Accreditation evaluation report
Activities of the Institute of Experimental Physics SAS in Kosice, during years 1999-2002, were directed mainly at the basic research in condensed matter and materials, subnuclear physics, space physics and biophysics. Results achieved by the institute during considered time period represent scientific research activities of its departments (Department of Magnetism, Department of Low Temperature Physics, Department of Metal Physics, Department of Subnuclear Physics, Department of Space Physics, Department of Biophysics, and Department of Theoretical Physics) and are presented in the following parts of this document. Taking into account the fact that majority of the achieved results was published in leading (top) international scientific journals, we may right away say, that the research in the institute in relevant fields corresponds to the current trends and fulfils all domestic and international criteria for relevance, exactness and quality of scientific work.
a)Research status
Department of magnetism
The present study in area of magnetism is engaged in comprehensive studies on the physical properties of nanocrystalline and amorphous ferromagnetic materials, ferrofluids and their composites with superconductive particles and liquid crystals, fine magnetic properties, organometalic complexes, high-Tc superconductors and intermetallic compounds containing f-element with interesting properties at low temperatures like heavy-fermion behaviour and heavy-fermion superconductivity
The relationship between microstructure and magnetic properties has been investigated in the nanocrystalline alloys based on Fe-M-B-(Cu), where M=Nb, Mo, Ti, Cr, where the size and volume fraction of grains has been modified by variation of composition and heat treatment procedure. It was found that except of the size effects (sizes of grains and intergramular distances) the significant role in the determining the soft magnetic characteristics of these systems is played by chemical and magnetic changes in the amorphous residual matrix during the crystallization process.
Magnetic properties of nanocrystalline alloys with composition Fe80.5Nb7B12.5 and Fe73.5Nb4.5Cr5B16Cu1 were studied in the temperature range 1,5 – 300 K. The main emphasis has been focused on the hysteresis loops, initial permeability and magnetostriction measurements. An unexpected rapid magnetic hardening has been observed below 50 K. We have shown that the low temperature hardening in FeNbB goes along with the strong irreversibility between field-cooling and zero-field cooling magnetization at low fields, which develops below 50 K. A slow relaxation of magnetization on the macroscopic time scale is confirmed by magnetization creep experiments. A rather large value of the microscopic relaxation time τ0=1.1×10-5 s accounts for a cluster-glass nature in our system. The results are discussed within a model that take into account the presence of weakly magnetic Nb-rich shells around the nanocrystalline grains. A detailed analysis of 3 D neutron depolarization studies together with the experiments obtained by cooling the samples in and without presence of external field have revealed the presence of exchange anisotropy effects at low temperatures.
The Burylov and Raikher's theory of thermotropic ferronematics was verified using the observations of structural instabilities of nematic liquid crystals doped with fine magnetic particles (ferronematics) in external magnetic and electric fields. In frame of this theory the anchoring energy of liquid crystal molecules on magnetic nanoparticles surfaces and the parameter determining the type of anchoring (soft or rigid) were calculated using the experimental results.
The light induced thermo diffusion in magnetic fluids (carrier = water, oil, kerosene) and consecutive self-diffraction were investigated, the phenomenon was theoretically described and a method for the calculation of the magnetic particles size distribution from obtained experimental results was developed. The self-structuralization of the colloidal particles concentration in magnetic fluid exposed to intensive illumination was observed, what substantiated the assumption about the negative value of the Soret constant in studied magnetic fluid.
The main results achieved in the area of the applications of magnetic fluids in biomedicine and biotechnology are the immobilization of several clinically important proteins and enzymes (bovine serum albumin (BSA), glucose oxidase, streptokinase, chymotrypsin, trypsin, dipase) onto magnetic particles using carbodiimide as a coupling agent and the determination of the optimum conditions of immobilization. The results obtained from the immobilization of enzyme trypsin to magnetic particles were consequently used for the determination of selected xenobiotics with magnetic particles – modified trypsin. The assays based on the specific enzymes immobilized on magnetic carriers could be also used in magnetic separation processes. The selection of the enzymes used for such assays depends upon the type of the analyzed compounds and on the sensitivity of the enzyme against them.
