Resistivity Measurements In Magnetic Fields Research Articles

Finite element simulations of logging-while-drilling and extra-deep azimuthal resistivity measurements using non-fitting grids

We propose a discretization technique using non-fitting grids to simulate magnetic field-based resistivity logging measurements. Non-fitting grids are convenient because they are simpler to generate and handle than fitting grids when the geometry is complex. On the other side, fitting grids have been historically preferred because they offer additional accuracy for a fixed problem size in the general case. In this work, we analyse the use of non-fitting grids to simulate the response of logging instruments that are based on magnetic field resistivity measurements using 2.5D Maxwell’s equations. We provide various examples demonstrating that, for these applications, if the finite element matrix coefficients are properly integrated, the accuracy loss due to the use of non-fitting grids is negligible compared to the case where fitting grids are employed.

Application of SQUIDs to low temperature and high magnetic field measurements-Ultra low noise torque magnetometry.

Torque magnetometry is a key method to measure the magnetic anisotropy and quantum oscillations in metals. In order to resolve quantum oscillations in sub-millimeter sized samples, piezo-electric micro-cantilevers were introduced. In the case of strongly correlated metals with large Fermi surfaces and high cyclotron masses, magnetic torque resolving powers in excess of 104 are required at temperatures well below 1 K and magnetic fields beyond 10 T. Here, we present a new broadband read-out scheme for piezo-electric micro-cantilevers via Wheatstone-type resistance measurements in magnetic fields up to 15 T and temperatures down to 200 mK. By using a two-stage superconducting-quantum interference device as a null detector of a cold Wheatstone bridge, we were able to achieve a magnetic moment resolution of Δm = 4 × 10-15 J/T at maximal field and 700 mK, outperforming conventional magnetometers by at least one order of magnitude in this temperature and magnetic field range. Exemplary de Haas-van Alphen measurement of a newly grown delafossite, PdRhO2, was used to show the superior performance of our setup.

The Nernst effect in ferromagnet–superconductor bilayer heterostructures

We report the transport properties of the La0.67Sr0.33MnO3 (LSMO)/YBa2Cu3O7+d (YBCO) heterostructures in the vicinity of the superconducting transition. The bottom deposited manganite was an LSMO ferromagnet with a Curie temperature of 350 K, while the top deposited cuprate was a nearly optimally doped YBCO superconductor with Tc ∼ 90 K. The samples used in these studies had fixed a thickness of LSMO layer (90 nm), whereas the thickness of the YBCO layer was varied between 20 and 100 nm. Single YBCO layers with respective thicknesses were also measured for comparison. The mixed state properties of the bilayers and single layers were characterized by means of the Nernst effect and electrical resistance measurements in magnetic fields of up to B = 12.5 T. All investigated samples show a zero-resistance state below T = 60 K in a field of 12.5 T and demonstrate gradual degradation of the superconducting properties with decreasing thickness of the YBCO layer in bilayer structures.

Evolution of the Electronic State through the Reduction Annealing in Electron-Doped Pr1.3-xLa0.7CexCuO4+δ(x=0.10) Single Crystals: Antiferromagnetism, Kondo Effect, and Superconductivity

The evolution of the electronic state through the reduction annealing has been investigated in electron-doped Pr_1.3-x_La_0.7_Ce_x_CuO_4+delta_ (x=0.10) single crystals with the so-called T' structure. From the ab plane and c axis electrical resistivity measurements in magnetic fields, it has been found that, through the reduction annealing, the strongly localized state of carriers accompanied by the antiferromagnetic (AF) pseudogap in the as-grown crystal changes to a metallic state bringing about the Kondo effect without AF pseudogap and to a superconducting state. These results are able to be understood in terms of a model based on the strong electron correlation. The complete removal of excess oxygen in the T'-cuprates is expected to result in the appearance of superconductivity in a wide range of the Ce concentration including the parent compound of x=0.

The high field ordered phase and upper critical field of the filled skutterudite systemPr(Os1−xRux)4Sb12

To study the possible competition between unconventional andBardeen–Cooper–Schrieffer superconductivity in the filled skutteruditesPr(Os1−xRux)4Sb12, the evolution of superconductivity and the high field ordered phase insingle-crystal specimens has been investigated by means of electrical resistivitymeasurements in magnetic fields up to 18 T. Whereas the upper critical fieldHc2(T) curves haveconventional shapes for x<0.4, the Hc2(T) curves are nearly linear for . For all x, Hc2(0) matches the calculated value of the orbital critical field. Features in the electricalresistivity associated with the high field ordered phase, observed clearly forPrOs4Sb12, weaken withincreasing x and vanish for .

