Magnetic, electric and electron magnetic resonance properties of orthorhombic self-doped La_1-xMnO₃ single crystals

The effect of lanthanum deficiency on structural, magnetic, transport, and electron magnetic resonance (EMR) properties has been studied in a series of La_1-xMnO₃ (x = 0.01, 0.05, 0.11, 0.13) single crystals. The x-ray diffraction study results for the crystals were found to be compatible with a single phase of orthorhombic symmetry. The magnetization curves exhibit weak ferromagnetism for all samples below 138 K. It was found that both the spontaneous magnetization and the coercive field increase linearly with x. The pressure coefficient dT_N/dP decreases linearly with self-doping, from a value of 0.68 K kbar^-1 for La_0.99MnO₃ to 0.33 K kbar^-1 for La_0.87MnO₃. The resistivity of low-doped La_0.99MnO₃ crystal is of semiconducting character, while that of La_0.87MnO₃ depends weakly on temperature between 180 and 210 K. It was found that the magnetic and transport properties of the self-doped compounds may be attributed to a phase separation involving an antiferromagnetic matrix and ferromagnetic clusters. The latter phases as well as their paramagnetic precursors have been directly observed by means of EMR.