Upper critical fields of Nb3Ge thin film superconductors

The upper critical field H_c2(T) of the highest T_c(～23K) Nb₃Ge superconducting films has been found to be ≈370kG at 4.2K. Measurements on lower T_c films show very broad transitions reflecting nonuniformity. The H_c2(T) characteristics are consistent with other Nb₃X type II superconductors.     

Upper critical fields of superconducting superconducting rare-earth molybdenum selenides

Upper critical fields, H_c2(T), for superconducting LaMo₆Se₈, La_0.8Eu_0.2Mo₆Se₈, La_0.8Ce_0.2Mo₆Se₈ and PrMo₆Se₈ were measured. For the best material, LaMo₆Se₈, T_c = 11.3 K, (dH_c²/dT)_T=Tc=70 kG/K and and H_c² (4.2 K) = 370 kG. These selenide compounds show promise as very high field superconductors.     

Electric and magnetic properties of the synthetic metal-copper subrodanide Cu(SCN)13

The temperature dependence of the resistance and magnetic susceptibility of the copper subrodanide Cu(SCN)_{$\text{1}\text{3}$} samples were measured at the magnetic field up to 7.3 kG and the temperature range 4.2–400 K. The resistance of the pressed pellet samples linearly increases with the temperature increasing and at 100–150 K the ?(T) line slope smoothly changes. The magnetic susceptibility at zero field linearly decreases with decreasing of the temperature, showing unusual exponential field dependence, which is rather strong at the room temperature and disappears at T → 0. It was concluded that a copper subrodanide is a synthetic metal.     

Neutron scattering investigation of the tricritical point in DyPO4

Neutron scattering experiments on DyPO₄ were performed without and with external field at temperatures between 1.65 and 3.5 K in order to determine the phase diagram and critical properties. In contrast to previous results the M(H)-curve shows typical first order behaviour fot T ? 2 K and H ? 4.2. kG. The H_c(T)-curve agrees quite well with the previous results. Critical scattering was observed at 1.65 K around the (110) magnetic Gragg-peak. A structure refinement at room temperature was also done mainly in order to check for the importance of extinction.     

γ-Detected NMR of103 mRhFe

Using the method ofγ-detection, the NMR in the metastable 40 keV-state of¹⁰³Rh in Fe (thin foils with diffused¹⁰³Pd activity) was measured in external fields of 0.5 to 14 kG. We find a zero-field resonance frequency ofv ₀=(550.3±0.5) MHz and a slope ofdv/dH= ?(0.933 ±0.017) MHz/kG, yielding g=1.22 ± 0.02. The resulting value for the hyperfine field, H_hf=(590±10) kG, is inconsistent with that of an NMR measurement in the ground state of¹⁰³Rh. Possible reasons for this discrepancy are discussed.     

Quantum interference study of electron lifetimes in magnesium

The results of an experiment at 4.2 K using the magnetoresistance oscillations caused by the interferometer trajectories in magnesium are reported. The magnesium crystal used in this experiment is believed to have an impurity concentration of ～1 ppm. The quantum state lifetime of electron states traversing the interferometer was determined to be .01±.002 nsec. In addition, the values of the three magnetic breakdown parameters needed to describe the size of the spin orbit energy gaps occurring near the AHL zone plane in magnesium were found to be:H ₁=2.90±.1KG,H ₂=12.5±.5KG,H ₃=4.25±.25KG. The presence of higher harmonics was also observed in the magnetoresistance oscillations and the higher harmonics were used to allow an experimentally meaningful value ofH ₃ to be determined. It is presently believed that the sensitivity of the interferometer to quantum state lifetimes can be extended by using the higher harmonics and hence information about electron-phonon and possibly electron-electron interactions will be obtained.     

Upper critical fields of NbxGa1-x: A binary high temperature superconductor

The upper critical fields, H_C2, of several Nb_xGa_1-x alloys with values of T_c from 13.3 K to 20.2 K have been measured at temperatures from 4.2 to 20.4 K with dc and pulsed magnet fields. For the highest T_c material, H_C2(4.2 K) = 340 kG. The data are consistent with almost complete suppression of Pauli paramagnetic limiting. Comparisons with other high T_c materials, Nb₃Al and NbAlGe are presented.     

