• Technische Universität Dresden, Germany
• University of Twente, The Netherlands
• Max Planck Institute for Solid State Research, Stuttgart, Germany
• CNRS-Thales, Orsay, France
• Insitut for Theoretical Physics, RWTH, Aachen, Germany
• Universität Regensburg, Regensburg, Germany

Our "nanogallery" based on recent publications

Anomalous, spin, and valley Hall effects in graphene deposited on ferromagnetic substrates   
A. Dyrdał and J. Barnaś, 2D Mater. 4 (2017) 034003
DOI: 10.1088/2053-1583/aa7bac

Spectral properties and the Kondo effect of cobalt adatoms on silicene
I. Weymann, M. Zwierzycki, and S, Krompiewski, Phys. Rev. B 96 (2017)115452.
DOI: 10.1103/PhysRevB.96.115452

Edge magnetism of finite graphene-like nanoribbons in the presence of intrinsic spin-orbit interaction and perpendicular electric field.
S. Krompiewski, Nanotechnology 27, (2016) 315201
DOI: 10.1088/0957-4484/27/31/315201

Spin-orbital and spin Kondo effects in parallel coupled quantum dots
D. Krychowski and S. Lipiński, Phys. Rev. B 93 (2016) 075416
DOI: 10.1103/PhysRevB.93.075416

Transport through graphenelike flakes with intrinsic spin-orbit interactions
I. Weymann, J. Barnaś, and S, Krompiewski, Phys. Rev. B 92 (2015) 045427
DOI: 10.1103/PhysRevB.92.045427

I. Weymann, S. Krompiewski, and J. Barnaś, J. Nanosci. Nanotechnol. 12 (2012) 7525.
DOI: 10.1166/jnn.2012.6532

Effect of the attachment of ferromagnetic contacts on the conductivity and giant magnetoresistance of graphene nanoribbons,
S. Krompiewski, Nanotechnology 23 (2012) 135203,
http://iopscience.iop.org/0957-4484/23/13/135203/

Electronic transport through side-contacted graphene nanoribbons: effects of overlap, aspect ratio and orientation,
S. Krompiewski, Nanotechnology 22 (2011) 445201,
http://iopscience.iop.org/0957-4484/22/44/445201

Spin Dependent Transport through a Carbon Nanotube Quantum Dot in the Kondo Regime,
S. Lipiński, D. Krychowski, in Electronic properties of carbon nanotubes (ed. J. M. Marulanda, Intech 2011),
http://www.intechopen.com/books/electronic-properties-of-carbon-nanotubes

Spin polarized current and shot noise in carbon nanotube quantum dot in the Kondo regime,
S. Lipiński, D. Krychowski, Phys. Rev. B 81 (2010) 115327,
http://prb.aps.org/abstract/PRB/v81/i11/e115327

Theoretical studies of spin-dependent electronic transport in ferromagnetically contacted graphene flakes,
S. Krompiewski, Phys. Rev. B 80 (2009) 075433,
http://prb.aps.org/abstract/PRB/v80/i7/e075433

Transport through single-wall metallic carbon nanotubes in the cotunneling regime,
I. Weymann, J. Barnaś, S. Krompiewski, Phys. Rev. B 78 (2008) 035422,
http://prb.aps.org/abstract/PRB/v80/i7/e075433

Theoretical prediction of perfect spin filtering at interfaces between close-packed surfaces of Ni or Co and graphite or graphene,
V.M. Karpan, P.A. Khomyakov, A.A. Starikov, G. Giovannetti, M. Zwierzycki, M. Talanana, G. Brocks, J. van den Brink, and P.J. Kell
Phys. Rev. B 78 (2008) 195419,
http://prb.aps.org/abstract/PRB/v78/i19/e195419

Research objectives

We are researching the physics of nanostructures aiming both at modeling and understanding of their properties. The research concerns fundamental problems important also in the context of practical application in nanotechnology (including spintronics and spin-calorytronics). We focus  in particular on the spin transport, electron correlations (Hubbard-type, Coulomb blockade, Kondo effect), structural imperfections (boundary effects, interfaces, defects, admixtures, ripples, etc.). The development of the theory describing the processes involving both charge and spin degrees of freedom as well as heat transfer in the nanoscale is essential for the creation of future generations of innovative electronic  devices. These should realize the double goal of improved performance and energy efficiency, important for environment protection and thereby economic growth.

