Novel hard-magnetic compound with Zr11.5Fe53Si35.5 composition

Abstract

Demand for high performance rare earth (RE) permanent magnet has been increased due to recent progress of electric vehicles or other power electric applications. Meanwhile, development of RE less or RE free magnet material is also important to deal with supply risk in RE element resource. In Zr-Fe-Si ternary system, many ternary phases have been reported [1-3], including hard magnetic compounds such as ZrFe10Si2 [2] of ThMn12 type and Laves type Zr(Fe, Si)2 [3]. In this work, to discover a new hard magnetic phase of RE free, we performed material search experiment in Zr-Fe-Si ternary system. Bulk alloy samples with various composition in Zr-Fe-Si system were prepared by arc melting under high purity Ar atmosphere. The examined composition was in range of Zr: 8~23 at%, Fe: 35~80 at% and Si: 5~55 at%. Then, the prepared alloys were annealed at 1050 oC under 200 Pa during Ar flow atmosphere. Compositions and crystal structures of formed phases in the alloys were analysed by SEM-EDX and XRD. Magnetization curves of the alloys was measured by using superconducting VSM, and Curie temperatures (Tc) of ferromagnetic phases included in the alloys were evaluated by thermo-magnetic analysis (TMA). We also observed magnetic domains in the polished surfaces of the bulk alloy samples using magneto-optical polar Kerr microscope to find hard magnetic phases. From the experiments, we found a certain ferromagnetic phase with Zr11.5Fe53Si35.5 composition and Tc of 260 oC (called “phase X”). This phase showed maze domain structure in the polar Kerr microscope images, which indicates that “phase X” is a hard magnetic phase. Moreover, all alloy samples including “phase X” showed magnetic hysteresis loops with coercivities (HcJ) at room temperature without any microstructural controlling. The highest values of HcJ was 338 kA/m among the present samples. On the other hand, the saturation magnetization was estimated as ~24 Am2/kg. By the XRD measurements and the composition analysis, we could not identified “Phase X” as any already-known ternary phase in Zr-Fe-Si system such as ZrFe10Si2, Laves type Zr(Fe, Si)2, ZrFe4Si2, and (Zr,Fe)5Si3. Therefore, we conclude “phase X” is a novel compound of hard magnetic phase. [1] C.P. Wang et. al., Journal of Phase Equilibria and Diffusion, 34, 4, 277 (2013). [2] A.M. Gabay et. al., Journal of Alloys and Compounds, 657, 5, 133 (2016). [3] D. Goll et al, Physica Status Solidi - Rapid Research Letter, 12, 1700221 (2017).