A. Hamzic

University of Zagreb, Zagreb, Grad Zagreb, Croatia

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Publications (72)140.18 Total impact

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    ABSTRACT: We have in detail characterized the anisotropic charge response of the dimer Mott insulator $\kappa$-(BEDT-TTF)$_2$Cu$_2$(CN)$_3$ by dc conductivity, Hall effect and dielectric spectroscopy. At room temperature the Hall coefficient is positive and close to the value expected from stoichiometry; the temperature behavior follows the dc resistivity $\rho(T)$. Within the planes the dc conductivity is well described by variable-range hopping in two dimensions; this model, however, fails for the out-of-plane direction. An unusually broad in-plane dielectric relaxation is detected below about 60 K; it slows down much faster than the dc conductivity following an Arrhenius law. At around 17 K we can identify a pronounced dielectric anomaly concomitantly with anomalous features in the mean relaxation time and spectral broadening. The out-of-plane relaxation, on the other hand, shows a much weaker dielectric anomaly; it closely follows the temperature behavior of the respective dc resistivity. At lower temperatures, the dielectric constant becomes smaller both within and perpendicular to the planes; also the relaxation levels off. The observed behavior bears features of relaxor-like ferroelectricity. Because heterogeneities impede its long-range development, only a weak tunneling-like dynamics persists at low temperatures. We suggest that the random potential and domain structure gradually emerge due to the coupling to the anion network.
    07/2014;
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    ABSTRACT: (eds J. Heber, D. Schlom, Y. Tokura, R. Waser and M. Wuttig), Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim, Germany. „Bimetallic alloys as model systems for the growth of ultrathin metal oxide films.” Marco Moors, Séverine Le Moal, Jan Markus Essen, Christian Breinlich, Maria Kesting, Stefan Degen, Aleksander Krupski, Conrad Becker, Klaus Wandelt pages 181-183.
    The Nature Conference Frontiers in Electronic Materials; 06/2012
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    ABSTRACT: We have measured the Hall effect on recently synthesized single crystals of the quasi-one-dimensional organic conductor TTF-TCNQ (tetrathiafulvalene-tetracyanoquinodimethane), a well known charge transfer complex that has two kinds of conductive stacks: the donor (TTF) and the acceptor (TCNQ) chains. The measurements were performed in the temperature interval 30 K < T < 300 K and for several different magnetic field and current directions through the crystal. By applying the equivalent isotropic sample approach, we have demonstrated the importance of the choice of optimal geometry for accurate Hall effect measurements. Our results show, contrary to past belief, that the Hall coefficient does not depend on the geometry of measurements and that the Hall coefficient value is approximately zero in the high temperature region (T > 150 K), implying that there is no dominance of either the TTF or the TCNQ chain. At lower temperatures our measurements clearly prove that all three phase transitions of TTF-TCNQ could be identified from Hall effect measurements.
    Journal of Physics Condensed Matter 02/2012; 24(4):045602. · 2.22 Impact Factor
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    ABSTRACT: We study the extrinsic spin Hall effect induced by Ir impurities in Cu by injecting a pure spin current into a CuIr wire from a lateral spin valve structure. While no spin Hall effect is observed without Ir impurity, the spin Hall resistivity of CuIr increases linearly with the impurity concentration. The spin Hall angle of CuIr, (2.1±0.6)% throughout the concentration range between 1% and 12%, is practically independent of temperature. These results represent a clear example of predominant skew scattering extrinsic contribution to the spin Hall effect in a nonmagnetic alloy.
    Physical Review Letters 03/2011; 106(12):126601. · 7.73 Impact Factor
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    ABSTRACT: Using a combination of advanced characterization tools (positron annihilation spectroscopy, conductive-tip atomic force microscopy, and high-field magnetotransport), we have studied the extension, origin and properties of the high mobility electron gas (HMEG) generated by etching the SrTiO <sub>3</sub> surfaces with Ar <sup>+</sup> ions. Contrary to previous assumptions, we show that this HMEG is not confined to nanometric thickness but extends to a few micrometer from the surface. We discuss this unanticipated large spatial extension in terms of the striking large diffusion of oxygen vacancy-related defects.
