in samples with x=2. The observed change in magnetic properties with Zr substitution is explained by the grain size reduction.