Anisotropy of superconducting MgB2 as seen in electron spin resonance and magnetization data -: art. no. 047002

We observed the conduction electron spin resonance (CESR) in fine powders of MgB2 both in the superconducting and normal states. The Pauli susceptibility is chi (s) = 2.0 x 10(-5) emu/mole in the temperature range of 450 to 600 K. The spin relaxation rate has an anomalous temperature dependence. The CESR measured below T-c, at several frequencies suggests that MgB2 is a strongly anisotropic superconductor with the upper critical field, H-c2, ranging between 2 and 16 T. The high-field reversible magnetization data of a randomly oriented powder sample are well described assuming that MgB2 is an anisotropic superconductor with H-c2(ab)/H-c2(c) approximate to 6-9.