Correlation between the extraordinary Hall constant and electrical resistivity minima in Co-rich metallic glasses

Journals published by the American Physical Society can be found at http://journals.aps.org/The Hall effect has been studied in some Co-rich ferromagnetic metallic glasses which show resistivity (rho) minima at low temperatures. It is found that the extraordinary Hall constant (R-s) shows a corresponding minimum. The scaling relation R(s)similar torho(n) holds with nsimilar or equal to2 showing the dominance of quantum transport in these high-resistive disordered systems. The temperature dependences of magnetization and electrical resistivity are also interpreted in terms of existing theories

Anisotropic magnetoresistance of single-crystal HoNi2B2C and the interplay of magnetic and superconducting order

Journals published by the American Physical Society can be found at http://journals.aps.org/The in-plane resistivity and magnetization measurements as a function of the magnitude and direction of the magnetic field and the temperature are reported for single-crystal samples of the HoNi2B2C magnetic superconductor. Features corresponding to several distinct magnetic phases and the coexistence of superconductivity with two of the magnetic phases are observed. Contrary to previous measurements for polycrystalline samples, reentrant superconductivity is not observed in the absence of a field for these samples. The measurements indicate an extremely rich interplay between superconductivity and different magnetic structures that can be influenced by field, temperature, and current. The results correlate quantitatively with and complement previous determinations of the magnetic phase diagram and qualitatively with determinations of the superconducting phases by measurements of the single-crystal magnetization and heat capacity. HoNi2B2C is highly anisotropic, and phase diagrams for the field along the (100) and (001) directions are presented

Transport and superconducting properties of RNi2B2C (R=Y, Lu) single crystals

Journals published by the American Physical Society can be found at http://journals.aps.org/The in-plane resistivity, in-plane absolute thermopower, and upper critical held measurements are reported for single-crystal samples of YNi2B2C and LuNi2B2C superconductors. The in-plane resistivity shows metallic behavior and varies approximately linearly with temperature near room temperature (RT) but shows nearly quadratic behavior in temperature at low temperatures. The YNi2B2C and LuNi2B2C single-crystal samples exhibit large transverse magnetoresistance (approximate to 6-8% at 45 kOe) in the ab plane. The absolute thermopower S(T) is negative from RT to the superconducting transition temperature T-c. Its magnitude at RT is a few times of the value for a typical good metal. S(T) is approximately linear in temperature between approximate to 150 K and RT. Extrapolation to T = 0 gives large intercepts (few mu V/K) for both samples suggesting the presence of a much larger ''knee'' than would be expected from electron-phonon interaction renormalization effects. The upper critical fields for H parallel and perpendicular to the c axis and the superconducting parameters derived from it do not show any anisotropy for the YNi2B2C single-crystal samples in agreement with magnetization and torque magnetometry measurements, but a small anisotropy is observed for the LuNi2B2C single crystals. The analysis shows that these are moderately strong-coupling type-II superconductors (similar to the A-15 compounds) with a value of the electron-phonon coupling parameter lambda(0) approximately equal to 1.2 for YNi2B2C and 1.0 for LuNi2B2C, the Ginzburg-Landau coherence length xi(0) approximately equal to 70 Angstrom, and H-c2(0) similar to 60-70 kOe. The temperature dependence of the upper critical field shows a positive curvature near T-c in disagreement with the Werthamer, Helfand, Hohenberg, and Maki (WHHM) theory but in agreement with a recent solution of the Gor'kov equation using a basis formed by Landau levels (Bahcall); however, the data show a severe disagreement between the observed low-temperature behavior of H-c2(T) and that predicted either by WHHM or Bahcall's expressions

Electrical resistivity and thermopower of single-crystal RNi2B2C (R=Dy, Ho, Er, Tm) magnetic superconductors

Journals published by the American Physical Society can be found at http://journals.aps.org/The in-plane resistivity rho and thermopower S of single crystal RNi2B2C (R=Dy, Ho, Er, Tm) has been measured from 4 to 300 K. The resistivity is linear in temperature from about 100 to 300 K, but the low-temperature dependence goes as T-p With p = 3.0, 2.6, 2.0, and 1.4, respectively, from Dy to Tm, in comparison to the T-2 behavior previously reported for LuNi2B2C. The thermopower exhibits a region linear in T from about 100 to 300 K where the coefficient b scales by the de Gennes factor (g-1)(2)J(J+1) for different R = Lu, Tm-Dy. The quantity S-b T is surprisingly similar in temperature dependence and magnitude for samples with R = Y, Lu, Dy-Tm, suggesting a common, nonmagnetic contribution to the thermopower of these compounds

Hall-Coefficient and Resistivity of Amorphous Ti1-Xalx Films

Journals published by the American Physical Society can be found at http://journals.aps.org/The resistivity of codeposited amorphous Ti1-xAlx films has been measured from 1.5 to 300 K over the composition range 0.4 less-than-or-equal-to x less-than-or-equal-to 0.92, and the Hall coefficient has been measured at 4 K. The resistivity exhibits a relatively small temperature dependence. The magnitude of the room-temperature resistivity varies appreciably with composition, with a broad maximum around 250 muOMEGA cm near x almost-equal-to 0.5. The Hall coefficient is positive at x = 0.4 and increases to a maximum at x almost-equal-to 0.6. It becomes negative at x almost-equal-to 0.85 with a value comparable to that of liquid Al at the highest value of x. The positive values of the Hall coefficient and their dramatic increase with x below x almost-equal-to 0. 5 are discussed in terms of current theories for a positive Hall coefficient

