Research Digest 29The effect of V on the phase stability and intrinsic magnetic properties of SmFe12-xVx (0 ≤ x ≤ 1.9) thin films, and bulk SmFe12-xVx (x = 1.5 and 2) are investigated. It is found that V help to stabilize the ThMn12-type phase by decreasing the lattice parameters c and the c/a ratio up to its solid solubility limit x = 1.4. Above this limit, the formation of Sm-rich phase has been observed in the microstructure. Interestingly, Curie temperature (Tc) and anisotropy field (μ0Ha) do not exhibit the same trend with the magnetization (μ0Ms) where increasing V enhances the two quantities while decreasing the magnetization. The Tc increase from 533 K for x = 0 up to 660 K for x =1 agrees with first principles calculation and it is related with the strengthening of the effect of Fe-V coupling along with its surrounding Fe-Fe couplings (Fig.5). This particular Tc enhancement effect didn’t observe experimentally for the other phase stabilizer elements such as Ti,W,Si.. etc. Preservation of room temperature anisotropy field between 10 - 12 T is confirmed by micromagnetic simulation. This study demonstrates that V-substituted compounds with 7 at. % phase stabilizers have more merit than Ti-substituted ones for the development of high-performance magnet with better extrinsic magnetic properties [1]. We investigated the phase equilibrium in the Sm-Fe-V system, so that we can establish an optimum composition range to develop high coercivity SmFe12-based permanent magnets. For this purpose, we growth epitaxially thin films with a nominal composition of SmxFe92.3-yVy (x = 7.7 and y = 0, 3.4, 5.4, 7.7, 10.8, 14.6, 18.5, 20, 27, and 30), Sm-rich Sm10Fe90-yVy (x = 10 and y = 15, 17, 18, 20, and 21.5), V-rich SmxFe80-xV20 (x = 5.7, 6, 6.7, 7, 7.7, 8, and 9; y = 20), and SmxFe85-xV15 (x = 8, 10, and 15; y = 15). In addition to the 1:12/Sm-rich liquid-phase equilibrium, an additional V-rich liquid phase is found in the Sm-Fe-V phase diagram for V contents between 19 to 35 at.%. The equilibrium between the 1:12 phase and the two liquid phases is computationally modeled for Sm-Fe-V metastable phase diagram (Fig. 1). This is experimentally confirmed by analyzing the microstructure of the Sm8Fe72V20 thin film, where anisotropic columnar 1:12 grains are enveloped with predominantly V-rich phases along with some Sm-rich intergranular phases. This microstructure produces a coercivity µ0Hc=0.9 T with strong perpendicular anisotropy, µ0Ha=10 T [2] Fig. 1. Sm–Fe–V phase diagram at 1500 K with associated Hc.References1) P. Tozman, T. Fukazawa, D. Ogawa, H. Sepehri-Amin, A. Bolyachkin, T. Miyake, S. Hirosawa, K. Hono, Y. K. Takahashi, Acta Mater., 232, 117928 (2022).2) P. Tozman, H. Sepehri-Amin, T. Abe, K. Hono, Y.K. Takahashi, Acta Mater., 258, 119197 (2022).1. Outline of ResearchPermanent magnets are used widely in green energy technologies such as electric vehicles and wind turbines to reduce the global CO2 emissions. So far, (Nd,Dy)-Fe-B sintered magnets have been the material of choice for these applications. However, limited natural rare earth resources (especially Nd and Dy) with geopolitical issues and increasing demand for a type of magnet containing these elements cannot guarantee a sustainable permanent magnet industry. To solve this problem, SmFe12-based compounds are considered as a potential candidate for the next generation high performance permanent magnets, owning to their small usage of abundant rare-earth elements and superior intrinsic magnetic properties than that of Nd2Fe14B at elevated operation temperatures. However, realizing coercivity in these compounds is the main problem for their practical application, due to their phase instability and their inability to achieve the desired microstructure as a bulk. In this project, I seek the way how to overcome the phase stability problem while maintaining the high magnetization and exploring the secondary phases which are beneficial for coercivity development. 2. Research ActivitiesA Search for a Novel Alloy for High Performance Permanent Magnet ApplicationsPelin TOZMAN
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