Impact of Alkali Ions Codoping on Magnetic Properties of La0.9A0.1Mn0.9Co0.1O3 (A: Li, K, Na) Powders and Ceramics

Abstract

The aim of the work was to check how the introduction of alkali and cobalt ions into a manganese structure can affect the structural disorder and, in consequence, lead to the changes (improvements) of magnetic properties. The high-pressure sintering technique was applied to check if the external factor can modify the magnetization of manganites. Nanocrystalline La0.9A0.1Mn0.9Co0.1O3 (where A is Li, K, Na) powders were synthesized by the combustion technique. The respective powders were used for nanoceramics preparation by the high-pressure sintering technique. The structure and morphology of the compounds were studied by X-ray powder diffraction, scanning electron microscopy and energy-dispersive X-ray spectroscopy. Magnetization studies for all compounds were performed in order to check the changes induced by either codoping or the sintering pressure. It was found that the type of the dopant ion and sintering pressure produced significant changes to the magnetic properties of the studied compounds. Alkali ions lead to the stabilization of Co ions in the +2 oxidation state and the formation of positive exchange interactions Mn3+–Mn4+ and Co2+–Mn4+ and the subsequent increase in remanent magnetization. High sintering pressure leads to a decrease in grain size and reduction of long-range ferromagnetic order and lower magnetization.

Controlling the Magnetic Properties of La0.9A0.1Mn0.9Cr0.1O3 (A: Li, K, Na) Powders and Ceramics by Alkali Ions Doping

“…Magnetochemistry 2023, 9, x. https://doi.org/10.3390/xxxxx www.mdpi.com/journal/magnetochemistry described in the mentioned model assuming that about 20% of the manganese ions are in 4+ oxidation state, which is in accordance with our previous study [33]. Chemical substitution with alkali elements and chromium ions leads to only slight changes in the structural parameters thus assuming a stabilization of dominant 3+ oxidation state of the chromium ions having ionic radius (0.615Å) similar to that specific for Mn 3+ ions (0.645Å) [56].…”

“…The mixed magnetic state of the initial compounds is associated with a deficient cation content formed during the synthesis procedure thus leading to the formation of competing positive and negative exchange interactions between isovalent and heterovalent manganese ions [55]. The magnetization value obtained for LaMnO 3 compound can be described in the mentioned model assuming that about 20% of the manganese ions are in 4+ oxidation state, which is in accordance with our previous study [33].…”

“…In this work, we continue our systematic work, where the manganites were doped with alkali ions [32] and then doped with cobalt ions [33]. The results obtained in our previous works have shown that chemical doping with alkali metal ions and Co ions, along with the different synthesis methods, can be considered an effective tool for the controllable modification of the electronic configuration of the Mn and Co ions, and thus, the functional properties of the doped manganites.…”