Electrical Resistivity In Magnetic Fields Research Articles

Anomalous Anisotropic Magnetoresistance And Magnetization In Mn3.69Bi95.69Fe0.62

It was found that the Mn3.69Bi95.69Fe0.62 consists of two phases, namely of a bismuth matrix and BiMn inclusions. It is shown that the samples have a crystalline texture. Independently on the applied field orientation, maximum on the temperature dependence of magnetization is detected at Tmax ≈ 85 K, which is associated with the reorientation transition of the magnetic moments of Mn for αBiMn phase. In turn, the electrical resistivity ρ(T) also demonstrates maximum at Tmax ≈58 K in a magnetic field of 800 kA/m when H⊥I. It is established that the maximum of ρ(T) increases and is shifted toward higher temperature Tmax≈94 K when field increasing up to 2400 kA/m. At the same time no clear maximum on ρ(T) is observed for H||I. It is shown that the relative magnetoresistance, Δρ/ρ0, is increased both with decreasing temperature and with increase of the magnetic field. The measured enhancement reaches Δρ/ρ0≈250% for H||I and Δρ/ρ0≈2400% for H⊥I in magnetic field of 2400 kA/m. Thus, the strong anisotropy of ρ(T) and Δρ/ρ0(T) is established both for H⊥I and H||I. Possible explanation of observed anomalous behavior of the temperature dependences of the electrical resistivity in magnetic fields has been proposed.

Anisotropy of the electric transport properties of decagonal Al–Cu–Co(Fe) quasicrystals

The method of growth from a melt solution was used to obtain iron-alloyed (0.08 at %) Al–Cu–Co single crystals with a decagonal symmetry. The temperature dependences of the electrical resistivity in magnetic fields of 0–18 T were measured using samples oriented in the periodic direction (ρp(T)) and in the quasi-periodic plane (ρq(T)). A strong anisotropy of the resistivity was observed; the ρp(T) curve is linear, whereas the ρq(T) curve is approximated well by a second-order polynomial. A strong anisotropy of the magnetoresistance was also observed; a positive magnetoresistance Δρ/ρ ~ 10–3 for the current flowing in the quasiperiodic plane; and a weak (close to zero) negative magnetoresistance for the current flowing along the periodic direction.

Novel Electronic States of Heavy Fermion Compound YbCo2Zn20

We studied the heavy fermion compound YbCo2Zn20 with an electronic specific heat coefficient γ \( \simeq \) 8000 mJ/(K2·mol) by measuring the de Haas–van Alphen (dHvA) oscillation, Hall effect, magnetic susceptibility, and magnetization at ambient pressure, as well as the electrical resistivity in magnetic fields of up to 320 kOe and at pressures of up to 5 GPa. The detected Fermi surfaces are small in volume, reflecting the small Brillouin zone based on the large cubic lattice constant a = 14.005 A. The cyclotron effective masses, which were determined from the dHvA experiment, are found to be markedly reduced in magnetic fields. In other words, the detected cyclotron masses of 2.2–8.9 m0 (m0: the rest mass of an electron) at Hav = 117 kOe are enhanced to 100–500 m0 at 0 kOe. By applying pressure, the heavy fermion state disappears at Pc \( \simeq \) 1.8 GPa and orders antiferromagnetically for P > Pc. The field-induced antiferroquadrupolar phase, which is observed only for \(H\parallel \langle 111\rangl...

Suppression of ferromagnetism of CeTiGe3by V substitution

The crystallographic structure, magnetization, specific heat, and electrical resistivity of polycrystalline CeTi${}_{1\ensuremath{-}x}$V${}_{x}$Ge${}_{3}$ ($0\ensuremath{\le}x\ensuremath{\le}0.42$ and $x$ $=$ 1) have been studied. CeTiGe${}_{3}$ has been reported as one of the rare ferromagnetic Kondo systems with a Curie temperature ${T}_{c}$ $=$ 14 K. We present a detailed study of the low-temperature properties on this compound, including magnetization, specific heat, and electrical resistivity in magnetic fields up to 5 T. Elastic neutron-scattering experiments confirm ferromagnetic and exclude ferrimagnetic order of CeTiGe${}_{3}$. Analysis of the specific heat gives evidence of a strong magnetic anisotropy in this system as evidenced by a gap. Replacing Ti by V reduces ${T}_{c}$, with ${T}_{c}\ensuremath{\rightarrow}0$ for $x\ensuremath{\approx}0.35$, suggesting a possible ferromagnetic quantum critical point.

