Magnetic properties, phase evolution, coercivity mechanism, and aftereffect of PrFeB-type nanocomposite ribbons

• Main Authors: H. W. Chang, 張晃暐
• Other Authors: W. C. Chang
• Format: Others
• Language: zh-TW
• Published: 2004
• Online Access: http://ndltd.ncl.edu.tw/handle/55311899467661245718

博士 === 國立中正大學 === 物理系 === 92 === Abstract Magnetic properties and phase evolution of PrFeB-type nanocomposites of Pr10Fe90-xBx (x = 5.88-11.5), PryFe90-yB10 (y = 8-11.76), Pr9.5Fe78.5M2B10, Pr8.5Fe79.5M2B10, and Pr2(Fe0.975M0.025)23B3 ribbons have been investigated. In addition, the coercivity mechanism and aftereffect of the above ribbons were also studied. Major conclusions are listed as follows: 1. Magnetic properties of PrFeB nanocomposites are mainly determined by both the volume fraction of magnetically soft and hard phases and the distribution of grain size in the ribbons. As the rare earth content is lowered to below 9 at％ at boron content of 10 at％ in PrFeB nanocomposites, metastable R2Fe23B3 phase appears, with reducing the volume fraction of R2Fe14B, and deteriorates the magnetic properties drastically. A slight substitution of the refractory elements (Cr, Nb, V, Ti and Zr) for Fe near the Pr2Fe23B3 (Pr9.5Fe78.5M2B10 and Pr8.5Fe79.5M2B10) and in Pr2Fe23B3 ribbons can suppress the formation of metastable 2:23:3 and Fe3B phases effectively and lead to the presence of large amount of 2:14:1 and α-Fe phases of fine grain size (< 30 nm). As a result, magnetic properties of these ribbons are improved remarkably. The optimal magnetic properties of Br = 9.6 kG, iHc = 8.5 kOe and (BH)max = 17.8 MGOe are achieved in Pr8.5Fe79.5Ti2B10 and the highest coercivity of iHc = 13.2 kOe (Br = 9.0 kG and (BH)max = 16.9 MGOe) are obtained in Pr9.5Fe78.5Nb2B10. Furthermore, Br = 9.9 kG, iHc = 5.7 kOe and (BH)max = 15.0 MGOe can be also obtained in Pr2(Fe0.975Ti0.025)23B3. Most importantly, the above results prove that adopting PrFeMB type nanocomposites can expand the applicable composition range as comparison with those of NdFeB-type nanocomposites for making rare earth bonded magnets. 2. The coercivity of all samples in this research is mainly dominated by both nucleation and weak pinning effect. 3. The activation volume of PrFeB nanocomposites tend to enhance with the increment of magnetically soft phases content. The relationship of activation volume (V) and coercivity follows log (V-1) = 1.51*log (Hc) + 11.72, i.e: V ~ Hc-1.51. It is presumably arisen from the higher anisotropy field of Pr2Fe14B phase. 4. The optimal magnetic properties of Br = 9.9 kG, iHc = 8.0 kOe and (BH)max = 18.7 MGOe are achieved in (Pr0.75Nd0.25)8.5Fe79.5Ti2B10 and the highest coercivity of iHc = 13.2 kOe (Br = 9.0 kG and (BH)max = 16.9 MGOe) are obtained in Pr9.5Fe78.5Nb2B10. They are quite appropriate for making bonded magnets with multiple magnetization and higher temperature application, respectively. Meanwhile, they are new record of the ribbons near the composition of 2:23:3 ever reported.