Structural, morphological, and magnetic characterizations of (Fe0.25Mn0.75)2O3 nanocrystals: A comprehensive stoichiometric determination

Abstract

This report aims to investigate in depth FeMnO3, a material of interest due to its fascinating magnetic and multiferroic properties and its many applications in fields including lithium-ion batteries, microwave devices, and catalysis. However, understanding the precise stoichiometry of the material is crucial for a better comprehension of its physical properties. A cheap, simple, and repeatable sol-gel process was used to fabricate the FeMnO3 nanocrystals. Comprehensive multi-technique characterization of the as-fabricated FeMnO3 indicates that the main phase (94 wt%) is Fe0.5Mn1.5O3, although hematite appears as the minority phase (6 wt%). Magnetic characterization shows core-shell spin-glass like behavior, as well as paramagnetic-ferrimagnetic transitions and a Griffiths phase regime. EPR measurements revealed a strong and broad resonance line across the temperature range of 4.3 K–300 K, primarily influenced by the majority phase. The g-value decreases monotonically from 2.93 at 50 K to 2.18 at 300 K. There is a notable change in the resonance field and linewidth between 40 and 50 K, attributed to surface spin glass behavior. The EPR data below 50 K are in line with the core-shell model of (Fe0.25Mn0.75)2O3 nanoparticles. Below 50 K, the shell's spin system undergoes a transition from paramagnetic to spin-glass-like, with a critical temperature around 43 K. Above 50 K, the superparamagnetic minority phase significantly affects the temperature dependence of the resonance linewidth. These results hold particular importance as they advance our understanding of the intricate magnetic interactions present in FeMnO3. For the best possible use of this material platform in new technologies, such insights are essential.