Tc and Jc distribution in in situ processed MgB2 bulk superconductors with/without C doping

Temperature dependence of magnetic moment (m−T) and the magnetization (M−H) at 5 K and 20 K of the in situ processed MgB2 bulk pellets with/without carbon (C) doping were examined. The superconducting critical temperature (Tc), the superconducting transition width (ΔT) and the critical current density (Jc) were estimated for ten test samples taken from the MgB2 bulk pellets. The reliable m−T characteristics associated with the uniform MgB2 formation were obtained for both MgB2 pellets. The Tcs and ΔTs of all test samples of the undoped MgB2 were the same each other as 37.5 K and 1.5 K, respectively. The Tcs and ΔTs of the C-doped MgB2 were 36.5 K and 2.5 K, respectively. Unlike the m−T characteristics, there existed the difference among the M−H curves of the test samples, which might be caused by the microstructure variation. In spite of the slight Tc decrease, the C doping was effective in enhancing the Jc at 5 K.