Formation of metastable Pr/sub 2/Fe/sub 23/B/sub 3/ phase and its effect on magnetic properties in rapidly quenched Pr/sub 9/Fe/sub 91-x/B/sub x/ nanocomposites

The formation of metastable Pr/sub 2/Fe/sub 23/B/sub 3/ phase and its effect on magnetic properties of melt-spun Pr/sub 9/Fe/sub 91-x/B/sub x/ (x = 4-12) have been investigated. Thermogravimetric analysis (TGA) and X-ray diffraction (XRD) studies show that the samples consist of Pr/sub 2/Fe/sub 14/B and (alpha)-Fe phases at low B content, and Pr/sub 2/Fe/sub 14/B, (alpha)-Fe and Fe/sub 3/B at high B content. The metastable Pr/sub 2/Fe/sub 23/B/sub 3/ phase appears in the intermediate B content (8-12 at%). This metastable Pr/sub 2/Fe/sub 23/B/sub 3/ phase results in a poor squareness in the demagnetization curve and is detrimental to the hard magnetic properties. Transmission electron microscopy (TEM) studies reveal larger average grain sizes when the B content is at 8.5 at% or above. It is further found that this metastable phase can be transformed into Pr/sub 2/Fe/sub 14/B, (alpha)-Fe, and Fe/sub 3/B by annealing the sample at temperature of 750(degree)C or above, leading to a more square demagnetization curve. However, B/sub r/ of the nanocomposite decreases slightly due to the excessive grain growth during high-temperature annealing.