Impact of Mg substitution in LaMnO₃ manganites on their structural integrity and magnetic behavior

In this study, we investigated the impact of Mg substitution at the La site in LaMnO₃ on its structural, chemical, and magnetic properties. To explore the effects of Mg doping, we synthesized a series of compositions, La_1- Mg MnO₃ (x = 0.05, 0.1, 0.15, 0.2, 0.3, and 0.33), using a conventional solid-state method and systematically investigated their structural and magnetic properties. X-Ray diffraction patterns confirmed the formation of a pure rhombohedral crystal structure for the samples up to x = 0.15. However, for compositions with x > 0.15, the emergence of a secondary phase, MgMn₂O₄ with a spinel structure, was observed alongside the primary phase. Furthermore, it was observed that the secondary phase systematically increases with increasing Mg concentration. The temperature variations in magnetic studies, measured under zero-field-cooled (ZFC) and field-cooled (FC) conditions, confirmed that the transition temperatures for all the samples were found to be below 200 K, and these temperatures were observed to decrease with increasing Mg content. Negative magnetization was observed in the low-temperature ZFC curves for the samples with x > 0.2, indicating a difference in temperature-dependent magnetization due to the presence of two different structural phases. This effect became more prominent with the increase in the secondary phase, MgMn₂O₄. The magnetic studies revealed the co-existence of ferromagnetic and ferrimagnetic ordering in La_1- Mg MnO₃ for x > 0.15 samples, while ferromagnetic ordering was retained for the samples with x < 0.15, which was further corroborated by the isothermal hysteresis results.