Resonance and magnetic study of polycrystalline La0.9 Ca0.1 Mn O3: Evidence of nonstoichiometry induced inhomogeneous magnetic ground state

Electron magnetic resonance and ac and dc magnetic measurements in respective temperature intervals 75-600 and 5-300 K were employed to probe and to compare magnetic ordering in two manganite ceramics with close composition: La0.9 Ca0.1 Mn O3 and (La0.9 Ca0.1) 0.99 Mn O3. X-ray powder diffraction and dc low field magnetic measurements proved that lattice parameters and Curie temperatures of both compounds are close to each other. However, ac susceptibility, high field dc magnetic measurements, and resonance experiments have shown that the (La0.9 Ca0.1) 0.99 Mn O3 sample is characterized by stronger ferromagnetic correlations, higher spontaneous magnetization at low temperatures, and weaker effective magnetic anisotropy than the La0.9 Ca0.1 Mn O3 one. The results obtained are discussed in the frame of experimentally proven inherent nonstoichiometry model, which takes into account cation vacancies in La and Ca sites appearing in low-doped La-Ca-Mn-O samples sintered in an air atmosphere. The studied samples are supposedly characterized by random distribution of cation vacancies and represent an intermediate case between fully stoichiometric and nonstoichiometric ones. This may explain strong and unpredictable influence of weak compositional change on the magnetic ordering. The nonstoichiometry seems to be generally responsible for previously reported difference in magnetic ordering between low-doped La-Ca-Mn-O ceramics and single crystals of the same nominal composition.