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Article

Unidirectional Magnetic Anisotropy in Molybdenum Dioxide–Hematite Mixed-Oxide Nanostructures

1
National Institute of Materials Physics, Atomistilor 405A, 077125 Magurele, Romania
2
Department of Physics, Duquesne University, Pittsburgh, PA 15282, USA
*
Author to whom correspondence should be addressed.
Academic Editor: Sam Lofland
Nanomaterials 2022, 12(6), 938; https://doi.org/10.3390/nano12060938
Received: 4 February 2022 / Revised: 7 March 2022 / Accepted: 8 March 2022 / Published: 12 March 2022
MoO2-Fe2O3 nanoparticle systems were successfully synthesized by mechanochemical activation of MoO2 and α-Fe2O3 equimolar mixtures throughout 0–12 h of ball-milling. The role of the long-range ferromagnetism of MoO2 on a fraction of more defect hematite nanoparticles supporting a defect antiferromagnetic phase down to the lowest temperatures was investigated in this work. The structure and the size evolution of the nanoparticles were investigated by X-ray diffraction, whereas the magnetic properties were investigated by SQUID magnetometry. The local electronic structure and the specific phase evolution in the analyzed system versus the milling time were investigated by temperature-dependent Mössbauer spectroscopy. The substantially shifted magnetic hysteresis loops were interpreted in terms of the unidirectional anisotropy induced by pinning the long-range ferromagnetic order of the local net magnetic moments in the defect antiferromagnetic phase, as mediated by the diluted magnetic oxide phase of MoO2, to those less defect hematite nanoparticles supporting Morin transition. The specific evolutions of the exchange bias and of the coercive field versus temperature in the samples were interpreted in the frame of the specific phase evolution pointed out by Mössbauer spectroscopy. Depending on the milling time, a different fraction of defect hematite nanoparticles is formed. Less nanoparticles supporting the Morin transition are formed for samples exposed to a longer milling time, with a direct influence on the induced unidirectional anisotropy and related effects. View Full-Text
Keywords: unidirectional anisotropy; exchange bias; coercive field; Morin transition; Mössbauer spectroscopy unidirectional anisotropy; exchange bias; coercive field; Morin transition; Mössbauer spectroscopy
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MDPI and ACS Style

Tolea, F.; Sorescu, M.; Diamandescu, L.; Iacob, N.; Tolea, M.; Kuncser, V. Unidirectional Magnetic Anisotropy in Molybdenum Dioxide–Hematite Mixed-Oxide Nanostructures. Nanomaterials 2022, 12, 938. https://doi.org/10.3390/nano12060938

AMA Style

Tolea F, Sorescu M, Diamandescu L, Iacob N, Tolea M, Kuncser V. Unidirectional Magnetic Anisotropy in Molybdenum Dioxide–Hematite Mixed-Oxide Nanostructures. Nanomaterials. 2022; 12(6):938. https://doi.org/10.3390/nano12060938

Chicago/Turabian Style

Tolea, Felicia, Monica Sorescu, Lucian Diamandescu, Nicusor Iacob, Mugurel Tolea, and Victor Kuncser. 2022. "Unidirectional Magnetic Anisotropy in Molybdenum Dioxide–Hematite Mixed-Oxide Nanostructures" Nanomaterials 12, no. 6: 938. https://doi.org/10.3390/nano12060938

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