Fabrication and magnetic properties of Iron-rich intermetallic compounds with ThMn<SUB>12</SUB> structure

다국어 초록 (Multilingual Abstract)

Rare-earth intermetallic compounds of R(Fe,M)12 (R = rare earth elements, M = transition metals) with ThMn12 structure have been known to be promising permanent magnetic materials since the 1980s. Recently, increasing rare earth price has pushed the industry to seek ways to reduce the R-content in the hard magnetic materials. In case, strong magnets with the ThMn12 type of structure received much attention. However, during the several tens of years, the research about ThMn12 magnetic materials was not made a breakthrough. As a turning point of the ThMn12-type Fe-rich compounds research, ThMn12-type Sm(Fe1-xCox)12 compound films with a saturation magnetization of 1.78 T, an anisotropy field of 12 T, and a Curie temperature of 586 °C, all of which are superior to those for Nd₂Fe14B, were successfully produced. However, it still has difficulty in stabilizing the unstable ThMn12 phase in magnetic powders and bulks. In previous research, the ThMn12 structure is also unstable and partial Fe atoms must be substituted with phase stabilizing element(s), such as Ti, V, Cr, Mn, Mo, W, Al, and Si, which results in magnetization reduction. So, decreasing magnetization or coercivity with the non-magnetic elements substitution is a new challenge for the ThMn12-type Sm(Fe1-xCox)12 compound research. Therefore, we have developed a new fabrication method to produce a high-density Sm(Fe0.8Co0.2)11Ti bulk with high purity and magnetic properties and investigated Si substitution or doping effects on this work"s magnetic and physical properties.
The purity of the hard magnetic ThMn12 phase in the bulk magnet reached higher than 97 wt.%. The remanent magnetization and maximum energy product of the prepared Sm(Fe0.8Co0.2)11Ti bulk reached high values of 96.0 emu/g and 12.22 MGOe, respectively. The phase transformation behavior from amorphous to ThMn12 phase during heat treatment was systematically investigated by transmission electron microscopy. The magnetic properties and grain sizes of Sm(Fe0.8Co0.2)11Ti bulk magnets with different annealing times were shown in Fig. 1 (a). To investigate the effect of substituted elements in the ThMn12-type Fe-rich compounds and compare with the Ti substitution, Si was selected to dop into the ThMn12-type Fe-rich compounds. Sm(Fe0.8Co0.2)10Si₂ and Sm(Fe0.8Co0.2)11Ti+Six (x = 0, 0.5, and 1) ribbons were produced using a melt spinning method. The magnetic properties of the Sm(Fe0.8Co0.2)10Si₂ ribbons with different melt spinning speeds and the Sm(Fe0.8Co0.2)11Ti+Six ribbons with melt spinning speed of 39 m/s are shown in Fig. 1 (b). The maximum coercivity of the Sm(Fe0.8Co0.2)10Si₂ and Sm(Fe0.8Co0.2)11Ti+Six ribbons reached 1745 and 3140 Oe, respectively. The details of the fabrication procedure, microstructure, and magnetic properties of as mentioned compounds will be discussed.
〈그림 본문참조〉