The main focus was the study of cooperative phenomena in cooperative systems containing 4f and 5 f metal in order to contribute to understanding of such phenomena as heavy fermion behavior, spin fluctuations, and long distance magnetic ordering. We studied crystal structure, magnetic and electronic properties of single crystals of intermetallic compounds and polycrystalline powders of Prussian blue analogs. We focus to the study of manifestations of itinerant and localized magnetism in these materials. An attention is paid to the study of magnetic excitations, magnetic structures and crystal field schemes. The nuclear and magnetic structures of U3Al2Si3 have been investigated by means of polarized and unpolarized neutron diffraction for single crystals. A polarized neutron study of the magnetization induced by applied fields above Tc shows marked anisotropy and makes it likely that it is this strong local anisotropy of the U3 ions which leads to the non–collinearity of the magnetic structure. Positive muon spin relaxation measurements performed on the ferromagnet UGe2 reveal, in addition to the well–known localized 5f-electron density responsible for the bulk magnetic properties, the existence of itinerant quasistatic magnetic correlations. Their critical dynamics is well described by the conventional dipolar Heisenberg model. These correlations involve small magnetic moments.
A substantial attention was paid to sample preparation. Rare–earth ferricyanides RE[Fe(CN)6]. 4H2O (RE=Ce,Pr,Sm,Gd,Dy and Ho); Prussian blue analogues M[Fe(CN) 5NO].x H2O (M=Fe, Co and Ni), commonly known as nitroprussides; new hexacyanomanganates Pr[Mn(CN) 6].4H2O and U[Mn(CN) ]6.5H2O; vanadium chromicyanides V[Cr(CN) 6].7H2O and (VO)3[Cr(CN)6]2.4H2O have been synthesized. The existence of magnetically ordered state in U[Mn(CN)6.nH2O with transition temperature Tc=36.8 K was confirmed. The presence of water molecules in two different positions in rare-earth based hexacyanocomplexes was confirmed by means of NMR and Moessbauer spectroscopy. This fact leads to the existence of isolated spin clusters in investigated compounds and therefore strongly influences resultant magnetic properties.
The study in area of high temperature YBaCuO bulk superconductor was devoted to influence of crystal defects on the microstructure. Last years we focused our research activity on the influence of Ag, Pt, Zn and Ce additions on the microstructure of single– grain YBa2Cu3O7/Y2BaCuO5 (123/211) bulk superconductors prepared by top seeding melt growth process. The processes leading to homogeneous distribution of 211submicron particles (pinning centres) in these superconductors and characterisation of mechanisms of formation cracks during crystallisation and another thermal treatments were developed.
Department of low temperature physics
The Department of LTP belongs together with the Institute of Physical Sciences of the Faculty of Science of the P.J. Safarik University to the club of approx. 20 laboratories, which are able to cover the area of low temperatures down to below 1 mK. These two groups received in 2002 the status Center of Excellence of the SAS with the name Center of Low Temperature Physics. The LTP department collaborates with US Steel Kosice, it performs expertise in vacuum and low temperature technique and receives sponsored liquid nitrogen. Low temperature physics is a revolutionary area where new conceptions are created. It enables to study quantum matter, strongly correlated systems as superconductors, superfluid 3He (the most complicated macroscopic subject), modern magnetic materials, heavy fermion systems. The activities of the department can be divided as follows:
1) Exotic superconductivity
2) Superfluid phases of helium 3
3) Strongly correlated electron systems
4) Intermetallic compounds based on rare earth
1) (Ba,K)BiO2: For the study of upper critical fields we have suggested anew non-dissipative method – magnetotunneling spectroscopy. This method is sensitive to the spatially averaged superconducting order parameter, which has anon zero value also when the superconductor is in the partially resistive state as aconsequence of vortex melting. By this method we have obtained temperature dependencies of the upper critical field of (Ba,K)BiO3 as well as of other systems, which are in agreement with the BCS theory, but in acontradiction with the results of the measurement by magnetoresistance.
The above-mentioned method of magnetotunneling spectroscopy we have applied on the same high quality crystal (Ba,K)BiO3 together with thermodynamic magnetic and transport measurements. Thus, we have found that the phase transition measured by the specific heat – HCp is different from that measured by magnetotunneling spectroscopy - HΔ = Hc2 . HCp represents aphase transition of unknown origin in the system of superconducting vortices.
