Observations were made of the conduction electron spin resonance in fine powders in both the superconducting and normal states. The Pauli susceptibility was equal to 2.0 x 10-5emu/mol at 450 to 600K. The spin relaxation rate exhibited an anomalous temperature dependence. The conduction electron spin resonance measured below TC at several frequencies suggested that MgB2 was a strongly anisotropic superconductor with an upper critical field, HC2, ranging from 2 to 16T. The high-field reversible magnetization data of a randomly oriented powder sample were well described by assuming that MgB2 was an anisotropic superconductor with HC2-ab/HC2-C ratios of 6 to 9.

Anisotropy of Superconducting MgB2 as Seen in Electron Spin Resonance and Magnetization Data. F.Simon, A.Janossy, T.Feher, F.Muranyi, S.Garaj, L.Forro, C.Petrovic, S.L.Budko, G.Lapertot, V.G.Kogan, P.C.Canfield: Physical Review Letters, 2001, 87[4], 047002 (3pp)