Zeitliches Abklingen und Anisotropie von p-Terphenyl- undp-Terphenyl-Anthrazen-Mischkristallen bei Beschuß mit α-Teilchen

The time dependence of scintillation intensity from single crystals ofp-terphenyl and mixed crystals ofp-terphenyl and anthracene after bombarding with α-particles was investigated at the two temperaturesT=296 °K andT=92 °K. For the crystals ofp-terphenyl the time dependence of the scintillation anisotropy was also measured. Using the formulas given byKing andVoltz the decay curves ofp-terphenyl were decomposed into two components. Good agreement between experiment and theory was found. The ratio of the prompt intensity to the delayed intensity was determined to be 1∶2 atT=296 °K and 1∶3 atT=92 °K. The diffusion constants for triplet excitons were calculated to beD _T(296 °K)≈10^?5 cm² sec^?1 andD _T(92 °K)≈ 2×10^?6 cm² sec^?1, and the triplet-triplet interaction rate constantsχ _tt(296 °K)≈ 2.5×10^?11 cm³ sec^?1 andχ _tt(92 °K)≈0.5×10^?11 cm³ sec^?1.     

Magnetoresistance of La<Subscript>0.67</Subscript>Sr<Subscript>0.33</Subscript>MnO<Subscript>3</Subscript> epitaxial films grown on a substrate with low lattice mismatch

The structure, electrical resistivity, and magnetoresistance of La_0.67Sr_0.33MnO₃ heteroepitaxial films (120-nm thick) practically unstrained by lattice mismatch with the substrate were studied. A strong maximum of negative magnetoresistance of ≈27% (for μ₀H = 4 T) was observed at T ≈360 K. While the magnetoresistance decreased monotonically in magnitude with decreasing temperature, it was still in excess of 2% at 150 K. For T < 250 K, the temperature dependence of the electrical resistivity ρ of La_0.67Sr_0.33MnO₃ films is fitted well by the relation ρ = ρ₀ + ρ ₁(H)T^2.3, where ρ₀ = 1.1×10^?4 Ω cm, ρ₁(H = 0) = 1.8×10^?9 Ω cm/K^2.3, and ρ₁(μ₀H = 4 T)/ρ₁(H = 0) ≈0.96. The temperature dependence of a parameter γ characterizing the extent to which the electrical resistivity of the ferromagnetic phase of La_0.67Sr_0.33MnO₃ films is suppressed by a magnetic field (μ ₀H = 5 T) was determined.     

Electrical resistance and magnetoresistance of amorphous alloys Gd67Co33 and Pd80Si20

In search for structural contributions to the low temperature anomaly we report high resolution resistance and magnetoresistance measurements ($\text{0.02}\text{K}\text{? T ? 20}\text{K}$) of amorphous splats of Gd₆₇Co₃₃ and Pd₈₀Si₂₀. For both alloys, the resistivity ?(H = 0, T) has a minimum at T ～ 10 K and increases with decreasing T. The ferromagnetic Gd₆₇Co₃₃ shows a strong negative field dependence of $\text{Δ?}\text{?(0)}$, saturating at H ～ 2T for T = 4.2 K but no measurable change in $\text{??}\text{?}\text{T}$ below 10 K is observed.The diamagnetic Pd₈₀Si₂₀ exhibits a positive field dependent magnetoresistance $\text{[Δ?}\text{?(0)]}\text{(}\text{H}\text{)}$ at low temperatures. Additionally, a field dependent part in $\text{??}\text{?}\text{T}$ is found which is probably due to paramagnetic impurities (～ 1 ppm Fe). However, there is also a field independent contribution in the amorphous state of Pd₈₀Si₂₀, which vanishes after crystallization. We attribute this to non-magnetic scattering induced by the disordered structure.     