Relation between Metamagnetic Transition and Quantum Critical Point in Heavy Fermion Compound YbIr2Zn20

We measured the electrical resistivity in magnetic field H under pressure P for a heavy fermion compound YbIr2Zn20. The quantum critical point is found to be defined as an electronic state where the metamagnetic transition field Hm becomes zero. This is realized at Pc ≊ 5.2 GPa. The most characteristic feature in the quantum critical pressure region is an anomalously large A value of the electrical resistivity p = p0 + AT2, reaching A = 380μΩ·cm/K2 at 5.0 GPa, which is, however, strongly reduced with increasing the magnetic field: A = 1.45μΩ·cm/K2 at 80 kOe. From the result of the de Haas-van Alphen experiment at ambient pressure, the corresponding cyclotron effective mass of conduction electrons at 5.0 GPa is 400 – 500 m0 (m0: rest mass of an electron).

Optimization of the superconducting transition temperature of the filled skutteruditeBaPt4Ge12by gold substitution

The dependence of the superconducting properties of BaPt4Ge12 upon substitution of platinum by gold is investigated. Full-potential electronic structure calculations suggest that the electronic density of states and the critical temperature of superconductivity Tc increases with gold content. This is confirmed by experiments. Single phase samples of BaPt4−xAuxGe12 with x 1 are synthesized. The structural properties, magnetization, specific heat, and electrical resistivity in magnetic fields are probed. As predicted, Tc increases significantly from 5.0 K x=0 to 7.0 K x=1 .

Vortex state of Pb-substituted Bi2201 studied by in-plain resistivity measurements

In order to investigate the Pb concentration dependence of the irreversibility field H irr in the Pb-substituted Bi 2Sr 2CuO 6+ δ (Bi 2.12− x Pb x Sr 1.88CuO 6+ δ ), we have measured the temperature dependence of the in-plane electrical resistivity in magnetic fields up to 15 T parallel to the c-axis. It is found that H irr increases for x ⩽ 0.27 with increasing x, while it remarkably decreases for x > 0.32. Striking feature is the enhancement of H irr around x ∼ 0.27–0.32. A possible origin of the enhancement is the two-phase microstructures consisting of modulated and modulation-free domains. In such a case, the phase boundary of the microstructures works effectively as pinning centers for vortices, in contrast to the homogeneous modulated x = 0.18 and the homogeneous modulation-free x = 0.37. Our results strongly suggest the close relation between two-phase microstructures and the enhancement of H irr.

Itinerant iron magnetism in filled skutteruditesCaFe4Sb12andYbFe4Sb12: Stable divalent state of ytterbium

A comparative study of the filled skutterudite compounds $\mathrm{Yb}{\mathrm{Fe}}_{4}{\mathrm{Sb}}_{12}$ and $\mathrm{Ca}{\mathrm{Fe}}_{4}{\mathrm{Sb}}_{12}$ is presented. Crystal structure investigations and measurements of magnetic susceptibility, specific heat and electrical resistivity in magnetic field, and x-ray absorption spectroscopy have been performed. Almost identical structural, magnetic, and electronic properties of both compounds are observed. Electronic structure calculations support this similarity. It is concluded that ytterbium in ${\mathrm{Yb}}_{1\ensuremath{-}x}{\mathrm{Fe}}_{4}{\mathrm{Sb}}_{12}$ is stable divalent and the magnetic moments in both materials are solely due to itinerant-electron paramagnetism of the $\mathrm{Fe}\ensuremath{-}\mathrm{Sb}$ polyanion. The calcium and ytterbium iron-antimony skutterudites are nearly ferromagnetic metals and their properties are mainly governed by spin fluctuations.

Superconductivity inCeCoIn5−xSnx: Veil over an Ordered State or Novel Quantum Critical Point?