Research profile

Theoretical studies of electronic, magnetic and magneto-thermoelectric phenomena in nanoscopic systems. In particular, intensive investigations on carbon nanostructures (nanotubes and graphene), graphene-like systems and quantum dots. A wide range of computational methods is used, starting from analytical methods and preliminary analysis by means of simple programs (Mathematica and so on) through the tight-binging method up to advanced first principle methods. In transport studies, the Green’s function technique is used in combination with the Landauer-Büttiker and Keldysh formalisms.

Research projects

• Project 6 PR UE - Carbon nanotube devices at the quantum limit CARDEQ (2006-2009), head - Prof. S. Krompiewski
• Projckt MNiSW - Carbon nanotube devices at the quantum limit SPUB (2006-2009), head - Prof. S. Krompiewski
• Supervisor’s Project MNiSW – Analysis of the influence of strong correlations on electronic transport in nanostructures(2009-2010), supervisor – Dr. habilit. Lipiński, Prof. IFM PAN  (Ph.D student. – BSc.  eng. D. Krychowski)
• Project MNiSW – The effect of topology, interfaces and electron correlations on the charge and spin transport in graphene (2010-2013), head - Prof. S. Krompiewski
• Project NCN - Graphene-based (and similar) nanostructures for spintronics and spin caloritronics. Theoretical studies (2014-2017), head - Prof. S. Krompiewski

Scientific achievements  

• Studies on the spin Hall effect in one- and two-layer graphene. Demonstrating that in the presence of perpendicular electric field, there is a phase transition from the topological insulator phase to the ordinary insulator phase.
• Performing model shot noise computations for a double magnetic tunnel junction. Theoretical predictions have been verified by comparison with experimental results for Fe/MgO/Fe/MgO/Fe.
• Studies on the effect of the transverse magnetic anisotropy on the spin switching of a single atom or a single magnetic molecule by current. It has been shown that the quantum tunneling of magnetization occurs in certain resonance fields when at least one electrode is ferromagnetic.
• Analyzing a graphene bilayer it was shown that beyond the van Hove singularity region the impurity spin polarization  for SU(2) symmetry  is opposite to the bilayer polarization, whereas it is the same for SU(4). Close to the singularity, a reversal of the impurity magnetic moment is possible.
• Examining the effect of electrode/graphene-structure interfaces, and the effect of electron edge states (including possible appearance of magnetic moments) on the electronic transport.
• Development of an effective recursive method (knitting) to study a multi-electrode electronic transport. A strong spin-valve type effect has been found in the case of four electrodes located in the centers of the square flake.
• Based on ab initio band structure computations combined with a few complementary techniques for analyzing many-body effects, the Kondo effect for cobalt adatoms placed on a graphene zigzag ribbon has been examined. In particular, the competition of spin and orbit degrees of freedom, and the impact of relevant details of both the electronic and magnetic structures of the ribbons have been thoroughly discussed. Similar computations have also been performed for a quasi two-dimensional (buckled) silicene layer with a cobalt adatom.
• It has been shown that magnetic moments at zigzag edges of graphene ribbons may be considerably weakened or completely suppressed after application of external current electrodes. The effect strongly depends on electronic nature of the graphene/electrode interface and on the distance between the electrodes.
• The following structural imperfections have been also taken into account: the aforementioned edge effects, inter-grain boundaries in polycrystalline carbon nanostructures, and the so called antidots (empty regions).

In 2009-2017, 5 research projects were carried out (including 1 European and 1 bilateral “Harmonia” projects). The projects were devoted to studies of physical phenomena in carbon nanotubes, graphene and in graphenelike nanostructures of potential importance for innovative applications in nanoelectronics and spintronics.



Keywords:

intermetallic compounds, amorphous materials, nanocrystalline alloys, magnetism, magnetocaloric effect, thermoelectric power, Kondo lattices

The Laboratory is engaged in the complex studies of new magnetic materials such as:

• rare earth intermetallic compounds
• strongly correlated electron systems
• nanocrystalline magnetic alloys
• amorphous magnetic ribbons
• thin films of rare earth and transition metals
• metallic multilayers
• rare earth manganite
• magnetic nanostructures

Research aims

Experimental studies supported by the theoretical interpretation in the area of the strongly correlated electron systems with main emphasis on the Kondo lattices, systems with the impurity Kondo effect, fluctuating valence systems, spin glasses. Characterization of the glass forming ability of the amorphous alloys and the studies of the crystallization processes in the structurally metastable alloys. Search for new magnetocaloric and thermoelectric materials with parameters expected in applications.