Electrical transport properties of a quasi-one-dimensional Nb3Te4 single crystal

The electrical resistance of a linear chain metal Nb₃Te₄ were measured from 1.3 to 320 K. The residual resistance ratio $\text{R(300}\text{K}\text{)}\text{R(4.2}\text{K}\text{)}$ is about 3. Nb₃Te₄ shows an anomaly in the resistivity vs temperature at about 80 K, suggesting an occurrence of a charge-density-wave transition. The transverse and longitudinal magnetoresistance at 4.2 K are proportional to the magnetic field in the range of 2–58 kOe. In the superconducting region close to the transition temperature T_c, the critical magnetic field H_c2 is proportional to δT=T_c?T. The angular dependence of H_c2 fits well with the fluxoid model of the Ginzburg-Landau theory. The ratio of the critical fields parallel and perpendicular to the chain direction is 4.8.     

Electrical resistivity and magnetoresistance of nonuniformly mechanically strained films (30 nm) of the La0.67Ca0.33MnO3 manganite

The structure, electrical resistivity, and magnetoresistance of predominantly oriented La_0.67Ca_0.33MnO₃(30 nm)/LaAlO₃ films are investigated after partial relaxation of biaxial mechanical stresses. The negative magnetoresistance MR of the films reaches a maximum at T = 235–240 K. The full width at half-maximum of the peak in the curve MR(T) for a film is five to six times greater than that for a manganite layer grown on a substrate with a small lattice mismatch. For T < 150 K, the temperature dependence of the electrical resistivity ρ of the films is fitted well by the relationship ρ = ρ₀ + ρ₁ (H)T ^4.5, where ρ₀ ≡ ρ(T = 4.2 K) and ρ₁(H) is a parameter that is independent of temperature but dependent on the magnetic field H. The parameter ρ₁(H = 0) for the La_0.67Ca_0.33MnO₃(30 nm)/LaAlO₃ films is several times larger than that for thin manganite layers only weakly strained by the substrate. The electrical resistivity ρ₁ decreases almost linear as the quantity μ₀ H increases in the field range 1–5 T.     

Positive magnetoresistance due to impurity interactions in dilute AuCr alloys

The magnetoresistance of dilute AuCr alloys (2.3–322 at.ppm) has been measured in a wide region of temperature (5-3K) and of magnetic field (up to 60 kG).The “modified Kohler's rule” was used to extract the spin dependent magnetoresistance (?_M) from measured total magnetoresistance.The results has shown that, except for the most dilute specimen, ?_M includes explicitly a positive component in addition to the ordinary negative magnetoresistance proportional to log (H/T). We have attributed this positive ?_M to the effect of the interactions between the Cr impurities by taking consideration of the generalized phase shift expression of magnetoresistance proposed by Soultie.     

Neutron diffraction determination of the magnetic phases of FeCl2·2H2O

The metamagnetic behaviour of FeCl₂·2H₂O has been determined. At T = 4.2 K the reflections of the antiferromagnetic zero-field-phase dissapear, when a magnetic field of H₁ = 39 kG is applied along the direction of sublattice magnetization. There is evidence for a ferrimagnetic phase with a unit cell in which the a axis is tripled. At H₂ = 46 kG this phase vanishes, and the magnetically saturated configuration is reached. As the temperature is increased, the three phases meet at a triple point at T_T = 11.7K and H_T = 42.0 kG.     

Nuclear magnetic resonance on oriented109In(4.2h) and110In(4.9h) after recoil implantation into Fe

Radioactive¹⁰⁹In(j ^π=9/2⁺;T _1/2=4.2h) and¹¹⁰In(j ^π=7⁺;T _1/2=4.9h) were produced via the¹⁰⁹Ag (α, xn) reactions and recoil-implanted into Fe foils. With the technique of nuclear magnetic resonance on oriented nuclei the magnetic hyperfine splittings were investigated in external magnetic fieldsB ₀=0.5...4.2 kG. The zero-field splitting were measured as 268.9(2)MHz and 147.3(3)MHz for¹⁰⁹InFe and¹¹⁰InFe, respectively. With the known hyperfine fieldB _HF(InFe)=?286.6(5) kG the nuclearg-factors are deduced asg(¹⁰⁹In)=1.231(3) andg(¹¹⁰In)=0.674(2). Our result for¹⁰⁹In shows that theπ g _9/2 g-factors vary by only ～0.1% betweenA=109 and 115. For the |π _9/2 vd _5/2〉₇₊ of¹¹⁰In the additivity relation of magnetic moments is fulfilled to on accuracy of 0.3(3)%.     

