The magnetic relaxation of MgB2 powder

Magnetic relaxation properties of pure MgB2 powder samples and diluted water-treated MgB2 powder samples were investigated. The magnetic field H-dependence, m(H), and the time t-dependence, m(t), of the magnetic moment m were measured and analyzed using the PPMS-VSM magnetometer equipment, respectively. The m(t) reduction rates of pure MgB2 powder samples and diluted water-treated MgB2 powder samples decreased to about 0.7 --1.8% and 0.6 --1.0% for about 7200 s, respectively, at temperature T = 15 K. The magnetic relaxation properties of the two types of MgB2 powders were analyzed by calculating the magnetic relaxation rate S = -dln(Mirr)/dln(t) values according to Anderson-Kim theory. The magnetic relaxation ratio S values of the two types of MgB2 powder samples were almost similar. As a result of the quantum creep effect, the constant magnetic relaxation rate S characteristic was confirmed at a temperature range of T = 10 K or less.