Superconducting properties of MgB2/Fe tape heavily doped with nanosized SiC

The critical current density (Jc), upper critical field (Hc2)and irreversibility field (Hirr) have been investigated for powder-in-tube processedMgB2 tapes heavily doped with nanosized SiC up tox = 0.6 inMgB2+xSiC. We added nanosized SiC powders to the powder mixture ofMgH2 plus amorphousB and carried out Jc and resistivity measurements in magnetic fields up to 30 T at 4.2 K fortapes made from these mixtures. A maximum C substitution for B of∼3 at.% was obtained for 0.3 SiC addition. The value ofHirr at 4.2 K rose with increasing amounts of SiC addition, and a highestHirr of∼25.5 T wasobtained for x = 0.2–0.4 SiC-doped tapes. At 4.2 K and 8 T, the optimum addition level for obtaining the highestJc was in the 0.1 SiC-doped sample, while at 20 T the optimum addition level shifted toa 0.4 SiC-doped material. This shift can be explained by the enhancement ofHc2 and pinning effects of nanoparticles by the SiC addition. However, the highestlevels of SiC addition resulted in large amounts of impurity phases such asMg2Si and unreacted SiC. These impurities degrade the grain connectivity ofMgB2 andreduce Jc with increasing doping levels.

Physical Properties of Li&lt;sub&gt;2&lt;/sub&gt;Pd&lt;sub&gt;3&lt;/sub&gt;B and Li&lt;sub&gt;2&lt;/sub&gt;Pt&lt;sub&gt;3&lt;/sub&gt;B Superconductors

Superconductivity in two Li-containing compounds of Li2Pd3B and Li2Pt3B was recently discovered. These materials, showing the superconducting transition at 7.2 K and 2.6 K, respectively, have the same cubic structure (P4332) composed of distorted octahedrons without mirror or inversion symmetry along any directions. This is a very interesting feature of those materials in relation to the symmetry of superconductivity. Resistivity measurements in magnetic fields gave their upper critical fields, Hc2(0) = 45 kOe and 19 kOe, respectively. Their specific heat was measured using a heat-pulse relaxation method. The Sommerfeld coefficient (γ) and Debye temperature (θD) terms of Li2Pd3B were given as γ=9.5 mJmol-1K-2 and θD=228 K . The value of C/γT at Tc was calculated to be 1.7. In the same manner, those parameters were described for Li2Pt3B as γ=9.6 mJmol-1K-2, θD=240 K, and C/γTc =0.75, respectively. Since C/γTC in the weakcoupling limit by the BCS theory is 1.43, the value of 1.7 for Li2Pd3B is slightly higher. The electronic specific heat of Li2Pd3B at a zero magnetic field follows the typical exponetial behavior discribed in the BCS theory, while that of Li2Pt3B shows quadratic behavior. This result suggests the line nodes exist in the superconducting gap of Li2Pt3B driven by the spin-orbit interaction.

Superconducting and normal state properties of heavily hole-doped diamond synthesized at high pressure

Diamonds, synthesized at high pressures and high temperatures in the presence of boron, are heavily hole–doped by incorporation of boron into the diamond lattice. These diamonds become superconducting below Tc = 2–9 K. Synthesis in the systems B–C and B4C–C at P = 9 GPa and T = 2500–2800K result in formation of polycrystalline carbonado–like material, whereas synthesis from B–C–H gives small single crystals and intergrowth plates. Dense superconducting bodies can be prepared by compacting these single crystal particles at P = 8 GPa and T = 1800 K. Specific heat and resistivity measurements in magnetic fields prove the bulk nature of superconductivity in all pressure–synthesized samples and provide a consistent set of materials parameters that favor a conventional weak–coupling electron–phonon interpretation of the superconducting mechanism at high holedoping. Schottky barrier tunneling conductance spectra, obtained with contacts fabricated at the surface of these hole–doped diamonds, indicate the appearance of superconducting gap below Tc.

STUDY ON VORTEX DYNAMICS OF Tl2Ba2CaCu2O10 THIN FILM IN TILTED MAGNETIC FIELDS

Tl 2 Ba 2 CaCu 2 O 10 ( Tl :2212) thin films were prepared on LaAlO 3 substrates with (0 0 1) direction normal to their surface, and the logR-logH characteristics were measured using the in-plane resistivity measurements in magnetic fields tilted away from c axis to the ab-plane. The H *c- H ab phase diagram was obtained by defining a resistance criterion below the vortex phase melting transition resistance. The linear dependence of H *c on H ab in most angular range shows that the crossing-lattice structure in the tilted fields exists in Tl :2212. A perpendicular line was observed in the H *c- H ab diagram at the range of θ ¡ 0.4 ° at 88K, which was attributed to the lock-in transition.

