Formation of metastable Pr2Fe23B3 phase and its effect on magnetic properties in rapidly quenched Pr9Fe91-xBx nanocomposites

The formation of metastable Pr2Fe23B3 phase and. its effect on magnetic properties of melt-spun Pr9Fe91-xBx (x = 4-12) have been investigated. Thermogravimetric analysis (TGA) and X-ray diffraction (XRD) studies show that the samples consist of Pr2Fe14B and alpha-Fe phases,at low B content, and Pr2Fe14B, alpha-Fe and Fe3B at high B content. The metastable Pr2Fe23B3 phase,appears in the intermediate B content (8-12 at%). This metastable Pr2Fe23B3 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 Pr2Fe14B, alpha-Fe, and Fe3B by annealing the sample at temperature of 750 degreesC or above, leading to a more square demagnetization curve. However, B-r of the nanocomposite decreases slightly due to the excessive grain growth during high-temperature annealing.