AUTHOR=Sakuda Masahiro , Yamahara Hiroyasu , Tabata Hitoshi , Seki Munetoshi 

TITLE=Control of Magnetic Properties of Barium Ferrite Thin Films With Unusual Valence Fe

JOURNAL=Frontiers in Materials

VOLUME=8

YEAR=2021

URL=https://www.frontiersin.org/journals/materials/articles/10.3389/fmats.2021.732676

DOI=10.3389/fmats.2021.732676

ISSN=2296-8016

ABSTRACT=<p>Thin films of BaFe<sub>1-<italic>x</italic></sub>M<sub><italic>x</italic></sub>O<sub>3</sub> (M = Hf, Zr, and Ce; 0.0 ≤ <italic>x</italic> ≤ 0.75) were fabricated using pulsed laser deposition and their magnetic properties were investigated. X-ray diffraction analysis indicated that oxygen-deficient BaFeO<sub><italic>x</italic></sub> (<italic>x</italic> &lt; 3.0) with a monoclinic structure was formed when the deposition was conducted using a non-substituted target (<italic>x</italic> = 0.0). The as-grown BaFeO<sub><italic>x</italic></sub> films were converted into fully oxidized BaFeO<sub>3</sub> with a perovskite structure by low-temperature oxidation in an ozone atmosphere. In contrast, the as-deposited films of Hf, Zr, and Ce-substituted films exhibited a perovskite structure, and their crystallinity did not change after low-temperature ozone annealing. The magnetic transition temperature <italic>T</italic><sub>c</sub> of the BaFeO<sub>3</sub> film was 115 K, whereas the substituted BaFeO<sub>3</sub> films showed ferromagnetic behavior even at 300 K. These results can be attributed to the weakening of the antiferromagnetic super-exchange coupling among Fe ions owing to the lattice expansion in the substituted BaFeO<sub>3</sub>. In addition, the magnetization of the films was found to increase with the decreasing ionic ratio of Fe<sup>4+</sup>/Fe<sup>3+</sup>, suggesting that the inherent carrier-induced ferromagnetic interaction is dominant in the films.</p>