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

• Published in: Nanomaterials (Basel, Switzerland) Vol. 12; no. 6; p. 938
• Main Authors: Tolea, Felicia, Sorescu, Monica, Diamandescu, Lucian, Iacob, Nicusor, Tolea, Mugurel, Kuncser, Victor
• Format: Journal Article
• Language: English
• Published: Switzerland MDPI AG 12.03.2022; MDPI
• Subjects: Anisotropy; Antiferromagnetism; Ball milling; coercive field; Coercivity; Electronic structure; Evolution; exchange bias; Ferric oxide; Ferromagnetism; Hematite; Hysteresis loops; Magnetic anisotropy; Magnetic measurement; Magnetic moments; Magnetic properties; Molybdenum; Molybdenum oxides; Morin transition; Mossbauer spectroscopy; Mössbauer spectroscopy; Nanoparticles; Particle size; Spectroscopy; Spectrum analysis; Superconducting quantum interference devices; Temperature dependence; unidirectional anisotropy; X-ray diffraction; Morin transition; coercive field; unidirectional anisotropy; Mössbauer spectroscopy; exchange bias
• ISSN: 2079-4991; 2079-4991
• DOI: 10.3390/nano12060938

MoO -Fe O nanoparticle systems were successfully synthesized by mechanochemical activation of MoO and α-Fe O equimolar mixtures throughout 0-12 h of ball-milling. The role of the long-range ferromagnetism of MoO 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 MoO , 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.