    Journal of Applied Physics 06/2010; · 2.21 Impact Factor
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    ABSTRACT: We have carried out positron-annihilation spectroscopy to characterize the spatial distribution and the nature of vacancy defects in insulating as-received as well as in reduced SrTiO3 substrates exhibiting high-mobility conduction. The substrates were reduced either by ion etching the substrate surfaces or by doping with vacancies during thin-film deposition at low pressure and high temperature. We show that Ti vacancies are native defects homogeneously distributed in as-received substrates. In contrast, the dominant vacancy defects are the same both in ion etched crystals and substrates reduced during the film growth, and they consist of nonhomogeneous distributions of cation-oxygen vacancy complexes. Their spatial extension is tuned from a few microns in ion-etched samples to the whole substrate in specimens reduced during film deposition. Our results shed light on the transport mechanisms of conductive SrTiO3 crystals and on strategies for defect-engineered oxide quantum wells, wires, and dots.
    Physical Review B 01/2010; 81(14). · 3.66 Impact Factor
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    ABSTRACT: SrTiO3 becomes a high-mobility metallic conductor when doped with oxygen vacancies at low concentrations ( ≥ 1016 cm−3). We show that the vacancy concentration in the SrTiO3 single crystal substrates could be controllably tuned by changing the thickness of oxide films (deposited by pulsed laser deposition at high temperature and low oxygen pressure). The obtained variation in the carrier density strongly influences the transport properties. The quantitative analysis of the experimental results leads toward new and accurate strategies for the design of multifunctional oxide heterostructures for electronics and spintronics.
    Applied Physics Letters 01/2009; 94(1):012113-012113-3. · 3.79 Impact Factor
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    ABSTRACT: We present Hall effect measurements of two-leg ladder Sr14-xCaxCu24O41 (0⩽x⩽11.5). In these composite materials charge and spin ordering occur within chain and ladder subsystems. They have been investigated intensively during the last years because of their fascinating physical properties, especially after the discovery of superconductivity under pressure (for x>10). They are the first superconducting copper oxides (superconductivity occurs under pressure for x>10) without the CuO2 planes, characteristic for high-temperature superconductors. The question of charge dynamics and hole distribution between the ladders and chains is still open. Our Hall effect results show typical semiconducting behavior for x<10. The x=11.5 compound shows metallic behavior and our Hall effect results match qualitatively the behavior found in high-Tc cuprates. We have determined the effective number of carriers and its dependence on composition (x) and compared it to the number of holes in the ladders obtained by other experimental techniques at room temperature.
    Physica B Condensed Matter 01/2009; 404:385-388. · 1.28 Impact Factor
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    ABSTRACT: Systematic study of electrical resistivity of Hf_{100-x}Fe_x (x=20,25), Hf_{100-x}Cu_x (x=30,40,50), and Ti_{65}Cu_{35} metallic glasses has been done in the temperature range 0.3 K - 290 K, and in magnetic fields B <= 5 T. All Hf-base alloys are superconducting with T_c >= 0.44 K, which is well above T_c of pure crystalline Hf (0.13 K). From the initial slopes of the upper critical fields, (dH_{c2}/dT)_{T_c}, and resistivities we determined the dressed electronic densities of states, N_{\gamma}(E_F), for all alloys. Both T_c and N_{\gamma}(E_F) decrease with increasing x (Fe and Cu content). The results are compared with those for corresponding Zr-base metallic glasses and ion-implanted Hf films.
    Journal of Physics Condensed Matter 07/2008; · 2.22 Impact Factor
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    ABSTRACT: Ru1-xSnxSr2EuCu2O8 and Ru1-xSnxSr2GdCu2O8 have been comprehensively studied by microwave and dc resistivity and magnetoresistivity and by the Hall measurements. The ruthenium magnetic ordering temperature Tm is considerably reduced with increasing Sn content. However, doping with Sn leads to only slight reduction of the superconducting critical temperature Tc accompanied with the increase in the upper critical field Bc2 , indicating an increased disorder in the system and a reduced scattering length of the conducting holes in CuO2 layers. In spite of the increased scattering rate, the normal state resistivity and the Hall resistivity are reduced with respect to the pure compound, due to the increased number of itinerant holes in CuO2 layers, which represent the main conductivity channel. Most of the electrons in RuO2 layers are presumably localized, but the observed negative magnetoresistance and the extraordinary Hall effect lead to the conclusion that there exists a small number of itinerant electrons in RuO2 layers that exhibit colossal magnetoresistance.
