Calcium Deficiency and Its Influence on Structure, Magnetism, and Magnetocaloric Effects in La0.7Ca0.2-x□xSr0.1MnO3 (x = 0.00, 0.05, and 0.10) Manganites

Hole-doped lanthanum manganites with the formula La1-xAxMnO3 (A = Ca3+, Sr2+) exhibit rich magnetic and structural phenomena, including complex magnetic phase transitions and significant magnetocaloric effects (MCE). Recent studies on La0.7Ca0.2-x□xSr0.1MnO3 (x = 0.00, 0.05, 0.10) have shown that Ca2+ vacancies (□) induce changes in Mn oxidation states, structural disorder, and magnetic complexity near the Curie temperature (TC), contributing to anomalous MCE behavior. However, conventional magnetometry lacks the resolution to differentiate between coexisting or short-range magnetic phases. In this proposal, we seek to perform high-resolution neutron diffraction measurements using the GEM diffractometer to probe both nuclear and magnetic structures across a range of temperatures (100–350 K). This will enable detailed analysis of atomic positions, site occupancy, thermal displacements, and magnetic ordering, as well as nuclear density profiles via the maximum entropy method (MEM). By correlating these features with the enhanced -ΔSM, we aim to uncover the underlying structural and magnetic mechanisms responsible for the observed MCE. We request 3 days of beam time to complete a full temperature-dependent study of the three compositions under zero-field conditions.