Extensive Parallelism between Crystal Parameters and Magnetic Phase Transitions of Unusually Ferromagnetic Praseodymium Manganite Nanoparticles

The alterations in physical property across different space groups of the same material are sometimes conveniently reflected by the crystal structure as a function of temperature. However, mirroring the physical property and crystal parameters over a wide range of temperatures within the same space group is quite unusual. Remarkably, Rietveld analyses of the X-ray diffraction patterns of PrMn0.9O3 (ABO3) nanoparticles (NPs) with a constant Pnma space group from 300 to 10 K could successfully predict the four magnetic phases, viz. paramagnetic, antiferromagnetic (AFM), ferromagnetic (FM), and spin-glass-like ordering. The increase in Mn–O–Mn bond angles and tolerance factor leads to FM ordering below ∼100 K in usually AFM PrMn0.9O3 NPs. The concurrent decrease of lattice cell volume and Mn–O–Mn bond angles near the AFM to FM transition temperature (Tc) suggests that the AFM character increases just above Tc due to atomic deformations and reduced Mn–Mn separation. The predictions from crystal structure refinement were successfully verified from the cooling path of the temperature-dependent field-cooled magnetization measurements. A mechanism involving incoherent spin reversal due to competition between the neighboring spins undergoing antiparallel to parallel spin rotations was suggested. The structure–property parallelism was cross-checked with the A-site vacant Pr0.9MnO3.2 NPs.