Study of (La_1-xCa_x)MnO₃. II. Magnetic Properties

Abstract

Samples of polycrystalline (La 1- x Ca x )MnO 3 , where x takes the values ranging from 0.005 to 0.3, were studied experimentally. Stoichiometric specimens were made by carefully controlling the oxygen partial pressure. For specimens with x less than 0.1, the Néel temperature T N is almost constant at 141°K, while the paramagnetic Curie temperature \(\varTheta_{\text{P}}\) increases with x . For specimens with x greater than 0.1, both T N (or T C ) and \(\varTheta_{\text{P}}\) both increase almost linearly with x . The usual Mn 55 NMR spectra associated with Mn 3+ and Mn 4+ ions are observed for x ≤0.175. Motionally narrowed spectra are observed for x =0.2 and x =0.3. These results can be qualitatively explained by assuming that the d -holes at the sites around Ca 2+ ions contribute both to the electrical conduction and to the ferromagnetic interaction.