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

Abstract

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 PrMn 0.9 O 3 (ABO 3 ) 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 PrMn 0.9 O 3 NPs. The concurrent decrease of lattice cell volume and Mn−O−Mn bond angles near the AFM to FM transition temperature (T c ) suggests that the AFM character increases just above T c 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 Pr 0.9 MnO 3.2 NPs.

Maneuvering the Physical Properties and Spin States To Enhance the Activity of La–Sr–Co–Fe–O Perovskite Oxide Nanoparticles in Electrochemical Water Oxidation

“…The three-dimensional views of crystal structures were obtained using VESTA 3 software. Oxygen nonstoichiometry was calculated using thermogravimetric method . FESEM images were recorded with Carl Zeiss SUPRA 55VP FESEM instrument.…”

“…Oxygen nonstoichiometry was calculated using thermogravimetric method. 51 FESEM images were recorded with Carl Zeiss SUPRA 55VP FESEM instrument. The ICP-MS measurements were carried out in a PerkinElmer Optima 2100 DV instrument.…”

Coexistence of High Magnetization and Anisotropy with Non-monotonic Particle Size Effect in Ferromagnetic PrMnO3 Nanoparticles

“…The magnetizations at 50 kOe are 55, 84, and 51 emu/g for P1, P2, and P3, respectively. It is noteworthy to mention here that the magnetization of P2 is the highest for any Pr–Mn–O system at least with a similar particle size. ,,,,,− Furthermore, the non-monotonic change in magnetization with particle size is untraditional in manganite systems. Whereas in La-based pristine or doped manganites it is well-known that magnetization increases with increase in particle size, ,, Pr-based systems behave differently.…”

“…Manganite nanoparticles (NPs) are the subject of intense research owing to their unique magnetic properties which differ significantly from their bulk counterparts. − The lesser studied antiferromagnetic (AFM) PrMnO 3 may be converted to its ferromagnetic (FM) phase at reduced dimensions especially due to oxygen excess in the lattice. , Upon exposure to air, oxygen diffuses through the NP surface incorporating additional oxide ions, which in turn oxidize a few Mn 3+ ions into Mn 4+ to create the Mn 3+ –O–Mn 4+ units. The FM character is a result of double exchange between different valence states of Mn through the intermediate O 2– .…”

“…The interconnected NPs with high crystallinity and large grain boundary fractions can be stabilized by a nonaqueous sol–gel synthesis method. This method among several other synthesis methodologies has been shown to be beneficial for obtaining temperature-dependent magnetic phase transitions, high FM moments, and large magnetoresistance. , The nonaqueous solvent limits the NP size by C–O bond breaking and making of new M–O bonds . The absence of water molecules prevents hydrolysis, which further retards particle agglomeration in solution.…”