Ferromagnetic and antiferromagnetic interactions in lanthanum cobalt oxideat low temperatures - art. no. 174401

Systematic dc and ac magnetic susceptibility studies have been performed on single-phase LaCoO3 powder samples. Evidence is presented in support of th e existence of ferromagnetic (FM1, FM2) and antiferromagnetic (AFM) interac tions at low temperatures. FM1 and FM2 are ferromagnetic interactions that occur at different temperature regimes and their proposed origin is differe nt. Specifically, FM1 interactions are observed at very low temperatures (T < 10 K) and are attributed to superexchange interactions of the type Co-IV -O-Co-s (where s = iii or 3+). FM2 interactions are observed for 20<T<100 K and are attributed to coupling of localized moments on Co-IV sites through RKKY interactions. The weak AFM interactions set in at T<similar to>28 K a re attributed to the strong electron correlations in the system. The existe nce of the weak AFM may constitute evidence in support of the proposal that this system is a Mott-Hubbard insulator. The fact that the onset temperatu re of AFM is different from that of the metal-to-insulator transition is at tributed to the presence of magnetic impurities (Co-IV). The existence of C o-IV is based on the results of iodometric titrations. and attributed to La vacancies. A consistent qualitative explanation is provided for available magnetic and transport data.