Detailed tasks
Investigation of magnetic nanostructures
(B. Bulka, J. Barnas, S. Krompiewski, A. Paja, S. Robaszkiewicz, E. Zipper)
The studies are devoted to electric and magnetic mesoscopic systems of peculiar geometry, e.g. carbon nanotubes, ring-shaped systems as well as single and coupled quantum dots. These structures have been recently intensively studied, and some of them have already found practical applications (flat displays, portable field-effect based Roentgen apparatus, current rectifiers, chemical and magnetic-field sensors, single electron transistor etc.) In particular, transport through the aforementioned nanostructures, depending of their internal structure, the sort of electrodes and interface conditions, will be dealt with. In the case of ferromagnetic electrodes the attention will be concentrated on the giant magnetoresistance effect and spin polarization of electrical current. In the weak nanostructure/electrode coupling limit the problem reduces to tunneling and the so-called Coulomb blockade mechanism should be included together with higher order (co-tunneling) processes. Other, very exciting problems addressed in the project, are (i) response of nanostructures to external magnetic field, (ii) the proximity effects in nanostructure/superconductor systems, as well as (iii) the influence of structural disorder, spin-orbit interaction and electron spin relaxation on the electron transport.
Surface effects in novel magnetic materials
(H. Puszkarski)
The interest in artificial structures has increased significantly in the last decade. For example, an extremely keen interest has been aroused by structures referred to as "photonic crystals". These are periodic structures composed of two types of transparent dielectric materials forming a "macrocrystal", with lattice constant ranging from 0.1 mm to 1 cm, showing a "photonic" energy gap, in which light propagation is forbidden. Photonic crystals have been intensively studied recently, both theoretically and experimentally, and the promising research prospects in this field inspire us to take up a theoretical research of macrocrystals topologically equivalent to the photonic structures, but composed of different magnetic materials. These structures can be called, by analogy, "magnonic crystals". As magnetic materials are extensively used in technology, these new materials can be expected to find perspective applications as well.
Properties of thin magnetic films and multilayers
(T. Balcerzak, L. Wojtczak)
The studies concentrate on the influence of interfaces and surfaces on magnetic properties of bi- and tri-layers, and the role of roughness effects. The particular attention is paid to magnetic anisotropy effects in the context of spin-wave resonance spectra. Transport properties in magnetic multilayers, including giant magnetoresistance are also addressed.
Electron and hole transport in the doped transition metal oxides
(A. Lehmann-Szweykowska, J. Barnas, R. Wojciechowski, R. Micnas)
There have been a number of recent experiments showing a sharp drop of anisotropic magnetoresistance in calcium-doped yttrium-iron garnet thin films. A theoretical explanation is proposed concerning the spin dependent charge transfer in the yttrium-iron garnets doped with valence-uncompensated ions. Within the framework of the model of tetrahedral and octahedral iron-oxygen clusters, we analyze the influence of the external magnetic field both on the superexchange coupling between spins attached to the orbital ground eigen-states of the clusters as well as on the spin-conditioned charge transfer between those of the different and the same symmetry.
First principles computations
(A. Jezierski, S. Uba)
Investigations of physical properties of solids are carried out by ab initio methods, in particular the spin-polarized LMTO method is used to calculate: band structures, partial densities of states, spin and orbital magnetic moments, total energy, optical and magneto-optical properties. The calculations for various directions of magnetization make it possible to find anisotropy of spin- and orbital-moments as well as the magnetocrystalline anisotropy. Extended advanced calculations of complex systems (up to 100 atoms per unit cell) with the use of supercell technique enable one to model the microstructure of interface layers as well as short and long range chemical disorder in alloy systems.
Intermetallic compounds and 4f- and 5f- metal based alloys
(J. Frackowiak, D. Kaczorowski, Cz. Kapusta, A. Kowalczyk, K. Krop, R. Troæ, A. Szytula, A. Slebarski, A. Zygmunt)
Magnetism and other phenomena associated with the 4f and 5f electrons have been an important subject of studies for a few decades. The current interest concentrates on electronic structure and magnetic properties of strongly correlated electron systems, which are known to exhibit a variety of exotic behavior, like Kondo-lattice, heavy-fermions, non-Fermi liquid and unconventional superconductivity, as well as giant magnetocrystalline anisotropy and so on. The goals of the present activities are to search the mechanism lying behind these abnormal phenomena, and look for prospective applications. For instance, thermoelectric materials can be used for power generation or refrigeration using the direct conversion of heat and electricity.
Another important field of the research is concentrated on determination of magnetic properties (including magnetic structure) and electronic structure of ternary rare-earth based compounds. The aim of this study is to find mutual correlations between electronic and magnetic structures. Particularly interesting compounds are those with magnetic moments localized on the transition metal atoms. Interesting magnetic properties and electronic structure together with possible practical applications make intermetallic compounds a subject of intensive studies world-wide.
Magnetic thin films and layered metallic structures
(L. T. Baczewski, T. Blachowicz, M. Wolny-Kaczmarek, F. Stobiecki, T. Stobiecki, S. Uba)
Since the giant magnetoresistance effect was discovered more than a decade ago it has attracted a lot of physicists and material scientists due to its potential application ability as magnetic field sensors and recording heads. Therefore the main aim of the present activity is to obtain layered structures exhibiting large GMR values accompanied by low magnetic saturation or switching fields. The specific problems in the case of GMR materials include the influence of sublayer topology, morphology and thermal treatment on the amplitude and the field sensitivity of the GMR effect. One of the goals of the activities is understanding of magnetism and spin dependent electronic transport in thin films and multilayers which in the form of nanopattern elements create: magnetic sensors, M-RAM 's (Magnetic Random Access Memory) and magnetic recording devices (e.g. heads, HDD-discs and magneooptical discs).
Our interest in the magnetic heterostructures concentrates on relationship between microstructure and magnetic properties including low-dimmensional magnetic nanostructures. Therefore the complex studies of artificial nanostructures such as:
- magnetic heterostructures (granular films or layered granular structures)
- soft magnetic nanocrystalline multilayers
- low-dimensional magnetic nanostructures (emphasizing the relationship between microstructure and magnetic properties)
