Structure and magnetic properties of SmxCo5/α-Fe (x=0.65–1.3) prepared by mechanical milling and subsequent annealing

Abstract

Powder mixtures of ${\mathrm{Sm}}_x{\mathrm{Co}}_{\mathrm{5}}\text{\hspace{0.05em}(x=0.65–1.3)+20\hspace{0.05em}}\mathrm{wt}\mathrm{ \%}$ α-Fe were mechanically milled. Annealing these as-milled powders results in the formation of a mixture of the hard phase Sm–(Co, Fe) and the soft phase Fe–Co. For the as-milled ${\mathrm{Sm}}_{\mathrm{1}}{\mathrm{Co}}_{\mathrm{5}}\mathrm{+20 wt}\mathrm{ \%}$ α-Fe powder, the hard phase changes with the increase of annealing temperatures. The optimal maximum energy product $(\mathrm{BH}{)}_{\max }$ is obtained in the powder annealed at 550 °C for 30 min. Depending on the Sm content in the as-milled ${\mathrm{Sm}}_x{\mathrm{Co}}_{\mathrm{5}}\text{\hspace{0.05em}(x=0.65–1.3)+20\hspace{0.05em}}\mathrm{wt}\mathrm{ \%}$ α-Fe powders, the hard phases can be 1:7, 1:5, or 2:7 phase after a heat treatment at 550 °C for 30 min. The coercivity of 6.5 kOe and maximum energy product of 17.8 MGOe is achieved for the powder with $\text{x=1.0.}$ The highest coercivity of 9.67 kOe is achieved for the powder with $\text{x=1.2.}$ From the measurements of the coercivity obtained from minor hysteresis loops, it is concluded that the coercivities of this type of magnets are controlled mainly by the domain wall pinning.