V. N. Narozhnyi

Russian Academy of Sciences, Moskva, Moscow, Russia

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Publications (59)75.56 Total impact

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    V. N. Narozhnyi, V. N. Krasnorussky
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    ABSTRACT: The magnetic properties of CoSi single crystals have been measured in a range of temperatures T = 5.5–450 K and magnetic field strengths H ≤ 11 kOe. A comparison of the results for crystals grown in various laboratories allowed the temperature dependence of magnetic susceptibility χ(T) = M(T)/H to be determined for a hypothetical “ideal” (free of magnetic impurities and defects) CoSi crystal. The susceptibility of this ideal crystal in the entire temperature range exhibits a diamagnetic character. The χ(T) value significantly increases in absolute value with decreasing temperature and exhibits saturation at the lowest temperatures studied. For real CoSi crystals of four types, paramagnetic contributions to the susceptibility have been evaluated and nonlinear (with respect to the field) contributions to the magnetization have been separated and taken into account in the calculations of χ(T).
    Journal of Experimental and Theoretical Physics 01/2013; 116(5). · 0.92 Impact Factor
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    V. N. Narozhnyi, V. N. Krasnorussky
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    ABSTRACT: Magnetization curves of MnSi single crystals have been measured in a range of temperatures T = 5.5–35 K and magnetic field strengths H ≤ 11 kOe for H ∥ [1 1 1], [0 0 1], and [1 1 0]. Special attention has been paid to the temperature interval near T N = 28.8 K, where MnSi exhibits a transition to the state with a long-period helical magnetic structure. Some new features in the magnetic behavior of MnSi have been found. In particular, in an intermediate temperature region above the transition (28.8 K = T N ≤ T < 31.5 K), the dM(H)/dH curves exhibit anomalies that are not characteristic of the typical paramagnetic state. It is established that the line of the characteristic field H*(T) of this anomaly is a natural extrapolation of the temperature dependence of the field of the transition from a conical phase to an induced ferromagnetic phase observed at T < T N. It is concluded that the properties of MnSi in the indicated intermediate region are related to and governed by those of the conical phase (rather than of the A phase). Based on these data, magnetic phase diagrams of MnSi for H ∥ [1 1 1], [0 0 1], and [1 1 0] are plotted and compared to diagrams obtained earlier by other methods.
    Journal of Experimental and Theoretical Physics 01/2013; 116(5). · 0.92 Impact Factor
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    V. N. Narozhnyi
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    ABSTRACT: In this Comment it is argued that Stishov et al. [Phys. Rev. B 86, 064433 (2012)] incorrectly estimated concentrations of (supposed) paramagnetic centers with \mu_eff = 4.8\mu_B in the investigated CoSi crystals. Correct estimation gives concentrations of such centers from 25 to 50 times smaller than reported (appr. 0.04 to 0.16% instead of appr. 2 to 4%). Also the reported data on temperature dependence of resistivity \rho(T) of four CoSi crystals prepared in different Labs are so close to each other at T = 250 to 300K that it is extremely unlikely to be reproducible for any reasonable accuracy of resistivity measurements. These and some other problems of the paper are related to the key points of the authors argumentation. As a result their main conclusions become unjustified.
    Physical review. B, Condensed matter 10/2012; 87(13). · 3.77 Impact Factor
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    ABSTRACT: In PrBa2Cu3O7-y (Pr123) single crystals grown by the flux method the kink in the magnetic susceptibility χab(T), connected with antiferromagnetic ordering of Pr, disappears after field cooling (FC) in a field H‖ab-plane whereas the kink in χc(T) remains unchanged after FC in H‖c-axis. This seems to be connected with the coupling between the Pr and Cu(2) sublattices. The Curie constant C determined from the data reported for superconducting Pr123 crystals grown by the traveling-solvent floating zone (TSFZ), method (Zou et al, Phys. Rev. Lett., 80, 1074 (1998)) is about one half of that for our flux-grown non-superconducting crystals. Thus, we propose that concentration of Pr in TSFZ crystals seems to be about one half of the nominal concentration for Pr123. Therefore, we propose that superconductivity in TSFZ samples is connected most probably with the partial substitution of Pr by nonmagnetic Ba.
    International Journal of Modern Physics B 01/2012; 13(29n31). · 0.46 Impact Factor
  • ChemInform 01/2010; 32(38).