MgB2: The Physics Today issue of January 2002 had declared the discovery of superconductivity in MgB2 among the five most important discoveries of the year 2001. One of the reasons is its application potential as apossible replacement for NbTi or Nb3Sn. The new fundamental physics is another reason. Our group has shown the first spectroscopic evidence of the new type of multiband/multigap superconductivity in this system.
Intrinsic Josephson junctions: The temperature dependence of the interlayer electrical resistance as well as the isothermic magnetoresistance in high temperature cuprates has been asubject of great interest, particularly for their anomalous behavior. The interpretation is abasement of various novel theories of high temperature superconductivity. We have recently studied the interlayer transport in low temperature strongly anisotropic superconductor (LaSe)1.14(NbSe2) without any pseudogap. We have shown that the existence of an anomalous expressive peak in the isothermic magnetoresistance is connected with the tunneling character of the charge transport between superconducting layers of (NbSe2) which are coupled by Josephson tunneling via the interlayer of insulating LaSe. Thus the system represents aseries of intrinsic Josephson junctions. This effect must be considered also in the mentioned high temperature superconducting cuprates. The dimensional transitions in the behavior of vortices are under study in this kind of systems with the intrinsic Josephson junctions.
2) Low frequency spin excitations - spin precessing waves - in superfluid 3He-B were studied by the method of homogeneously precessing domain (HPD). It was shown that to these precessing waves corresponding oscillation modes of the HPD can be used as a tuned quantum resonance amplifier, which enables to measure very small magnetic fields with a resolution of 10-7.
In frame of the collaboration with University of Lancaster we continued the study of properties of the interface between A and B phases of superfluid helium-3. Thermal oscillations generated by a moving A-B interface were observed. Simultaneously the temperature dependence of the critical magnetic field of the A phase was determined.
In parallel with the above experiment, studies of primary and secondary nucleation of A and B phases were made. A few nucleation scenarios were developed and checked. The experiment has shown that as outside stimulus at about 150 K the most effective was a simple mechanical pulse, not the application of neutron or gamma radiation as it was expected before.
As methodical results in our lab in Kosice can be considered the implementation of vibrating wire thermometry in the temperature range below 300 K, the improvement of pulse and continuous NMR methods, the realization of the “fixed-point” temperature device for T < 1 K, and the modifications of the nuclear demagnetization apparatus which enabled to cool superfluid helium below 0.2 TC.
3) SmB6: The experimental studies of transport, magnetic and thermal properties of the heavy fermion semiconductor SmB6 have pointed to three experimental scales in the excitation spectrum of this compound, which correspond to various electron mobility regimes. It was shown that the energy gap of this material shows features of a pseudogap, and that the electronic states at the Fermi level have an enhanced nature.
UPt3: Based on magnetization measurement of this heavy fermion superconductor it was shown that the superconductivity in this compound is unconventional. Moreover, below about 20 mK antiferromagnetic ordering was observed.
4) HoB12: Magnetization and neutron studies of this material has revealed three magnetic phases in the diagram magnetic field vs. temperature.
RENi5 (RE - rare earth element): Microcontact studies of these compounds were performed. The splitting of crystalline electric field levels in magnetically ordered state directly by this method was observed for the first time.
RECu5: The electron-quasiparticle interaction in this system was investigated by point-contact spectroscopy. The electron transport, magnetic properties and point-contact spectroscopy were investigated in DyCu5, which shows two phase transitions at low temperatures.
Department of metal physics
The activities of the department of metal physics are concentrated on the experimental study of metals, mainly their mechanical properties in the wide temperature range. The scientific interest is focused on the homogeneous and inhomogeneous plastic deformation of amorphous metals. Creep and creep recovery processes in these materials are studied in detail. The fractography of amorphous alloys is often used for describing the structure of the materials and their failure mechanisms. Mechanical testing, fractography, thermomechanical investigations and structure examinations are the basic experimental methods of investigations. New numerical methods for calculating of activation energy spectrum from isothermal and non-isothermal experimental measurements were used. The crystal structure and the relation between the structure and other physical properties (mainly magnetic) of materials have been studied by means of diffraction techniques. New mathematical methods of measured data processing, which enable investigation of the crystal structure in details, were used.