Research profile

Preparation of the rare earth-based intermetallic compounds and alloys in a crystalline, nanocrystalline and amorphous form. Structural characterization (X-ray diffraction) and determination of the magnetic (magnetometry, dc and ac magnetic susceptibility), electrical (electrical resistivity, magnetoresistance, Hall effect), and thermal (specific heat, thermal conductivity, thermoelectric power) properties in a wide temperature range.

Scientific achievements

• A jump of material density was observed when changing the stoichiometry for Hf₁Cr₁Co₁₁B and Hf_0.5Cr_1.5Co₁₁B, which was correlated with a change of structure from amorphous to crystalline. Measurements have been carried out with a novel method, employing a confocal microscope, enabling measurements for samples with small volume [Śniadecki et al. Materials Characterization 132, 46 (2017)]
• Based on the measurements of the DC and AC magnetic susceptibility the magnetic phase diagram was determined for the series Ce(Cu_1-xNi_x)₄Mn. It shows a complex character, e.g. it indicates presence of regions with coexisting ferromagnetic and spin glass phases [K. Synoradzki, T. Toliński, Materials Chemistry and Physics, 177, 242-249 (2016)]
• Coexistence of two phases of Hf₂Co₁₁ was confirmed based on the XRD and thermomagnetic measurements of the alloy Hf₂Co₁₁B [A. Musiał et al. J. Alloys Compd. 665, 93 (2016)]
• The influence of the chemical and topological disorder on the magnetic properties of compounds based on the Pauli paramagnet YCo₂ has been observed and described [Z. Śniadecki et al., J. Appl. Phys. 115, 17E129 (2014), Z. Śniadecki et al., Appl. Phys. A 118, 1273 (2015), A. Wiśniewski et al., J. Alloys Compd. 618, 258 (2015)]
• Using semi-empirical models the glass forming ability of the transition metal based ternary systems has been determined. The ranges of stoichiometry promoting the alloys amorphization have been calculated [Z. Śniadecki, J. Alloys Compd. 615, S40 (2014)]
• Magnetic properties and parameters characterizing the magnetocaloric effect have been determined for ferrimagnets composed of two sublattices based on cobalt and rare earth element [Z. Śniadecki et al., J. Alloys Compd. 584, 477 (2014)]
• The mechanism of the amorphization of the alloys Y(Ce)-Cu-Al has been explained and the influence of the 4f electrons on the magnetic, transport, and thermal properties of these alloys has been described [B. Idzikowski et al., J. Non-Cryst. Solids 357, 3717 (2011), B. Idzikowski et al., J. Non-Cryst. Solids 383, 2 (2014)]
• For many cerium based compounds the influence of the crystal electric field on their physical properties has been determined. The research includes mainly the magnetic susceptibility, specific heat, and inelastic neutron scattering measurements [ Toliński et al., J. Magn. Magn. Mater. 345, 243 (2013)]
• For the first time the adiabatic temperature change and the influence of the grains size on the efficiency of the magnetocaloric effect in the Mn₅Ge₃ compound have been determined. For selected compounds of the series RNi₄M (R- rare earth, M - metalloid) the parameters characterizing the magnetocaloric effect have been extracted. [T. Toliński et al., Intermetallics 47, 1 (2014), Toliński et al., J. Alloys Compd. 523, 43 (2012)]
• Complementary studies of the isostructural series of compounds Ce(Cu_1-xNi_x)₄Mn_yAl_1-y enabled a construction of magnetic phase diagrams for four transformations between different ground states (ferromagnetic state, spin glass, fluctuating valence, heavy fermions) [K. Synoradzki et al., Phys.: Condens. Matter 24, 136003 (2012)]
• Magnetic susceptibility measurements in a wide temperature range (2-1000 K) supported by the interconfiguration fluctuation model (ICF) have shown a presence of the valence fluctuations between Yb³⁺ and Yb²⁺ for the compound YbNiAl This compound is not a heavy fermion system, which results from the determined small value of the electronic specific heat coefficient. [A. Kowalczyk et al., J. Appl. Phys. 107, 123917 (2010)]
• The temperature dependences of the thermopower have been determined and explained for the Kondo lattices CeCu₄M and for compounds exhibiting fluctuating valence CeNi₄M (M = In, Ga) [T. Toliński et al., J. Alloys Compd. 490, 15 (2010)]
• Apart from the experimental methods employed directly in the Magnetic Alloys Department, the carried out researches involve many complementary methods accessible in frames of the international cooperation (neutron diffraction, inelastic neutron scattering, synchrotron radiation)