Possible weak magnetism in MB_6 (M:Ca, Ba) probed by muon spin relaxation and muon level-crossing resonance

摘要

The temperature dependence of muon spin relaxation rate exhibits a significant increase below ～130 K in CaB_6 and ～110 K in BaB_6, while no sigh of spontaneous muon precession signal under a zero field is observed. Moreover, the electric field gradient at the boron site measured by muon level-crossing resonance (μLCR) exhibits a step like change at ～110 K in CaB_6. These results suggest a change in electronic state and the associated emergence of weak random magnetism below 110-130 K in these alkaline earth hexaborides.