Physics Colloquium: Magnetic Nanoparticles: from Lab. To Fab.

Small is beautiful and powerful. This conclusion is evident if one considers the aim of developing smaller and hence more efficient devices. The most fascinating and promising aspects of materials and devices becoming smaller, however, are not associated with mere size reduction only but are related to fundamentally novel physical properties and effects appearing when decreasing the lengths scales of materials down to the nanometer scale. In recent years, great progress has been made in this respect and nano-sized materials with novel properties have already found or exhibit at least a great potential for applications in the fields of, e.g., optics, magnetism, electricity, catalysis, and biomedicine. Currently, unique physical properties of nanoparticles are under intensive research. One of the materials properties strongly affected by size reduction is the magnetic response. For example, the magnetization (per atom) and the magnetic anisotropy of Co nanoparticles can be greater than their related bulk specimens. The enhancement in the magnetization can be ascribed to the surface atoms which become the dominant phase as size decreases and for which the electronic structure can be varied because of the different symmetry compared to the bulk. In addition, the surface anisotropy is the responsible for the enhancement of the magnetic anisotropy of the magnetic nanoparticles, i.e. the lower symmetry of surface atomic sites leads to an enhanced anisotropy. 

Magnetic nanoparticles (Nanomagnets) can be classified to soft or hard magnetic materials. Soft magnetic materials such as Fe, Co, Ni or their alloys with Ru and Pt can be used for medical applications. One of the advantage of such particles that it can emit energy in a form of heat under applied external magnetic field and once the magnetic field is removed, no remnance magnetization will remain. This unique property can be used for cancer treatment which is called magnetic hyperthermia.  The other type of the magnetic nanoparticles is hard magnetic materials. CoxC, MnGa, and CoFeC nanoparticles are good examples of hard magnets which have the property of storing magnetic energy even after removing the magnetic field. Such property are commonly used for fabrication of permanent magnets. The main advantage of such particles is due to the higher magnetic anisotropy which can act as good candidate for new generation of magnetic data storage.  

When aiming at realizing the promises of applied nanomagnetism, however, many researches and challenges were required to be done in the last few years from the laboratory scale to fabrication scale. Therefore, the talk focusses on the synthesis of different types of magnetic nanoparticles and their potential for both medical and industrial applications.