Comment on 'La0.95Mg0.05MnO3: an ideal

In a recent paper (Zhao J H, Song T, Kunkel H P, Zhou X Z, Roshko R M and Williams G 2000 J. Phys.: Condens. Matter 12 6903), Zhao et al reported detailed measurements on the magnetic properties of LaMnO3 with 5 at.% of the divalent cation Mg substituted in, which shows semiconducting ferromagnetic behaviour at low temperatures. This system has been shown to be an ideal ferromagnet with isotropic, three-dimensional Heisenberg behaviour and to have some unusual characteristics at low temperatures, in contrast with LaMnO3 with comparable levels of Ca doping. It is shown here that the authors have actually studied the magnetic properties of the self-doped compound La0.95MnO3 for which the reported properties are not unusual. The interesting electrical and magnetic properties of the substituted perovskite manganates La1−xAxMnO3 (A = Ca, Sr and Ba), where the trivalent La ions in LaMnO3 are replaced partly by divalent alkali metal ions, were first reported by Jonker and Van Santen in 1950 [1]. These interesting electrical and magnetic properties were found to be due to the conversion of a proportion of the Mn 3+ in LaMnO3 to Mn 4+ for charge compensation. Later studies have shown