Magnetic nanoparticles: from the nanostructure to the physical properties

Abstract

Some of the synthesis methods and physical properties of iron-oxide based magnetic nanoparticles such as Fe3-xO4 and CoxFe3-xO4 are reviewed because of their interest in health, environmental applications, and ultra-high-density magnetic recording. Unlike high crystalline quality nanoparticles larger than a few nanometers that show bulk-like magnetic and electronic properties, nanostructures with increasing structural defects yield a progressive worsening of their general performance due to frozen magnetic disorder and local breaking of their crystalline symmetry. Thus, it is shown that single-crystal, monophasic nanoparticles do not exhibit significant surface or finite-size effects, such as spin canting, reduced saturation magnetization, high closure magnetic fields, hysteresis-loop shift or dead magnetic layer features which are mostly associated with crystallographic defective systems. Besides, the key role of the nanoparticle coating, surface anisotropy, and inter-particle interactions are discussed. Finally, the results of some single particle techniques -- magnetic force microscopy, X-ray photoemission electron microscopy, and electron magnetic chiral dichroism -- that allow studying individual nanoparticles down to sub-nanometer resolution with element, valence and magnetic selectivity, are presented. All in all, the intimate, fundamental correlation of the nanostructure (crystalline, chemical, magnetic) to the physical properties of the nanoparticles is ascertained.

References in corpus (22)

• Learning from Nature to Improve the Heat Generation of Iron-Oxide Nanoparticles for Magnetic Hyperthermia Applications
• Switching of magnetization by non-linear resonance studied in single nanoparticles
• Bit Patterned Magnetic Recording: Theory, Media Fabrication, and Recording Performance
• Surfactant effects in monodisperse magnetite nanoparticles of controlled size
• Enhancement of the magnetic anisotropy of nanometer-sized Co clusters: influence of the surface and of the inter-particle interactions
• Effective anisotropies and energy barriers of magnetic nanoparticles with Neel surface anisotropy
• Microscopic origin of exchange bias in core/shell nanoparticles
• Magnetic nanoparticles with bulk-like properties
• Embracing defects and disorder in magnetic nanoparticles
• Vanishing Fe 3d orbital moments in single-crystalline magnetite
• Surface anisotropy broadening of the energy barrier distribution in magnetic nanoparticles
• Surface-induced cubic anisotropy in nanomagnets
• Magnetic relaxation in terms of microscopic energy barriers in a model of dipolar interacting nanoparticles
• Field Dependence of Magnetic Disorder in Nanoparticles
• Controlling exchange bias in Co-CoOx nanoparticles by oxygen content
• Modelling exchange bias in core/shell nanoparticles
• Particle size and cooling field dependence of exchange bias in core/shell magnetic nanoparticles
• Quantification of dipolar interactions in Fe${}_{3-x}$O${}_4$ nanoparticles
• Interplay between surface anisotropy and dipolar interactions in an assembly of nanomagnets
• Resolving complex spin textures in nanoparticles by magnetic neutron scattering
• Exchange bias and asymmetric hysteresis loops from a microscopic model of core/shell nanoparticles
• Magnetic Domains and Surface Effects in Hollow Maghemite Nanoparticles

Cited by in corpus (6)

• Perspective: magnetic nanoparticles in theranostic applications
• Magnetic neutron scattering from spherical nanoparticles with Neel surface anisotropy: Atomistic simulations
• Magnetic neutron scattering from spherical nanoparticles with Neel surface anisotropy: Analytical treatment
• A feasibility analysis towards the simulation of hysteresis with spin-lattice dynamics
• Role of nanoparticle shape on the critical size for quasi-uniform ordering: from spheres to cubes through superballs
• Role of positional disorder in fully textured ensembles of Ising-like dipoles