Magnetism of Rapidly Quenched Sm$_{1 - {\rm x}}$Zr$_{{\rm x}}$Co$_{5}$ Nanocrystalline Materials

The effect of Zr addition on nanostructure and magnetic properties in nanocrystalline Sm$_{1 - {\rm x}}$Zr$_{{\rm x}}$Co$_{5}$ $({\rm x} = 0-0.6)$ has been investigated. (Sm, Zr)Co $_{5}$ with the CaCu $_{5}$ structure was synthesized by melt spinning. The lattice parameters a and b decrease with x, whereas c increases. Thus, the unit cell volume of (Sm, Zr)Co$_{5}$ shrinks because the smaller Zr atoms occupy the sites of the larger Sm atoms. Zr addition decreases the grain size and induces the formation of planar defects. The coercivity decreases with x, due to weakening of magnetocrystalline anisotropy energy and effective intergrain exchange coupling. A very high coercivity of 39 kOe and energy product of 13.9 MGOe are obtained for ${\rm x} = 0$. The remanence of (Sm, Zr)Co $_{5}$ increases with x. For ${\rm x} \leq 0.4$, the energy product slightly decreases with x. The results show that 40% of the Sm can be replaced by the less expensive Zr, with an energy-product reduction of only 10%. In addition, the planar defects are responsible for the change of coercivity mechanism from the nucleation-type of reverse domain for the ${\rm x} = 0$ to the pinning-type of domain wall for the ${\rm x} = 0.4$.