We performed the precise creep measurements of a Ni77.5Si7.5B15 and Co70Fe5Si15B10 metallic glass ribbons. The obtained results indicate that plastic flow at low stresses (12 < 307 MPa) is clearly non-Newtonian with the strain rate sensitivity coefficient close to 1. This is a consequence of stress dependence of structural relaxation parameters e.g. number of relaxation centers and their effective volume.
The of creep behaviour study of bulk metallic glass Zr52,5Ti5Cu17,9Ni14,6Al10in wide range of heating rates well below and in the vicinity of the glass transition temperature Tg were performed. . It was shown that in all cases the shear viscosity rapidly decreases with temperature. However, the characteristics of the decreasing depend strongly on the temperature range.
The creep recovery process in finemet type amorphous alloys has been analyzed using the method for calculation the relaxation time spectra. The influence of structural relaxation and temperature on the spectra shape has been studied.
The failure processes study of bulk amorphous and nanocrystaline metallic alloys showed that the meniscus instability process is dominant failure mechanism similar as in the case of amorphous ribbons. Some observed morphological differences are explained as the influence of different geometric conditions during the nucleation, growth and coalescence of voids.
A set of nanocrystalline samples of finemet composition Fe73.5Cu1Nb3Si13.5B9 prepared by the spinning wheel technique, with different annealing parameters within the crystallization temperature region determined as a result of the thermomechanical analysis were investigated by means of x-ray diffraction methods. The kinetics of amorphous to nanocrystalline phase transition of the alloy was examined by observing the development of nanocrystalline component and by the estimation of the average size of the coherent regions.
The structure and magnetic properties of microcrystalline Fe93.5Si6.5 and Co70.3Fe4.7B25 ribbons prepared by melt spinning method and the influence of long milling process time was studied. A Fe phase of the Fe93.5Si6.5 alloy was detected by both XRD and Mössbauer spectroscopy, while DO3 structure of a Fe-Si phase with various number of Fe surroundings atoms was detected only by Mössbauer spectroscopy. The Co3B phase was identified in Co70.3Fe4.7B25 sample by x-ray diffraction and two different Fe-rich phases which probably correspond to the two different symmetrical nonequivalent positions of Co(Fe) atoms in the Co3B unit cell was detected by Mössbauer spectroscopy. The experimental data enabled to describe the real structure of the samples.
The Re[Fe(CN)6] .nH2O ferricyanides where RE=Pr, Sm, Gd, Dy and Ho have been prepared. These compounds were characterized structurally and magnetically. The details of the crystal structure were determined using x-ray diffraction technique by means of the Rietveld structure refinement method. The crystal structure of the compounds was refined in according to hexagonal model (space group P 63/m). The details of the crystal structure were investigated by means of the neutron scattering.
Department of subnuclear physics
Experimental activities of the department are oriented towards our participation in the scientific programmes of the top laboratories for the subnuclear physics: DESY Hamburg, CERN Geneva and Fermilab Chicago.
H1 experiment at DESY is oriented to study of the p-e collisions at energies of cca. 300 GeV in centre of mass system. Among the most important results are the precise mesurement of the cross section of the deep inelastic scattering in e-p collisions at the four momentum transfer squared 1.5 Q2 150 GeV2 and Bjorken-x values of 3 10-5 x 0.2 using a new instrumentation of the H1 detector, measurement of the jet production in the deep inelastic scattering at lasrge Q2 , used for the precise determination of the strong interaction coupling constant and gluon distributions in proton. Other topics of interest were the search for the rare and exotic states, tests of the quantun chromodynamics, the study of the vector meson production, photoproduction and the real and virtual photon structure. Our group took part in various methodological strudies and H1 upgrade programme.
The ATLAS experiment, planned for the LHC accelerator being built at CERN, is now in the construction and building stage. Our group participates in technical and methodological tasks, and is responsible for the design, development and construction of the hadronic end-cap calorimeters (HEC). Among the most imortant achievements we may mention successfully developed and tested calibration system, development and tests of the so called cold electronics and the front-end readout boards for the ATLAS calorimeters, finishing of the development and production of some hardware compoments, as well as realization of the comparative analysis of the GEANT-3.21 and GEANT-4 simulation packges for the hadronic showers.