Anisotropic superconducting properties ofMgB2single crystals probed by in-plane electrical transport measurements

We report on study of the electronic anisotropy of the newly discovered MgB2 superconductor using the in-plane resistivity measurements in magnetic field applied perpendicular and parallel to Mg and B planes of MgB2 single crystals. The results show temperature dependent anisotropy of the upper critical field with anisotropy ratio increasing from 2.2 close to Tc up to about 3 below 30K. Our estimation of the in-plane and out-of-plane coherence length of about 68A and 23A and electronic mean-free path 240A and 60A respectively indicates MgB2 single crystal as approaching clean limit type-II superconductor.

Stepwise behavior of vortex-lattice melting transition in tilted magnetic fields in single crystals of Bi(2)Sr(2)CaCu(2)O(8 + delta).

The vortex-lattice melting transition in Bi(2)Sr(2)CaCu(2)O(8 + delta) single crystals was studied using in-plane resistivity measurements in magnetic fields tilted away from the c axis to the ab plane. In order to avoid the surface barrier effect which hinders the melting transition in the conventional transport measurements, we used the Corbino geometry of electric contacts. The complete H(c) - H(ab) phase diagram of the melting transition in Bi(2)Sr(2)CaCu(2)O(8 + delta) is obtained for the first time. The c-axis melting field component H(c)(melt) exhibits the novel, stepwise dependence on the in-plane magnetic fields H(ab) which is discussed on the basis of the crossing vortex-lattice structure. The peculiar resistance behavior observed near the ab plane suggests the change of phase transition character from first to second order.

Angular dependence of the activation energy in YBCO/PBCO multilayers

The activation energy in several (YBCO){sub m}/(PBCO){sub n} superconducting multilayers was deduced from resistivity measurements in magnetic fields up to 16 T, as a function of the angle between the magnetic field and the ab planes. The activation energy U{sub 0}(B, {theta}) scales with a reduced field B{sub red} = B(sin{sup 2}{theta} + cos{sup 2}{theta}/I{sup 2}){sup 1/2}, with an angle dependent anisotropy parameter {Gamma}. A crossover from U{sub 0}{proportional{underscore}to}log B{sub red}, at low B{sub red}, to U{sub 0}{proportional{underscore}to}(B{sub red}){sup {alpha}} at high B{sub red}, is also observed. The implications of these results on vortex dynamics and on the coupling between the superconducting layers will be discussed.

Evidence of defect pinning in the superconducting Bi-(Pb)-Sr-Ca-Cu-O system

Comparative studies on Bi-2212 single crystal, Bi-2212 tape and 2223 tape have carried out using ac susceptibility, magnetization and magnetoresistivity measurements. It was found that the pinning strength increases with sequence of 2212 single crystal, 2212 tape and 2223 tape. This is consistent with results of the pinning potential, Uo, determined by using resistance measurements in magnetic fields. The differences in flux pinning are attributable to the different processing conditions which result in the difference in dislocation density.

Regions of enhanced pinning in the mixed state of the superconductor Yb 3Rh 4Sn 13

We present results of magnetisation, electrical resistivity and critical current measurements in applied magnetic fields on single crystals of the superconductor, Yb 3Rh 4Sn 13. An irreversible peak is observed in the magnetisation, at high fields below H c2. Evidence for a region of enhanced pinning is obtained from resistance measurements in magnetic fields. The temperature and field region where these anomalies are observed have been mapped. The anomalous features seen in the magnetisation and resistance measurements extend to T ∼ 0.9 T c. The results presented here for Yb 3Rh 4Sn 13 resemble those obtained for CeRu 2, which is considered a candidate for the observation of the Fulde-Ferrel-Larkin-Ovchinnikov state.

Comparative studies on single crystals and superconducting Bi-(Pb)-Sr-Ca-Cu-O tapes

Comparative studies on Bi-2212 single crystal, Bi-2212 tape and 2223 tape have been carried out using AC susceptibility, magnetisation and magnetoresistivity measurements. Bi-2212 crystals have been obtained through a spiral growth mechanism using KCl as flux. Magnetisation measurements show an enhanced flux pinning in the spiral grown crystals compared with crystals grown through a layer-by-layer mechanism. The fish tail effect in M-H loop is attributable to the spirals and screw dislocations in spiral grown Bi-2212 crystals. The irreversibility line for the 2223 tape is positioned at higher temperatures than that for the 2212 tape which is in turn positioned at higher temperatures than that for the 2212 crystals. The pinning potential, U/sub o/, for 2212 tape, determined by using resistance measurements in magnetic fields, is smaller than that of Ag/Bi-2223 tapes but larger than that for 2212 single crystals. These results indicate that the defects induced by mechanical deformation or spiral growth act as pinning centers in Bi-based materials, responsible for the improvement in flux pinning.