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    ABSTRACT: The title compound is investigated by specific heat measurements in the normal and superconducting states supplemented by upper critical field transport, susceptibility, and magnetization measurements. From a detailed analysis including also full potential electronic structure calculations for the Fermi surface sheets, Fermi velocities, and partial densities of states the presence of both strong electron-phonon interactions and considerable pair breaking has been revealed. The specific heat and the upper critical field data can be described to a first approximation by an effective single-band model close to the clean limit derived from a strongly coupled predominant hole subsystem with small Fermi velocities. However, in order to account also for Hall-conductivity and thermopower data in the literature, an effective general two-band model is proposed. This two-band model provides a flexible enough frame to describe consistently all available data within a scenario of phonon mediated s -wave superconductivity somewhat suppressed by a sizable electron-paramagnon or electron-electron Coulomb interaction. For quantitative details the relevance of soft phonons and of a Van Hove-type singularity in the electronic density of states near the Fermi energy is suggested.
    Physical Review B 01/2004; 70(17). · 3.66 Impact Factor
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    ABSTRACT: A combined experimental and theoretical study of superconducting, electronic and thermodynamic properties of various isomorphic diborides is reported. The H c2(T) data of bulk MgB2 are analyzed within a two-band model with different couplings and Fermi velocities. No bulk superconductivity was found in TaB2 and ZrB2 single crystals at temperatures T>1.5 K. Its absence is ascribed to weak electron-phonon coupling strenghth with 0.1 derived both from the comparison of the calculated density of states at the Fermi level and specific heat data as well as from the weak deformation potential.
    Journal of Low Temperature Physics 05/2003; 131(5):1159-1163. · 1.18 Impact Factor
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    ABSTRACT: Magnetic properties of high-quality Al-free nonsuperconducting GdBa2Cu3O6+y single crystals grown by flux method have been studied. The magnetic anisotropy below the Néel temperature corresponds to the direction of Gd3+ magnetic moments along the tetragonal c-axis. At T<TN clear indications of spin–flop transitions for H∥c have been observed on magnetization curves at . Magnetic phase diagrams have been obtained for H∥c as well as for H⊥c. A pronounced anisotropy in the magnetic susceptibility (unexpected for Gd-based compounds) has been found above TN.
    Physica B Condensed Matter 05/2003; s 329–333:537–538. · 1.28 Impact Factor
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    ABSTRACT: Magnetic properties of high-quality Al-free nonsuperconducting GdBa2Cu3O6+y single crystals grown by flux method have been studied. The magnetic anisotropy below the Néel temperature TN≈2.3K corresponds to the direction of Gd3+ magnetic moments along the tetragonal c-axis. At T
    Physica B Condensed Matter 01/2003; 329:537-538. · 1.28 Impact Factor
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    ABSTRACT: The discovery of a ferromagnetic form of carbon (Nature 413 (2001) 716) gives a new perspective in the investigation of magnetic materials. The existence of a ferromagnetic state with the very high Curie temperature TC≈500K for a material with only s- and p-electrons as well as the nature of its underlying interaction are of great fundamental interest. Here we report on the observation of the ferromagnetically ordered state in a material obtained by high-pressure high-temperature treatment of the fullerene C60. It has a saturation magnetization more than four times larger than that reported previously. From our data we estimated the considerably higher value of TC≈820K.
    Physica B Condensed Matter 01/2003; 329:1217-1218. · 1.28 Impact Factor
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    ABSTRACT: We report on the results of a comparative investigation of highly dense bulk MgB2 samples prepared by three methods: (i) hot deformation; (ii) high pressure sintering; and (iii) mechanical alloying of Mg and B powders with subsequent hot compaction. All types of samples were studied by AC susceptibility, DC magnetization, and resistivity measurements in magnetic fields up to yHc2a,b /Hc2c ~ 1.2\psi {\rm H}_{c2}^{\alpha ,b} /H_{c2}^c \sim 1.2 connected with some texture of MgB2 grains was found for the hot deformed samples. The samples prepared by high pressure sintering as well as by mechanical alloying show improved superconducting properties, including high upper critical fields H c2 (0 H c2 (0) 23 T), irreversibility fields H irr which are strongly shifted towards higher values H irr(T) 0.8 H c2(T) and high critical current J c (J c = 105 A/cm2 at 20 K and 1 T).
