MgB₂ 초전도 분말의 열처리 조건에 따른 초전도 특성 변화 연구

The variation of superconducting properties of pure MgB₂ superconducting powder samples after a heat treatment in an argon (Ar) atmosphere at temperatures of 550 ^◦C, 600 ^◦C, and 800 ^◦C for 0.5 h, 5 h, and 10 h were investigated. X-ray diffraction (XRD) analysis revealed that the sample heat-treated at 800 ^◦C for 10 h exhibited some impurity phases, such as MgB₄. According to magnetic moment versus temperature m(T) curve measurements under zero field cooling (ZFC) condition, it was confirmed that the superconducting critical transition temperature (T_c) of all prepared samples was the same at approximately 39 K. And magnetic moment versus magnetic field m(H) curves were obtained at temperatures of 10 K, 20 K, and 30 K, and then the critical current density (J_c) values were calculated by using the Bean critical state model. The pure MgB₂ powder sample without heat treatment exhibited the highest J_c value, while the sample heat-treated at 800 ^◦C for 10 h showed the lowest J_c value. The irreversibility field (H_irr) characteristics showed a deterioration in the sample heat-treated at 800 ^◦C for 10 h.