Exploring the magnetic disorder in Ultrahin Iron Oxide Hollow Nanoparticules

Magnetic nanoparticles are of special interest in the field of storage information and nanomedicine (hyperthermia, medical imagery, …). Due to the nanometric size of the particles they can be guided using a magnetic field. Unfortunately, reducing the size of the nanomagnets leads to magnetic instability incompatible to technological applications. Modifying the shape of the nanoparticles (core-shell particles, Hollow particles, …) lead to an exaltation of surface/interface effects and an enhancement of the magnetic anisotropy and the apparition of dynamical effect (superparamagnetic). As an example, by use of in-field Mössbauer spectrometry, we have shown the existence of complex non-collinear magnetic structure in iron oxide hollow nanoparticles. Indeed, this structure consists in a ferrimagnetic layer of few atomic planes confined between two layers with canted structure resulting from two antiferromagnetic coupled speromagnetic structures. Such a magnetic structure leads to an increase of the magnetic coupling between the interfacial moments of the magnetic phases. The exchange bias coupling finally tends to increase the magnetic anisotropy of the nanoparticles and in definitive the magnetic stability of the nanostructure.

Properties of Hollow magnetic nanoparticle.

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