    Physical review. B, Condensed matter 01/2008; 77(21). · 3.77 Impact Factor
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    ABSTRACT: We present Hall-effect measurements of two-leg ladder compounds Sr14-xCaxCu24O41 (0
    Physical review. B, Condensed matter 01/2008; 78(15). · 3.77 Impact Factor
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    ABSTRACT: Hall-effect measurements are presented on four heavy-fermion systems: UPt3, UAl2, CeAl3, CeRu2Si2. We show that the Hall effect is primarily due to skew scattering. At low temperature the Hall constant increases rapidly above its residual value and is associated with the development of skew scattering by fluctuations about the coherent state. At high temperatures, in the regime of incoherent resonant scattering, the Hall effect is accounted for properly by single-impurity models of skew scattering.
    EPL (Europhysics Letters) 07/2007; 1(11):579. · 2.26 Impact Factor
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    ABSTRACT: We have investigated the dimensionality and origin of the magnetotransport properties of LaAlO3 films epitaxially grown on TiO2-terminated SrTiO3(001) substrates. High-mobility conduction is observed at low deposition oxygen pressures (P(O2)<10(-5) mbar) and has a three-dimensional character. However, at higher P(O2) the conduction is dramatically suppressed and nonmetallic behavior appears. Experimental data strongly support an interpretation of these properties based on the creation of oxygen vacancies in the SrTiO3 substrates during the growth of the LaAlO3 layer. When grown on SrTiO3 substrates at low P(O2), other oxides generate the same high mobility as LaAlO3 films. This opens interesting prospects for all-oxide electronics.
    Physical Review Letters 05/2007; 98(21):216803. · 7.73 Impact Factor
  • Z. Ogorelec, A. Hamzić, M. Basletić
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    ABSTRACT: We describe an attempt to find the key parameter for the optimization of recently discovered large magnetoresistance in non-stoichiometric silver chalcogenides. Our measurements of the resistivity, magnetoresistance and the Hall effect of Ag2Se and their simple analysis lead us to the conclusion that the most important optimization variable is the Hall mobility of the charge carriers. We suggest that the largest magnetoresistance may be expected in the samples with the Hall mobility equal to about 0.1 m2/Vs.
    EPL (Europhysics Letters) 01/2007; 46(1):56. · 2.26 Impact Factor
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    ABSTRACT: Strongly underdoped RuSr 1.9 La 0.1 GdCu 2 O 8 has been comprehensively studied by dc magnetization, microwave measurements, magnetoresistivity and Hall resistivity in fields up to 9 T and temperatures down to 1.75 K. Electron doping by La reduces the hole concentration in the CuO 2 planes and completely suppresses superconductivity. Microwave absorption, dc resistivity and ordinary Hall effect data indicate that the carrier concentration is reduced and a semiconductor-like temperature dependence is observed. Two magnetic ordering transitions are observed. The ruthenium sublattice orders antiferromagnetically at 155 K in low applied magnetic fields, and the gadolinium sublattice orders antiferromagnetically at 2.8 K. The magnetoresistivity in this compound exhibits a complicated temperature dependence due to the occurence of the two magnetic orders and spin fluctuations. It is shown that the ruthenium magnetism influences the conductivity in the RuO 2 layers while the gadolinium magnetism influences the conductivity in the CuO 2 layers. The magnetoresistivity is isotropic above 4 K, but it becomes anisotropic close to the gadolinium antiferromagnetic order temperature. Copyright EDP Sciences/Società Italiana di Fisica/Springer-Verlag 2007
    Physics of Condensed Matter 01/2007; 57(1):1-7. · 1.28 Impact Factor
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    ABSTRACT: We report on the magnetotransport properties and spin polarization of Co-doped (La,Sr)TiO3 (Co-LSTO) thin films in which the host oxide is a strongly correlated metal with a high density of carriers. In order to probe the spin polarization, we have performed tunneling magnetoresistance (TMR) measurements on magnetic tunnel junctions associating Co-LSTO and Co electrodes. A large spin polarization of around −80% has been determined at low temperatures, indicating that the carriers in this system are highly spin-polarized. We also report on the planar magnetotransport experiments on Co-LSTO films grown on SrTiO3 substrates. The electrical properties of these samples are strongly dependent on the growth conditions and large electronic mobilities as high as 104cm2/Vs at T
