关键词: Cu addition, nanocomposite, magnetic properties, energy product, remanence

Abstract: The melt-spun ribbons of nominal composition Pr$_{9}$Fe$_{84.2-x}$B$_{6.2}$P$_{0.3}$Zr$_{0.3}$Cu$_{x}$ ($x=0$, 0.5, 1, 2) were prepared at wheel speeds of 21 m$\cdot$s$^{-1}$, 27 m$\cdot$s$^{-1}$, 30 m$\cdot$s$^{-1}$, and 33 m$\cdot$s$^{-1}$. The XRD patterns show that as the wheel speed increases, the crystallinity of the 2:14:1 hard phase decreases, while that of the $\alpha $-Fe soft phase increases. The $(BH)_{\rm max}$, remanence, and coercivity are improved from 63 kJ$\cdot$m$^{-3}$, 0.85 T, and 515 kA$\cdot$m$^{-1}$ for the Cu-free ribbons to 171 kJ$\cdot$m$^{-3}$, 1.08 T, and 684 kA$\cdot$m$^{-1}$ with $x=0.5$. The high squareness ratio of $J_{\rm r}/J_{\rm s} \sim 0.82$ at 0.5 at.% Cu (27 m$\cdot$s$^{-1}$) indicates strong exchange coupling due to small grain sizes of 15 nm and 30 nm for soft and hard magnetic phases, respectively. The SEM images revealed smooth morphology and uniform element distribution at 0.5 at.% Cu (27 m$\cdot$s$^{-1}$), contributing to the high magnetic properties. The low recoil permeability ($\mu_{\rm rec}$) value of $5.466\times {10}^{-4}$ T/kA$\cdot$m$^{-1}$ to $1.970\times {10}^{-4}$ T/kA$\cdot$m$^{-1}$ confirms the strong exchange coupling with $x=0.5$ (27 m$\cdot$s$^{-1}$). The initial magnetization curves show that the coercivity mechanism of the Cu-free alloy evolves from the nucleation of the reverse domain to the domain wall pinning as the wheel speed increases, resulting in a high coercivity value of 818 kA$\cdot$m$^{-1}$ (33 m$\cdot$s$^{-1}$). Conversely, for the Cu-added alloy, the coercivity mechanism changes from pinning to the nucleation of the reverse domain from low to high wheel speed.

Key words: Cu addition, nanocomposite, magnetic properties, energy product, remanence