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Ganghwi Kim,Dae-Han Jung,Suyeong Jeong,Namkyu Kim,Ki-Suk Lee 한국자기학회 2021 한국자기학회 학술연구발표회 논문개요집 Vol.31 No.1
SmFe<sub>12</sub>–based compounds have been considered as a good candidate for a future permanent magnet without the critical elements such as Nd or Dy [1]. One of the most challenging issues to achieve a high-performance permanent magnet is that forming an appropriate grain boundary phase is suppressed in SmFe<sub>12</sub>–based magnets [2,3]. Therefore, grain boundary effects to enhance magnetic properties such as remanence and coercivity rarely occur, and practical magnetic properties are assessed as relatively low. To overcome this, adding impurities can reinforce the performance of a permanent magnet by inducing the formation of the grain boundary phase. For example, Cu – Ga grain boundary infiltration [2] and co-sputtering of B [3] can cause the grain boundary phase formation. Especially, doping of B induces amorphous ferromagnetic grain boundary creation, which results in a significant improvement of coercivity and remanence [3]. Here, we report micromagnetic numerical simulation results about the grain boundary effect on the B-doped Sm(Fe<sub>0.8</sub>Co<sub>0.2</sub>)<sub>12</sub> thin film. We employed a periodic boundary condition (PBC)-applied thin film of thickness 100 nm and located Sm(Fe<sub>0.8</sub>Co<sub>0.2</sub>)<sub>12</sub> grains enveloped by the soft ferromagnetic grain boundary phase with relatively low saturation magnetization. Coercivity and remanence are calculated by hysteresis loops based on the steepest descent method [4]. We show that controlling the magnetic properties of the grain boundary phase or thickness of the grain boundary can influence coercivity and remanence. These boundary features adjust the exchange interaction among grain boundaries involved in domain wall pinning and domain nucleation. Our results could be used as a guideline to design the optimal grain boundary phase for high-performance permanent magnets.
Magnetic field tunability of a skyrmion diode
Dae-Han Jung,Hee-Sung Han,Ganghwi Kim,Suyeong Jeong,Ki-Suk Lee 한국자기학회 2021 한국자기학회 학술연구발표회 논문개요집 Vol.31 No.1
Magnetic skyrmions are topologically stable particle-like objects that are hailed as a potential technology for next-generation information storage and other processing applications. [1-5]. For device applications of magnetic skyrmions, it is essential to control the skyrmion motions by electrical means in geometrically confined boundaries. In this work, we show that a current-driven skyrmion motion can be unidirectionally controlled by forming an asymmetric shape of the device. Furthermore, we demonstrate tunability of the unidirectional motions in which the magnetic field can be used to switch on and off a circuit. A key working principle of the unidirectional motion and its tunability is investigated by micromagnetic numerical and analytical calculations. We believe that our results could provide guidelines to design skyrmion-based logic devices including a diode and a transistor element.