Electron Magnetic Resonance Study of Magnetic Order, Paramagnetic Magnetic Correlations, and Spin Dynamics in La- and Mn-Deficient LaMnO $_{3}$ Manganites

To probe magnetic ordering in single crystals of La_1-x MnO₃ (x = 0.01, 0.05, 0.13) and in ceramics of LaMn_1-yO₃ (y = 0, 0.02, 0.06), the X-band electron magnetic resonance measurements were carried out in the temperature range 5 K les T les 600 K. The temperature dependences of doubly integrated intensity of electron paramagnetic resonance signal and its linewidth were fitted with known theoretical models modified for taking into account the different mechanisms of spin relaxation. The experimental data and their fits evidence that Mn- and La-site vacancies dope the holes in parent LaMnO₃, which induces ferromagnetic double exchange interaction. However, strong structural and chemical disorder of La_1-xMnO₃ crystals makes the ferromagnetic ground state eventually impossible even at x = 0.13. In a contrast, better structural/chemical homogeneity together with a stronger impact of Mn-site vacancies on mixed manganese valence and double exchange are characteristic for LaMn_1-yO₃ ceramics. As a result, the LaMn_0.94O₃ compound appears to be ferromagnetic-like ordered and demonstrates band-like propagation of doped carriers.