Stoichiometry and electronic properties of LaMnO3

Treating off-stoichiometric (LaMn)(0.95)O-3 in hydrogen transforms its electrical and magnetic properties. The untreated material is a ferromagnetic narrow-gap semiconductor (T-c = 125 K) whereas the near-stoichiometric reduced material is an antiferromagnetic insulator T-N = 110 K) Although the off-stoichiometric manganite has formally the same mixed manganese valency as compounds such as (La0.7Ca0.3)MnO3 there is no resistivity peak at T-c and no giant magnetoresistance. The difference may be due to potential fluctuations associated with cation vacancies.