Unusually strong ferromagnetic correlations in La-doped CaMnO3

Magnetic susceptibility measurements are presented on specimens with the composition Ca1-xLaxMnO3 (0 less than or equal to x less than or equal to 0.10). Saturation moments at 5 K and 4000 Oe of under 0.6 mu(B)/Mn ion, where mu(B) is the Bohr magnetron, are observed; all specimens exhibit Curie-Weiss behavior above the Neel temperature T-N. CaMnO3 (i.e., x = 0) has a Curie-Weiss temperature Theta = 565 K. Substitution of La3+ for Ca2+ results in isolated Mn3+ ions which interact with the surrounding Mn4+ ions via double exchange. This interaction leads to a strong reduction of Theta, thereby indicating that a small number of Mn3+ ions is sufficient to produce strong ferromagnetic correlations above T-N. (C) 1999 American Institute of Physics. [S0021-8979(99)49808-1].