Objectives and Scope
Nanoscale magnets, which we define as magnetic entities with a size ranging between 2 and 100 nm, have a large application potential in the areas of magnetic storage and sensor technology as well as in the area of biomedical applications. For these small structures the role of the surface becomes important and governs the magnetic properties to a large extent. Dramatic changes of the magnetic anisotropy, the magnetic moment and the magnetic ordering temperature are expected. In addition these nanoscale structures can be used as the building blocks for new complex macroscopic materials. Their magnetic response can be tuned by a variation of the size of the particle material used. Since the atoms are located at the interface to a large degree (up to 40 %), the understanding of the surface functionalization and the interaction between them is of fundamental interest.
For the preparation of these nanomagnets there are two different approaches.
Bottom up: Synthesis of monodisperse, small particles (2 – 100 nm) by means of organo-metallic and gas phase synthesis or use of self organization processes on the atomic scale.
Top down: Standard thin film deposition techniques in combination with new lithographic techniques as diblock copolymer templates, biological templates (s-layer), alumina templates and nanosphere lithography.
The above mentioned topics are typically covered by researchers from different communities (nanoparticles, thin film magnetism, high resolution imaging, biologic or polymer templates) and therefore the symposium aims at providing an interdisciplinary communication and discussion forum.
1. Magnetic nanoparticles
The investigations of magnetic nanoparticle are mainly addressing materials with relevance to storage technology. These are high anisotropy materials like 4f/3d and L10-ordered FePt nanoparticles. By means of organo-metallic synthesis large quantities of these particles are prepared in colloidal suspensions with a high degree of monodispersity. Such suspensions are used for the periodic arrangement of the nanoparticles on a substrate. The major drawback is however that in order to achieve the L10-order a post deposition annealing step is required. This leads to a sintering of the adjacent particles. Many approaches have been tried in order to reduce the annealing temperature and thereby circumvent the problem of sintering. One approach is the gas phase preparation of such nanoparticles where the thermal treatment can be performed already before deposition. However, no regular arrangement is achieved so far. Similar problems are also inherent to embedded nanoparticles. In the interface between nanoparticles and matrix material plays an important role. Although there are a number of different concepts the technological requirements could not be fulfilled simultaneously so far.
2. Self-organized nanostructures
An alternative approach is the so-called bottom-up approach. Step edges or dislocation networks on single crystal substrates are used for a preferential positioning of atoms during film deposition. Depending on the deposition conditions islands of compact or fractal shape, nanowires or threedimensional islands can be prepared. The magnetic properties of these extremely small nanostructures are the central topic within this session. A detailed analysis of the structure and morphology of these nanostructures is extremely important in order to correlate magnetic properties with single step edge or island atoms.
3. Lithographically prepared nanostructures
In order to push the limits to smaller sizes in recent years the wavelength for conventional lithography has been decreased successively. These techniques become increasingly difficult and expensive at a wavelength of 157 nm since this light is already absorbed by air and thus the lithography has to be performed in vacuum. Therefore alternative approaches have been evaluated. In this session the structural and magnetic properties of nanostructures prepared by novel lithography techniques, like diblock copolymer templates, biological templates, nanosphere lithography and alumina templates, are presented.
4. Novel complex systems
Complex magnetic structures can be tailored due to the use of magnetic building blocks. A variation of composition leads to a modification of magnetic properties like magnetic anisotropy, magnetization or exchange coupling which cannot so easily be achieved by conventional film deposition techniques. The surface of the particles can be controlled and functionalized. These complex systems cover magnetic spheres, carbon nanotubes filled with magnetic material and micelle structures.