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Group of Amorphous, Nanocrystalline and Nanocomposite Materials

L. Kraus, F. Fendrych, O. Chayka, P. Kocián

Our group is involved in the research of new magnetic materials based on 3d metals. They are either amorphous or nanogranular materials with extraordinary, mainly soft magnetic, properties.



Research:

  • Metallic glasses

    • Amorphous metals (metallic glasses) are artificial metallic materials with disordered atomic structure. They exhibit some interesting properties, such as, high yield strength, corrosion resistance, high electrical resistivity etc. Ferromagnetic metallic glasses show also excellent soft magnetic behaviour. We have been engaged in the basic research of magnetic metallic glasses since 1975. Mainly the influence of atomic structure on induced magnetic anisotropy and magnetoelastic properties had been studied. Nowadays we are focused mainly on applied research and application of amorphous magnetic materials in technical practice.

    		 M-gauge

    Magnetoelastic strain sensor for civil engineering constructions and geotechnical applications.


  • Nanocrystalline materials

    • There has been a large interest in nanocrystalline ferromagnetic materials since 1988, when the nanocrystalline alloys known as FINEMET were discovered. They consist of very fine crystallites (nanocrystals) of ferromagnetic metal embedded in an amorphous matrix. They are produced mainly by a controlled crystallization of metallic glasses with appropriate chemical compositions. Excellent soft magnetic properties of such materials are due to random orientation and small size of nanocrystalline grains together with strong exchange coupling between the grains. Our group has been interested in the research of nanocrystalline ferromagnets since 1990. Magnetic and magnetoelastic properties of nanocrystalline FeNbCuSiB, FeNbB and FeCoNbB alloys have been investigated.

    Schematic view of nanocrystalline structure


  • Nanocomposite materials

    • Nanogranular composites are similar to nanocrystalline materials. The ferromagnetic metallic grains are, however, separated by a nonmagnetic insulating matrix. This results both in interesting magnetic and also electric transport properties. Some nanocomposites with high content of magnetic 3d metals show excellent soft magnetic properties and high electrical resistivity, which can find wide applications in high frequency communications and computer technology. On the other hand, the nanocomposites with higher content of insulating component exhibit superparamagnetic behaviour and spin-dependent giant tunneling magnetoresistence. We have been investigating magnetic and electric transport properties of nanocomposite materials since 1998. Nanocomposite films are prepared by the plasma jet technique in our Plasma Jet Laboratory and by the pulsed laser deposition in the Dep. of Multilayer Structures.
    The goal of the research is to clarify the correlations between the magnetic properties, electric transport mechanisms, magnetoresistance and the structure of nanogranular materials.
    Structure of a nanocomposite film.   


    Spin dependent tunneling            
    magnetoresistence                


    Experimental equipment:

    • Quasi-static hysteresis loops tracer. PC controlled device for measurement of hysteresis loops on open specimens (maximum field: 75 mT, sensitivity: 10-7 Vs);

    • 2 radiation furnaces for heat treatment of samples (up to 700°C) in magnetic field (up to 0.5 T) and under mechanical strain, in the air, vacuum or Ar atmosphere, PC controlled, working space: Æ20 ´140 mm;

    • Equipment for measurement of magnetoelastic properties of amorphous and nanocrystalline ribbons (magnetostriction constants, DE-effect);

    • Device for investigation of giant magnetoimpedance in ribbons, wires or thin film samples (maximum magnetic field: 75 mT, frequency: 0 - 15 MHz);

    • Plasma Jet Laboratory for deposition of magnetic films.



    Plasma Jet Laboratory:

    UHV equipment for the deposition of magnetic films. Plasma originating from the hollow-catode-discharge sputters the mouth of the nozzle supplying the working gas into the vacuum chamber. The sputtered material (after a possible chemical reaction with the reactive component of working gas) deposits on the substrate placed above the nozzle.
            • Kryopump COOLVAC 1500 (1500 l/s);
            • Turbomolekular pump TMU 261 (200 l/s);
            • predeposition vacuum 3 ´10-7 Pa;
            • working atmosphere Ar, Ar + N2, Ar + O2.


    Cooperation:

    Our group has close collaboration with other research groups in the Institute of Physics ASCR, Czech Republic and abroad:


        M a i n t a i n e d   b y 
     M i c h a l    R a m e s    (ramesm@fzu.cz)
    Last update: Aug 25 2010
    2010 © Dept. of Magnetism and Low Temperatures