Iron-rich 2:17-type Sm-Co magnets are important for their potential to achieve high coercivity and maximum magnetic energy product. But the evolution of phase structure, which determines magnetic properties, remains an unsolved issue. In this study, the phase constitution and microstructure of solution-treated 2:17-type Sm-Co alloys are studied. The increase of Fe content promotes the ordering transformation from the 1:7H phase to partially ordered 2:17R and lamellar Zr-rich 1:3R phase. This ordering transformation is mainly due to the competitive atoms occupation of Zr, Fe and Sm in the 1:7H phase. To ease this competition, we modify Sm content in iron-rich 2:17-type Sm-Co magnets. Different solution precursors and corresponding cellular structures are observed. Solution precursor with 1:7H, partially ordered 2:17R, 2:17H and 1:3R phase evolves into uneven and incomplete cellular structures, while solution precursor with partially ordered 2:17R phase forms larger cell size with less lamellar phase, thus poor coercivity and magnetic energy product. However, solution precursors with single 1:7H phase evolve into uniform cellular structures and perform high coercivity and magnetic energy product. Our results indicate if a single 1:7H phase could be obtained in solution-treated 2:17-type Sm-Co magnets with higher iron content, much higher magnetic properties could be achieved.

The $\text{Sm}{\left(\text{Co},\text{Zr}\right)}_7/\alpha \text{-}\left(\text{Fe}–\text{Co}\right)$ nanocomposite permanent magnets are produced by mechanical alloying and subsequent annealing. The soft magnetic phases were introduced by two different processes. In the first process, the crushed as-cast ${\text{SmCo}}_{6.8}{\text{Zr}}_{0.2}$ powders were blended and milled with different weight percent of fine iron powders $\left(\text{SCZ}+\text{Fe}\right)$ and in the second process, the crushed as-cast ${\left({\text{SmCo}}_{6.8}{\text{Zr}}_{0.2}\right)}_{1-\text{x}}{\text{Fe}}_{\text{x}}$ $\left(\text{x}=0,0.1,0.25,0.5,0.75\right)$ powders (SCZF) were milled directly. XRD analysis showed that the phase structure of annealed $\text{SCZ}+\text{Fe}$ are consisted of ${\text{SmCo}}_7$ phase and $\alpha \text{-}\left(\text{Fe},\text{Co}\right)$ phase, while the composites of annealed SCZF are composed of $\alpha \text{-}\left(\text{Fe},\text{Co}\right)$ and SmCo hard phases that varied with different Fe content. The best energy product of the annealed SCZF and $\text{SCZ}+\text{Fe}$ are 11.3 MGOe (SCZF-3) and 10 MGOe $\left(\text{SCZ}+\text{Fe-}1\right)$ , respectively, resulting from the very strong exchange coupling between the hard phase and the soft phase. According to the Henkel-plots of SCZF-3 and $\text{SCZ}+\text{Fe-}1$ , a stronger intergrain exchange coupling effect was observed in SCZF-3 sample. The irreversible nucleation fields of SCZF-3 and $\text{SCZ}+\text{Fe-}1$ are also studied in detail.

In this study, the effects of Y₂O₃ addition on the magnetic properties, microstructure and magnetization reversal behavior of Sm(Co_0.79Fe_0.09Cu_0.09Zr_0.03)_7.68 magnet were investigated. By addition of Y₂O₃, the coercivity was increased from 21.34 kOe to 27.42 kOe at 300 K and from 5.14 kOe to 6.27 kOe at 823 K. A magnet with a maximum magnetic energy product of 9.86 MGOe at 823 K was obtained. With the interdiffusion of Y and Sm after appropriate addition, the Cu content within the cell boundary phase close to the oxide was detected to be nearly twice as high as that away from the oxide. We report for the first time that a collection of lamellar phases were formed on both sides of the inserted oxide, providing a strong pinning field against magnetic domain wall motion based on in-situ Lorentz TEM observation. Furthermore, the ordering process of the original magnet was delayed after Y₂O₃ addition, resulting in the refinement of cellular structure, which can also enhance the domain wall pinning ability of cellular structures based on micromagnetic simulation. However, excessive addition of Y₂O₃ led to large Cu-rich phase and Zr-rich impurity phase precipitated at the edge of the oxide, resulting in the destruction of cellular structures and a significant reduction in coercivity. This study provides a new technical approach to regulate the microstructure of Sm₂Co₁₇ type magnets. Addition of Y₂O₃ is expected to play a significant role in improvement of high temperature magnetic properties.