Magnetic and electronic phase diagram of a ferromagnetic La_(0.6)Pb_(0.4)Mn_(1-x)Ru_xO_3 series

摘要

The nature of the magnetic interactions between Mn and Ru in La_(0.6)Pb_(0.4)Mn_(1-x)Ru_xO_3 where 0 ≤ x ≤ 1 have been explored by magnetic and transport measurements. The ferromagnetic Curie temperature decreases from 345 K to 105 K for x = 0.0 up to x = 0.9, while the metal-insulator transition is accompanied by the Curie temperature up to x = 0.4. These results indicate that double exchange ferromagnetic interaction is predominating over the superexchange ferromagnetic and superexchange anti-ferromagnetic interactions up to x = 0.4, in contrast to the other 3d dopant elements such as Ti, Cr, Fe, Co, Ni and Cu. We attribute the long-range ferromagnetic interaction and a dominant DE process to the variable valence states of Ru (Ru~(4+)/Ru~(5+)) as inferred from the X-ray absorption spectroscopic studies (XAS). The similar e_g parentage of Ru~(5+) (t_2g~3 e_g~0) to Mn~(4+) (t_2g~3 e_g~0) provides a template for the Mn~(3+) (t_(2g)~3 e_g~1) center to prolong the double exchange interaction using e_g electron itinerancy.