Possible weak magnetism in MB6 (M:Ca, Ba) probed by muon spin relaxation and muon level-crossing resonance

The temperature dependence of muon spin relaxation rate exhibits a significant increase below ∼130 K in CaB6 and ∼110 K in BaB6, 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 CaB6. 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.