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Unprecedented Robust Antiferromagnetism in Fluorinated Hexagonal Perovskites

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journal contribution
posted on 20.07.2011 by Mihai Sturza, Houria Kabbour, Sylvie Daviero-Minaud, Dmitry Filimonov, Konstantin Pokholok, Nicolas Tiercelin, Florence Porcher, Laurent Aldon, Olivier Mentré
The diversification of antiferromagnetic (AFM) oxides with high Néel temperature is of fundamental as well as technical interest if one considers the need for robust AFM in the field of spin-tronics (exchange bias, multiferroics, etc.). Within the broad series of so-called hexagonal perovskites (HP), the existence of face-sharing octahedral units drastically lowers the strength of magnetic exchanges as compared to corner-sharing octahedral edifices. Here, we show that the partial introduction of F in several Fe-based HP types leads to a drastic increase of the AFM ordering close to the highest values reported in iron oxides (TN ≈ 700 K). Our experimental results are supported by ab initio calculations. The TN increase is explained by the structural effect of the aliovalent F for O2– substitution occurring in preferred anionic positions: it leads to local changes of the Fe–O–Fe connectivity and to chemical reduction into predominant Fe3+, both responsible for drastic magnetic changes.