Vacancies at Mn-site in Mn3+ rich manganites: a route to ferromagnetism but not to metallicity

The study of the Mn3+-rich manganites LaMn1−xO3 and La0.9Sr0.1Mn1−xO3 shows that the creation of Mn site vacancies induces or reinforces ferromagnetism and lowers the resistivity but does not induce an insulator to metal transition. This behavior is explained as a valence effect which induces the formation of Mn4+ species and consequently favors the double exchange, but is counterbalanced by the rupture of the Mn–O–Mn bonds due to the Mn vacancies which breaks the conduction paths and hinders a metallic conductivity.