Evolution of the Eu2+ local environment in Ca1−Eu B6

Abstract The local environment of Eu 2+ (4 f 7 ,S= 7 2 ) in Ca 1−x Eu x B 6 (0.003⩽x⩽0.10 and x=1.00) was studied by electron spin resonance. For x=0.003 the spectra show resolved fine and hyperfine structure due to the electric cubic crystal field and nuclear hyperfine field, respectively. The observed Lorentzian line shape indicates an insulating environment for the Eu2+ ions. As x increases (x>0.003) the lines broaden and became Dysonian in shape, suggesting a metallic environment for the Eu2+ ions. In contrast to our previous work in Ca1−xGdxB6, the resolved fine structure can be observed in the metallic regime up to x≃0.10 and no coexistence of insulating/metallic-like spectra was found.