A. Hamzic

University of Zagreb, Zagrabia, Grad Zagreb, Croatia

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Publications (104)194.22 Total impact

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    ABSTRACT: Novel forms of the low-temperature phases in the two-dimensional molecular solids with competing interactions between charges, spins and lattice, in particular those featuring anomalous dielectric relaxation, have been the focus of intense activity in recent years. Open issues concern the nature of collective charge excitations as well as their coupling to applied ac and dc electric fields. The charge response is reasonably well understood by now in the charge-ordered phase with the formation of ferroelectric-like domains below the metal-to-insulator phase transition. Conversely, the dielectric response observed in dimer Mott insulator phases with no complete evidence for charge ordering is rather intriguing. We overview our recent results of anisotropic complex conductivity (dc - MHz) in the magnetic phase of and in the spin-liquid phase of . We discuss possible explanations for the observed dynamics within current theoretical models and compare them with the well-known fingerprints of the spin density wave response to ac electric fields.
    Full-text · Article · Mar 2015 · Physica B Condensed Matter
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    ABSTRACT: We present the measurements of the magnetotransport properties of the spin liquid candidate κ-(BEDT-TTF)2Cu2(CN)3. The temperature dependencies of dc resistivity and Hall coefficient RH as well as magnetoresistance at fixed temperatures in magnetic fields up to 5 T suggest that the charge transport takes place via 2D variable range hopping among localized states.
    No preview · Article · Mar 2015 · Physica B Condensed Matter
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    ABSTRACT: We have in detail characterized the anisotropic charge response of the dimer Mott insulator $$\kappa${}\text{$-${}}(\text{BEDT-TTF}{)}_{2}{\mathrm{Cu}}_{2}(\text{CN}{)}_{3}$ by dc conductivity, Hall effect, and dielectric spectroscopy. At room temperature, the Hall coefficient is positive and close to the value expected from stoichiometry; the temperature behavior follows the dc resistivity $$\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 relaxorlike 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.
    No preview · Article · Nov 2014 · Physical Review B
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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.
    Full-text · Article · Jul 2014
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    ABSTRACT: This chapter presents scanning tunnelling microscopy (STM) and XPS results that shows how a strong preference for adsorption above Fe2+-like subsurface cations creates an adsorption template at the Fe3O4(001) surface. The chapter also demonstrates the interface effects by means of STM and spectroscopy experiments performed on a variety of thin oxide films, e.g. MgO, CaO and SiO2 in the presence of different alkali and transition metal dopants. High quality Sr3Ru2O7 (SRO) single crystals were grown using the floating zone technique. Direct oxidation of reactive metals often results in the growth of rather thick and atomically unordered oxide films. The chapter examines the case of the conducting interface between LaAlO3 (LAO) and SrTiO3 (STO) by measuring the magneto-resistance (MR) of the LAO/STO interface in different magnetic field configurations and for different gate voltages. magnetoresistance; scanning probe microscopy; thin films; transition metals
    Full-text · Conference Paper · Jun 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.
    Preview · Article · Feb 2012 · Journal of Physics Condensed Matter
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    Y Niimi · M Morota · D H Wei · C Deranlot · M Basletic · A Hamzic · A Fert · Y Otani
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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, $(2.1 \pm 0.6)$% 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.
    Full-text · Article · Mar 2011 · Physical Review Letters
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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.
    Preview · Article · Jun 2010 · Journal of Applied Physics
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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.
    No preview · Article · Apr 2010 · Physical Review B
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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.
    No preview · Article · Mar 2009 · Physica B Condensed Matter
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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.
    Full-text · Article · Jan 2009 · Applied Physics Letters
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    ABSTRACT: We present Hall-effect measurements of two-leg ladder compounds Sr(14-x)Ca(x)Cu(24)O(41) (0 <= x <= 11.5) with the aim to determine the number of carriers participating in dc transport. Distribution of holes between the ladder and chain subsystems is one of the crucial questions important for understanding the physics of these compounds. Our Hall-effect and resistivity measurements show typical semiconducting behavior for x < 11.5. However, for x=11.5, the results are completely different, and the Hall coefficient and resistivity behavior are qualitatively similar to that of high-temperature copper-oxide superconductors. We have determined the effective number of carriers at room temperature and compared it to the number of holes in the ladders obtained by other experimental techniques. We propose that going from x=0 to x=11.5 less than 1 hole per f.u. is added to the ladders and is responsible for a pronounced change in resistivity with Ca doping.
    Full-text · Article · Oct 2008 · Physical review. B, Condensed matter
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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.
    Full-text · Article · Jul 2008 · Journal of Physics Condensed Matter
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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.
    Full-text · Article · Jun 2008 · Physical review. B, Condensed matter
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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.
    No preview · Article · Jul 2007 · EPL (Europhysics Letters)
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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.
    No preview · Article · Jun 2007 · Applied Physics Letters
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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
    Full-text · Article · May 2007 · Physics of Condensed Matter
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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.
    Preview · Article · May 2007 · Physical Review Letters
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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
    No preview · Article · Mar 2007 · Journal of Magnetism and Magnetic Materials
  • 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.
    No preview · Article · Jan 2007 · EPL (Europhysics Letters)

Publication Stats

3k Citations
194.22 Total Impact Points

Institutions

  • 1983-2015
    • University of Zagreb
      • • Department of Physics (VEF)
      • • Department of Biophysics
      Zagrabia, Grad Zagreb, Croatia
  • 1972-2007
    • Université Paris-Sud 11
      • Laboratoire de Physique des Solides
      Paris, Ile-de-France, France
  • 1997
    • Université Montpellier
      Montpelhièr, Languedoc-Roussillon, France
  • 1991
    • Laboratory of Plasma Physics
      Paliseau, Île-de-France, France
  • 1978-1987
    • Institute of Physics, Zagreb
      Zagrabia, Grad Zagreb, Croatia