Anisotropic magnetoresistance of single-crystal HoNi2B2C and the interplay of magnetic and superconducting order

The in-plane resistivity and magnetization measurements as a function of the magnitude and direction of the magnetic field and the temperature are reported for single-crystal samples of the HoNi2B2C magnetic superconductor. Features corresponding to several distinct magnetic phases and the coexistence of superconductivity with two of the magnetic phases are observed. Contrary to previous measurements for polycrystalline samples, reentrant superconductivity is not observed in the absence of a field for these samples. The measurements indicate an extremely rich interplay between superconductivity and different magnetic structures that can be influenced by field, temperature, and current. The results correlate quantitatively with and complement previous determinations of the magnetic phase diagram and qualitatively with determinations of the superconducting phases by measurements of the single-crystal magnetization and heat capacity. HoNi2B2C is highly anisotropic, and phase diagrams for the field along the (100) and (001) directions are presented.This article is published as Rathnayaka, K. D. D., Donald G. Naugle, B. K. Cho, and P. C. Canfield. "Anisotropic magnetoresistance of single-crystal Ho Ni 2 B 2 C and the interplay of magnetic and superconducting order." Physical Review B 53, no. 9 (1996): 5688. DOI: 10.1103/PhysRevB.53.5688. Copyright 1996 American Physical Society. Posted with permission

Electrical resistivity and thermopower of single-crystal RNi2B2C (R=Dy, Ho, Er, Tm) magnetic superconductors

The in-plane resistivity rho and thermopower S of single crystal RNi2B2C (R=Dy, Ho, Er, Tm) has been measured from 4 to 300 K. The resistivity is linear in temperature from about 100 to 300 K, but the low-temperature dependence goes as T-p With p = 3.0, 2.6, 2.0, and 1.4, respectively, from Dy to Tm, in comparison to the T-2 behavior previously reported for LuNi2B2C. The thermopower exhibits a region linear in T from about 100 to 300 K where the coefficient b scales by the de Gennes factor (g-1)(2)J(J+1) for different R = Lu, Tm-Dy. The quantity S-b T is surprisingly similar in temperature dependence and magnitude for samples with R = Y, Lu, Dy-Tm, suggesting a common, nonmagnetic contribution to the thermopower of these compounds.This article is published as Bhatnagar, A. K., K. D. D. Rathnayaka, Donald G. Naugle, and P. C. Canfield. "Electrical resistivity and thermopower of single-crystal R Ni 2 B 2 C (R= Dy, Ho, Er, Tm) magnetic superconductors." Physical Review B 56, no. 1 (1997): 437. DOI: 10.1103/PhysRevB.56.437. Copyright 1997 American Physical Society. Posted with permission

Low-temperature magnetization in Ni-rich gamma-Ni100-x-yFexVy alloys

Journals published by the American Physical Society can be found at http://journals.aps.org/Detailed studies of the temperature dependence of the spontaneous magnetization have been made in eight different compositions of gamma-Ni100-x-yFexVy (4 less than or equal to x less than or equal to 17; 2 less than or equal to y less than or equal to 18) alloys at a magnetic field of 30 kOe between 4.2 and 50 K. The values of the Curie temperature (Tc) and the saturation magnetization (Mo) an found to decrease with the increase of V. This is understood since the addition of V (which is antiferromagnetic) suppresses the ferromagnetic order in the NiFe binary alloys. The magnetization of the alloys with low V (y less than or equal to 11 at. %) has shown a good fit to only the spin-wave T-3/2 term whereas the data for the high V (gamma greater than or equal to 12 at. %) alloys require an additional Stoner T-2 term (for weak itinerant ferromagnets). This indicates that the addition of more V gives the alloys a weak itinerant electron character. The range of temperature of the above analysis is much lower than 0.1T(C) for most of the alloys. Also, the Arrott plots near Te show a set of almost parallel isothermal lines supporting the presence of the Stoner term. Thus the present magnetization studies show convincingly a transition from the localized to the weak itinerant electron ferromagnetism in the high V (gamma greater than or equal to 12 at. %) alloys

Hall-Coefficient for Oriented Tl2ba2cacu2o8+delta Thin-Films

Journals published by the American Physical Society can be found at http://journals.aps.org/Measurements of the Hall coefficient and resistivity for highly oriented Tl2Ba2CaCu2O8+delta thin films are reported. The temperature dependence of cotTHETA(H), where THETA(H) is the normal-state Hall angle, for a single-phase (2:2:1:2) film sample and for other Tl-based phases is found to be linear in T2. This behavior is in agreement with recent predictions based on Anderson's spinon-holon model, but it is surprisingly general since it still holds for samples in which the resistivity does not follow Anderson's predicted linear behavior and in which superconductivity is partially or completely suppressed

Borocarbide Thin Films and Tunneling Measurements

The results obtained by their group in thin film fabrication and STM tunneling on superconducting borocarbides YNi{sub 2}B{sub 2}C have been be briefly reviewed. Results concerning the microwave surface impedance and the S/N planar junctions on LuNi{sub 2}B{sub 2}C thin films have been also presented and analyzed. These new data unambiguously confirm the full BCS nature of the superconducting gap in borocarbides and the absence of significant pair-breaking effects in LuNi{sub 2}B{sub 2}C