    Journal of Superconductivity 11/2002; 15(6):599-601.
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    ABSTRACT: Polycrystalline samples of the recently discovered MgCNi3 superconductor were investigated by transport, ac susceptibility, dc magnetization and specific heat measurements in magnetic fields up to 16 T. Consistent results were obtained for the temperature dependence of the upper critical field H_c2(T) from resistance, ac susceptibility and specific heat measurements. A WHH like temperature dependence of H_c2(T) and the quadratic relationship H_c2(0) ~ T_c^2 point to an effective predominant single band behavior near the quasi clean limit. Evidence for strong electron-phonon and electron-paramagnon coupling was found analyzing the specific heat data. The corresponding s- and p-wave scenarios are briefly discussed using calculated densities of states of different Fermi surface sheets.
    09/2002;
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    ABSTRACT: Magnetic properties of high-quality Al-free nonsuperconducting GdBa_2Cu_3O_{6+y} single crystals grown by flux method have been studied. The magnetic anisotropy below the N\'eel temperature T_N~2.3K corresponds to the direction of Gd^{3+} magnetic moments along the tetragonal c-axis. At T < T_N clear indications of spin-flop transitions for H||c have been observed on magnetization curves at H_{sf}~10kOe. Magnetic phase diagrams have been obtained for H||c as well as for H||ab. A pronounced anisotropy in the magnetic susceptibility (unexpected for Gd-based compounds) has been found above T_N. Comment: 2 pages, 3 figures; LT23 (Aug. 2002; Hiroshima), accepted to Physica B
    09/2002;
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    ABSTRACT: We report on the results of a comparative investigation of highly dense bulk MgB$_2$ samples prepared by three methods: (i) hot deformation; (ii) high pressure sintering; and (iii) mechanical alloying of Mg and B powders with subsequent hot compaction. All types of samples were studied by ac-susceptibility, dc-magnetization and resistivity measurements in magnetic fields up to $\mu_0H=160$ kOe. A small but distinct anisotropy of the upper critical field $H_{c2}^{a,b}/H_{c2}^{c}\sim1.2$ connected with some texture of MgB$_2$ grains was found for the hot deformed samples. The samples prepared by high pressure sintering as well as by mechanical alloying show improved superconducting properties, including high upper critical fields $H_{c2}$ ($\mu_0H_{c2}(0)\sim23$ T), irreversibility fields $H_{irr}$ which are strongly shifted towards higher values $H_{irr}(T)\sim0.8H_{c2}(T)$ and high critical current $J_c$ ($J_c=10^5$ A/cm$^2$ at 20 K and 1 T).
    07/2002;
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    ABSTRACT: Bulk textured MgB2 material of nearly full density was obtained by hot deformation of a stoichiometric MgB2 pellet prepared by a gas–solid reaction. The texture of the material was verified by comparing the X-ray diffraction patterns of the hot deformed material with isotropic MgB2 powder. A small, but distinct anisotropy of the upper critical field Ha,bc2/Hcc2∼1.2 was found by resistance and susceptibility measurements.
    Physica C Superconductivity 01/2002; · 0.72 Impact Factor
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    ABSTRACT: The upper critical field Hc2(T) of sintered pellets of MgB2 superconductor was investigated by transport, AC susceptibility and DC magnetization measurements in magnetic fields up to 16 T. The highest Hc2 values obtained from magnetization and resistance measurements (Hc2mag≈Hc290) can be attributed to the grains oriented with their ab-planes parallel to the applied field. Hc2(T) shows a positive curvature near Tc similar to that found for the borocarbides YNi2B2C and LuNi2B2C indicating that MgB2 is in the clean limit. The irreversibility field consistently determined from DC magnetization and from the imaginary component of AC susceptibility was found to increase up to 8.5 T at 10 K.
    Physica C Superconductivity 01/2002; 372:1251-1253. · 0.72 Impact Factor
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    Karl-Hartmut Müller, Vladimir N. Narozhnyi
    Physikalische Blätter. 12/2001; 57(12).
