Preparation and Magnetic Properties of Cobalt-Doped FeMn2O4 Spinel Nanoparticles

Facile Synthesis of Chromium-Doped Fe1.1Mn1.9O4 Nanoparticles and the Effect of Cr Content on Their Magnetic and Structural Properties

In the present study, Fe1.1(CrxMn1-x)1.9O4 nanoparticles (0 ≤ x ≤ 0.5) were successfully synthesized by a combustion method, and the influence of Cr substitution on the structural and magnetic properties of the obtained nanoparticles was studied by various methods. The structural analysis revealed that the sample with x = 0 has a tetragonal structure, while all Cr-doped samples crystallize into a cubic structure. Additionally, the results of TEM show that doping with chromium leads to an increase in particle size. The magnetic hysteresis loops demonstrate the behavior typical for soft magnetic materials with low coercivity and remanence magnetization. The magnetic measurements revealed that the saturation magnetization of the obtained nanoparticles demonstrates a decreasing trend with increasing Cr content. The influence of chromium doping on the observation change in saturation magnetization is discussed. Based on the results of temperature-dependent magnetization measurements, it was found that the temperature of a magnetic transition in synthesized nanoparticles depends on Cr content.

Magnetic properties, magnetocaloric effect, and critical behaviors in Co1-x Cr x Fe2O4

This research work focuses on the magnetic properties, nature of the magnetic phase transition, magnetocaloric effect, and critical scaling of magnetization of various Co_1−xCr_xFe₂O₄ (x = 0, 0.125, 0.25, 0.375, and 0.5). The tunability of the magnetic moment, exchange interactions, magnetocrystalline anisotropy constant, and microwave frequency using Cr³⁺ content has been found. The nature of the magnetic phase transitions for all the Cr³⁺ concentrations exhibits as second order which has been confirmed from the analysis of critical scaling, universal curve scaling, and scaling analysis of the magnetocaloric effect. The critical exponent analysis for all samples was performed from the modified Arrott-, and Kouvel–Fisher-plots. These critical analyses suggest that x = 0.125, 0.250, and 0.375 samples show reliable results in the magnetocaloric effect with relative cooling power (RCP) values in the range of 128–145 J kg⁻¹. On the other hand, x = 0.00, and 0.500 samples exhibit inconsistent RCP values. The universal curve scaling also confirms the reliability of the magnetocaloric effect of the investigated samples.

Magnetic entropy change as a function of temperature for various Co_1−xCr_xFe₂O₄ at an applied magnetic field of 5 T.

Fe3+ in a tetrahedral position determined the electrocatalytic properties in FeMn2O4

As an electrocatalyst for the oxygen evolution reaction (OER) for water decomposition purposes, spinel ferrite materials have gained a lot of attention from many researchers. Herein, we document a co-precipitation synthesis of antitypical spinel nanoparticles (FeMn₂O₄) by post-annealing at different temperatures to enable modulation of the cationic oxidation state and tuning of the conversion degree for efficient and good OER performance. The electrocatalytic activity test shows that the sample annealed at 500 °C has the most optimal catalytic activity with an overpotential of 360 mV at a current density of 10 mA cm⁻² and a Tafel slope as low as 105.32 mV dec⁻¹. The formation of FeOOH during in situ OER promotes the catalytic activity of the catalysts. More importantly, according to the results of Brunauer–Emmett–Teller normalization, we demonstrate that the activity of the catalyst is also inseparable from the internal crystal structure. This work broadens the field of research on the electrocatalysis of spinel manganese ferrites.

Inspired by the flexibility of cation exchange and valence state variation in spinel ferrite, a high activity OER catalyst FeMn₂O₄ has been observed without inducing the change of composition, morphology, and atomic doping.