    Journal of Magnetism and Magnetic Materials 01/2007; 310(2):2111-2113. · 1.83 Impact Factor
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    ABSTRACT: The authors present results on current induced domain wall motion in Co/Cu/CoFeB trilayered stripes. The threshold current densities are around 106 A/cm2 at zero field, i.e., about two orders of magnitude smaller than in single NiFe stripes. The domain wall motion is assisted when the field torque acts in the same direction as the spin torque. When the field torque is opposed to the spin transfer one and above a threshold field, the authors observe a reversible displacement of the domain wall (peak in the dV/dI measurements). This can be ascribed to the onset of domain wall fluctuations, which is confirmed by micromagnetic simulations.
    Applied Physics Letters 01/2007; 90. · 3.79 Impact Factor
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    ABSTRACT: LaAlO3/SrTiO3 structures showing high mobility conduction have recently aroused large expectations as they might represent a major step towards the conception of all-oxide electronics devices. For the development of these technological applications a full understanding of the dimensionality and origin of the conducting electronic system is crucial. To shed light on this issue, we have investigated the magnetotransport properties of a LaAlO3 layer epitaxially grown at low oxygen pressure on a TiO2-terminated (001)-SrTiO3 substrate. In agreement with recent reports, a low-temperature mobility of about 10^4 cm2/Vs has been found. We conclusively show that the electronic system is three-dimensional, excluding any interfacial confinement of carriers. We argue that the high-mobility conduction originates from the doping of SrTiO3 with oxygen vacancies and that it extends over hundreds of microns into the SrTiO3 substrate. Such high mobility SrTiO3-based heterostructures have a unique potential for electronic and spintronics devices.
    07/2006;
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    ABSTRACT: The study reports on the magnetic properties and spin polarization of (La,Sr)Ti<sub>1-x</sub>Co<sub>x</sub>O<sub>3</sub> (Co-LSTO) thin films. Tunneling magnetoresistance (TMR) measurements on magnetic tunnel junctions were performed to probe the spin polarisation. A large spin of -80% has been determined at low temperature, indicating that the carriers are highly spin-polarized in this system. Structural analysis was done through use of combining high-resolution transmission electron microscopy, Auger electron spectroscopy and X-ray magnetic circular dichroism. As a result, the measured ferromagnetism and high spin polarization are intrinsic properties of this DMOS. Finally a report on planar magnetotransport experiments on Co-LSTO films grown on SrTiO<sub>3</sub> (STO) substrates is presented.
    Magnetics Conference, 2006. INTERMAG 2006. IEEE International; 06/2006
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    ABSTRACT: We present the high-temperature (70 K<T<300 K) resistivity anisotropy and Hall effect measurements of the quasi-one-dimensional (1D) organic conductor (TMTTF)2AsF6. The temperature variations of the resistivity are pronouncedly different for the three different directions, with metalliclike at high temperatures for the a axis only. Above 220 K the Hall coefficient RH is constant, positive, and strongly enhanced over the expected value; and the corresponding carrier concentration is almost 100 times lower than calculated for one hole/unit cell. Our results give evidence for the existence of a high-temperature regime above 200 K where the 1D Luttinger liquid features appear in the transport properties. Our measurements also give strong evidence of charge ordering in (TMTTF)2AsF6. At the charge-ordering transition TCO≈100 K, RH(T) abruptly changes its behavior, switches sign, and rapidly increases with further temperature decrease.
    Physical Review B 03/2006; 73(11). · 3.66 Impact Factor

Publication Stats

1k Citations
140.18 Total Impact Points

Institutions

  • 1988–2011
    • University of Zagreb
      • Department of Physics (VEF)
      Zagreb, Grad Zagreb, Croatia
  • 2007
    • Thales Group
      Cannes, Provence-Alpes-Côte d'Azur, France
  • 1985–2007
    • Université Paris-Sud 11
      • Laboratoire de Physique des Solides
      Paris, Ile-de-France, France
  • 1991
    • Laboratory of Plasma Physics
      Paliseau, Île-de-France, France