Electronic phase-separation in Mg1-xB2 probed by CESR

Temperature dependent conduction electron spin resonance (CESR) was performed in the normal and vortex-state of Mg1-xB2. Fine powder of polycrystalline samples with x congruent to 0 and 0.15 were studied at 9.48 GHz (H-y similar or equal to 3380 Oe). Our results suggest the interesting effect associated with the presence of Mg deficiency in this compound: a phase separated Mg-vacancy rich (insulating) and Mg-vacancy poor (superconducting metal) regions for the x similar or equal to 0.15 sample. The depinning temperature, T-p for x similar or equal to 0.15 sample was obtained and confronted with previous results. (C) 2004 Elsevier B.V. All rights reserved.