Peak effect in hydrogenated ReCr amorphous alloys

Pinning of flux line lattice has been studied in hydrogenated amorphous superconducting Re 94Cr 6 alloys at different hydrogen contents. Resistivity measurements in magnetic field were made. A change of pinning mechanism was observed from single to collective pinning, depending on the hydrogen content. A sharp peak of the volume pinning force was observed in the vicinity of the critical magnetic field, and explained as a result of the abrupt change in the state of the vortex lattice close to the defects.

Study of the d-magnetism instability in the system around the critical concentration by means of resistivity measurements

The substitution of Gd for Tm in the pseudobinary system gives rise to the onset of long-range magnetic order in the itinerant Co sublattice above a critical concentration . The features of the Co magnetism around the critical concentration were studied by means of resistivity measurements in magnetic fields up to 10 T and pressures up to 15 kbar. An extremely large drop of the resistivity at the ordering temperature measured for is explained by a suppression of the spin-fluctuation contribution to the resistivity in the vicinity of due to the intersublattice molecular field. The analysis of the magnetoresistance revealed that the spin fluctuations above are additionally enhanced due to short-range correlations within the f - d-electron system in a limited temperature region above . The application of external pressure results in a suppression of both the spin fluctuations and the onset of the long-range order in the Co sublattice. In the Co sublattice remains paramagnetic below the Curie temperature for . The magnetic Grüneisen parameter was found to substantially increase as the critical concentration was approached.

Superconducting fluctuation effects on the magnetoconductivity in single-crystalline YBa 2Cu 3O 7−δ} and Bi 2Sr 2CaCu 2O 8+δ}

Precise resistivity measurements in magnetic fields up to 6 T have been performed on single crystalline YBa 2 Cu 3 O 7−δ and Bi 2 Sr 2 CaCu 2 O 8+δ samples. The results show that the resistivity change becomes anomalously broad over a wide temperature region around T c in both cases in a similar fashion; the broadening is most significant when the magnetic field is applied along the crystallographic c -axis, irrespective of the relative orientation between the current and the magnetic field. This behavior is discussed in the superconducting fluctuation model and associated with the extremely short coherence length in highly two dimensional nature of the electronic structure. The broadening cannot be ascribed to the traditional Lorentz force driven mechanisms such as flux flow and flux creep models.

Broadening phenomena of the resistive transition in single-crystalline YBa 2Cu 3O 7 in magnetic fields

The superconducting transition of single-crystalline YBa 2Cu 3O 7 has been studied by resistivity measurements in magnetic fields up to 8 T in various current and magnetic field configurations. The results show that for magnetic fields applied parallel to the crystallographic c-axis, the broadening is most significant compared with any other configuration, irrespective of the relative orientation of the current and the magnetic field. This fact implies that the flux motion due to the Lorentz force is not the dominant factor for the broadening, and suggests that the broadening mechanism is closely related to a more intrinsic property of the superconducting state in this compound. In addition, a clear “shoulder” at the foot of the transition that appears only for magnetic fields applied perpendicular to the current direction manifests the existence of a Lorentz-force driven mechanism. The “shoulder” can be reasonably well interpreted as a crossover effect from flux-creep to flux-flow regime. Well above the “shoulder” level, the resistivity seems to depend only on the magnetic field orientation with respect to the crystallographic axes. For this reason, the appearance of the resistivity in this latter region is attributed to “giant” superconducting fluctuations induced by a magnetic field in the disordered flux-line state.

Superconducting and magnetic properties of the oxygen-vacancy ordered ortho-II phase of Ba2YCu3O6.5

Abstract Superconducting oxygen-vacancy ordered ortho-II phase samples of Ba 2 YCu 3 O 6.5 were prepared with a new method of low temperature annealing. Electron diffraction analyses confirmed the ordered structure with a doubled cell along the a -axis of the orthorhombic triple perovskite. Contrary to previously reported results for quenched samples of the same phase, the annealed samples exhibited a metallic temperature dependence of resistivity and an almost linearly increasing magnetic susceptibility with temperature above its T c (∼53 K). Significance of this temperature dependence of susceptibility without Curie-Weiss contribution is discussed in comparison with the recently proposed model for the La 2- x (Sr, Ba) x CuO 4 system. Resistivity measurements in magnetic fields up to 8 T revealed an anomaly around 35 K, implying existence of another superconducting phase. From low temperature specific heat measurements we found 4.0 mJ/mol-K 2 for the residual γ value in the superconducting state which is about the same found for good quality ortho-I samples.