Magnetic nanoparticles studied by synchroton radiation and rf transverse susceptibility

Figueroa García, Adriana Isabel

2013
Prensas Universitarias de Zaragoza Zaragoza
ISBN: 978-84-15770-49-7

Resumen: The fundamental understanding of nanoscale materials has been the focus of much scientific and technological interest over the last decades. Nanoparticles (NPs) are widely investigated not only as consequence of the general miniaturization of devices, but also because they constitute ideal systems to study finite-size and surface effects, those yielding new physical phenomena and enhanced properties with respect to their bulk counterpart. Magnetic NPs are especially interesting since the properties of the valence electrons of atoms (which are mainly responsible of the magnetic character of atoms and solids) change as they become part of a small particle and start to delocalize. Thus, their magnetic properties are very sensitive to size, composition, and local atomic environment, showing a wide variety of intriguing phenomena. This rich variety of behavior can be understood in general terms as arising from the reduced average coordination per atom, the quantum size effect and modified collective electron behavior such as screening and charge spill-out from the surface. The size of magnetic nanoparticles is comparable to the size of a magnetic domain, which results in a completely novel phenomenology with respect to bulk magnetic materials. Macroscopic magnetic materials reduce their energy by breaking into magnetic domains, or small regions where the spins are aligned. Each domain can have a magnetic moment which is oriented in a different direction from that of its neighbor. The creation of a domain increases the anisotropy energy of the system, defined as the change in the electronic energy, associated to the inversion of its magnetization; but it reduces the magnetostatic energy, so that the material is in average not magnetized (possessing a net magnetization) unless an external magnetic field is applied...

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DOI: 10.26754/uz.978-84-15770-49-7