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    ABSTRACT: Electrical resistivity, magnetoresistance and magnetic susceptibility have been studied for Y1-xPrxNi2B2C samples with /0<=x<=1.0. The increase of Pr concentration x results in a rapid suppression of superconductivity, |dTc/dx|=35 K. No indication on superconductivity was observed for PrNi2B2C down to /T=0.35 K. The absence of superconductivity for PrNi2B2C and the large superconductivity suppression rate |dTc/dx| for Y1-xPrxNi2B2C correlate with the anomalously high Néel temperature of PrNi2B2C (TN~4 K). Possible reasons for the absence of superconductivity in PrNi2B2C and the large |dTc/dx| value for Y1-xPrxNi2B2C are discussed.
    Physica C Superconductivity 11/2001; · 0.72 Impact Factor
  • K-H Müller, V N Narozhnyi
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    ABSTRACT: The interaction of rare-earth magnetism and superconductivity has been a topic of interest for many years. In classical magnetic superconductors (Chevrel phases, ternary rhodium borides, etc) as well as in the high-Tc cuprates the superconducting state usually coexists with antiferromagnetic order on the rare-earth sublattice. In these compounds the magnetic ordering temperature TN is much below the superconducting transition temperature Tc. The discovery of superconducting borocarbides RT2B2C with R = Sc, Y, La, Th, Dy, Ho, Er, Tm or Lu and T = Ni, Ru, Pd or Pt (where not all of these combinations of R and T result in superconductivity) has reanimated the research on the coexistence of superconductivity and magnetic order. Most of these borocarbides crystallize in the tetragonal LuNi2B2C type structure which is an interstitial modification of the ThCr2Si2 type. Contrary to the behaviour of Cu in the cuprates Ni does not carry a magnetic moment in the borocarbides. Various types of antiferromagnetic structures on the rare-earth sublattice have been found to coexist with superconductivity in RNi2B2C for R = Tm, Er, Ho and Dy. Particularly of interest is the case of HoNi2B2C for which three different types of antiferromagnetic structures have been observed: (i) a commensurate one with Ho moments aligned ferromagnetically within layers perpendicular to the tetragonal c axis where consecutive layers are aligned in opposite directions, (ii) an incommensurate spiral along the c axis and (iii) an incommensurate a-axis-modulated structure with a modulation vector τ≈(0.55,0,0). This wave vector emerges in various RNi2B2C compounds with magnetic as well as nonmagnetic R elements and is connected with Fermi surface nesting. Both incommensurate magnetization structures have been shown to be related to the near-reentrant behaviour observed in HoNi2B2C whereas the commensurate structure coexists well with the superconducting state in this compound. The variation of TN and Tc with the de Gennes factor can roughly be drawn on straight lines from Lu to Gd and from Lu to Tb, respectively, with the exception of Yb. Consequently, Tc>TN holds for Tm, Er, Ho and Tc<TN for Dy. However, the study of various pseudoquaternary (R,R')Ni2B2C compounds has shown that this so-called de Gennes scaling is not universal for the borocarbides and it breaks down in some cases, which is attributed to effects of details of the electron structure, crystalline electric fields, the difference in the R and R' ionic radii or to the effect of nonmagnetic impurities in an antiferromagnetic superconductor. In an external magnetic field some of the RNi2B2C compounds show metamagnetic transitions combined with a large negative magnetoresistance. A small net magnetization found at low temperatures and zero magnetic field in TbNi2B2C has been interpreted as weak ferromagnetism of Dzyaloshinsky-Moriya type. A similar phenomenon observed for superconducting ErNi2B2C is still under discussion.
    Reports on Progress in Physics 07/2001; 64(8):943. · 13.23 Impact Factor
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    ABSTRACT: The upper critical field Hc2(T) of sintered pellets of the recently discovered MgB_2 superconductor was investigated by transport, ac susceptibility and dc magnetization measurements in magnetic fields up to 16 T covering a temperature range between Tc ~ 39 K and T = 3 K ~ 0.1Tc. The temperature dependence of the upper critical field, Hc2(T), shows a positive curvature near Tc similar to that found for the borocarbides YNi_2B_2C and LuNi_2B_2C indicating that MgB_2 is in the clean limit. The irreversibility line was consistently determined from dc magnetization measurements and from the imaginary component of ac susceptibility. The irreversibility field was found to increase up to 8.5 T at 10 K. Comment: 8 pages with 5 figures, submitted to Solid State Communications
    Solid State Communications 04/2001; · 1.53 Impact Factor