Goswami, Sudipta and Sahoo, Aditi and Bhattacharya, Dipten and Karci, Ozgur and Mohanty, P K (2020) Large structure-dependent room temperature exchange bias in self-assembled BiFeO3 nanoparticles. APL Materials, 8 (8). Art No-081101. ISSN 2166-532X

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We studied the magnetic properties of self-assembled aggregates of BiFeO3 nanoparticles (similar to 20 nm-40 nm). The aggregates formed two different structures-one with limited and another with massive crosslinking-via the ``drying-mediated self-assembly'' process following dispersion of the nanoparticles within different organic solvents. They exhibit large coercivity H-C (>1000 Oe) and exchange bias field H-E (similar to 350-900 Oe) in comparison to what is observed in isolated nanoparticles (H-C similar to 250 Oe; H-E similar to 0). H-E turns out to be switching from negative to positive depending on the structure of the aggregates, with |+H-E| being larger. Magnetic force microscopy reveals the magnetic domains (extending across 7-10 nanoparticles) as well as the domain switching characteristics and corroborates the results of magnetic measurements. Numerical simulation of the ``drying-mediated self-assembly'' process shows that the nanoparticle-solvent interaction plays an important role in forming the ``nanoparticle aggregate structures'' observed experimentally. Numerical simulation of the magnetic hysteresis loops, on the other hand, points out the importance of spin pinning at the surface of nanoparticles as a result of surface functionalization of the particles in different suspension media. Depending on the concentration of pinned spins at the surface pointing preferably along the easy-axis direction-from greater than 50% to less than 50%-H-E switches from negative to positive. Quite aside from the bulk sample and isolated nanoparticle, nanoparticle aggregates-resulting from surface functionalization-therefore offer remarkable tunability of properties depending on structures.

Item Type: Article
Subjects: Engineering Materials
Depositing User: Bidhan Chaudhuri
Date Deposited: 04 Feb 2021 07:55
Last Modified: 09 Feb 2021 05:36
URI: http://cgcri.csircentral.net/id/eprint/4891

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