Comparison of superconducting parameters of A 15- and σ-phases of Nb−Pt

The superconducting properties of A 15- and σ-phases of the system Nb−Pt were investigated. Alloys of compositions Nb₃Pt, Nb₂Pt, and Nb₆₂Pt₃₈ were prepared by arc melting and subjected to optical microscopic and x-ray analysis for structure determination. The transition temperatures were measured inductively as well as resistively. The temperature dependences of critical fields were measured up to 35 kG. The A 15-phase has aT _c value of 8.97K and a zero temperature upper critical fieldH _c2(0) of 100 kG as compared to aT _c value of 2.14K and anH _c2(0) value of 14kG for the σ-phase. A comparison with theoretical upper critical field values seems to indicate that a spin-orbit coupling mechanism is responsible for the higher value ofH _c2(0) in the case of the A 15-phase alloy. The temperature dependent resistance up to 300 K is also measured and discussed for both the phases.     

Hall effect and magnetoresistance of (SN)x films

Hall effect and electrical conductivity have been investigated between 77 K and 300 K and the magnetoresistance at 4.2 K for a number of (SN)_x films deposited at substrate temperatures between — 10 and 50°C. The small magnitude of the Hall mobility (? 1 cm² Vsec^?1 at 300 K) and its activated temperature dependence are interpreted in terms of a heterogenous model for (SN)_x films with thin depletion layers separating highly conductive islands. The hole concentration in these islands (p ≈ 10²¹ cm^?3, the microscopic mobility (μ ≈ 500 cm² Vsec^?1 at 4.2 K) and the temperatures dependence of μ are found to be close to values for (SN)_x crystals.     

High-field magnetoresistance of polycrystalline ZrZn2

We report magnetoresistance measurements of polycrystalline ZrZn₂ as a function of temperature (4.2–48K) and magnetic field up to 19 T. The results indicate the presence of both positive and negative contributions to the magnetoresistance. The latter is due to spin fluctuations. Below T_c the resistivity varies with temperature like T² over the entire field range (0–19 T). The coefficient of the T² -term decreases with increasing field and fits a $\text{H}{}^{\mathrm{<mtext>?</mtext><mtext>1</mtext><mtext>3</mtext>}}$ dependence above ～ 10 T, in accordance with theoretical predictions. Complex behaviour of the magnetoresistance is found in the paramagnetic regime above ～ 5 T.     

Paramagnetic limiting in superconducting LiTiO ternary system

Measurements of upper critical fields H_c2 vs temperature are presented for several LiTiO compounds which have a nearly constant T_c = 11.2 ± 0.3 K and widely varying values of H_c2. Stable compounds have small spin-orbit scattering and show paramagnetic limiting effects, with the highest H_c2(4.2K) = 162 kG. Several compounds with large scattering showed a decrease in H_c2 over a period of about one year.     

Hysteresis of magnetoresistance in granular La<Subscript>0.7</Subscript>Ca<Subscript>0.3</Subscript>MnO<Subscript>3</Subscript> at low temperatures

The magnetoresistance of granular La_0.7Ca_0.3MnO₃ is studied experimentally over wide ranges of temperatures and magnetic fields. The emphasis is on anomalously large hysteresis of magnetoresistance at low temperatures (T = 4.2 K). The observed ρ(H) dependence can be qualitatively explained by spin-dependent tunneling of electrons through the dielectric boundaries of conducting granules characterized by a wide spread in the magnetic-moment magnitudes.