Measurements of specific heat and electrical resistivity in magnetic fields up to 9 T along [001] and temperatures down to 50 mK of Sn-substituted CeCoIn5 are reported. The maximal -ln(T) divergence of the specific heat at the upper critical field Hc2 down to the lowest temperature characteristic of non-Fermi-liquid systems at the quantum critical point (QCP), the universal scaling of the Sommerfeld coefficient, and agreement of the data with spin-fluctuation theory provide strong evidence for quantum criticality at Hc2 for all x< or =0.12 in CeCoIn5-xSnx. These results indicate the "accidental" coincidence of the QCP located near Hc2 in pure CeCoIn5, in actuality, constitute a novel quantum critical point associated with unconventional superconductivity.

A newly developed high-pressure cell by using modified Bridgman anvils for precise measurements in magnetic fields at low temperatures

We have succeeded in developing a new high-pressure cell designed for measuring the absolute value of the electrical resistivity in magnetic fields at low temperatures. This pressure cell, based on a technique using modified Bridgman anvils with a Teflon capsule, can generate nearly hydrostatic pressure at least up to 6 GPa. The most important feature of this pressure cell is its compact body which can be easily combined with a dilution refrigerator in a superconducting magnet. One of its applications is for precise magneto-transport measurements under nearly hydrostatic pressure, which is demonstrated by the investigation into the pressure-induced superconducting state of the spin-ladder Sr14−xCaxCu24O41 (x=12) single crystal.

Flux pinning and critical currents in polycrystalline MgB 2

The results of accurate electrical resistivity and ac susceptibility measurements for a well-characterized, single phase MgB 2 sample are reported. The onset of electrical resistivity in magnetic fields B≤1 T is thermally activated R∼exp(− U( T, B)/ k B T) with U 0(B)=U(T=0,B)∝1/ B for B≥0.2 T. The pinning potential U 0(B=1 T) is similar to that for YBa 2Cu 3O 7 compound, but the region of flux liquid is quite narrow and the upper critical field B c2 fairly low. High-resolution ac susceptibility measurements show homogeneous superconducting behavior (no Josephson coupled grains) and yield true zero-field critical current density J c∼(1− T/ T c) n with n≈1.2. The comparison of literature results for J c with our ones shows pronounced mass density dependence of J c in bulk untextured MgB 2 samples.

TRANSPORT AND MAGNETIC PROPERTIES OF Bi BASED MULTIPHASE SUPERCONDUCTORS

A series of (Bi,Pb)SrCuCaO samples with varying volume fraction of the 2223 phase (determined by X-ray diffraction) has been prepared. Temperature dependence of the resistance, Hall effect and magnetic susceptibility has been measured. Neither susceptibility (both dc and ac) nor electrical resistivity in magnetic field reveal the presence of the low temperature (2212) phase. On the other hand the Hall voltage in the mixed state is very sensitive to the presence of different phases. Obtained results have been discussed within the frame of the effective medium approach and related to the growth mechanism of the 2223 phase.

Anisotropic magnetic phase diagram of Ce 3Pd 20Ge 6 with quadrupolar ordering

We have constructed the magnetic phase diagram of Ce 3Pd 20Ge 6 up to 4 T by measuring the specific heat and the electrical resistivity in magnetic fields applied along three principal directions, which suggests the existence of a highly anisotropic interaction between the electric quadrupolar moments and the magnetic dipolar moments.

Peak Effect in CeRu2: Role of Crystalline Defects

We measured the electrical resistivity in magnetic fields and the Hall voltage to understand the peak effect in a superconductor with the cubic structure CeRu 2 . Two samples with residual resistivity ratios of ρ RT /ρ 0 = 240 and 12 were prepared, and the experimental results in the superconducting mixed state were compared between them. The flux flow begins at a high field and the peak effect is observed in a very narrow window in the T vs. H phase diagram near the upper critical field H c2 for the sample with ρ RT /ρ 0 = 240, while it starts at a lower field and the window where the peak effect is observed becomes wider for the sample with ρ RT /ρ 0 = 12. These characteristic features are mainly related to crystalline defects in the sample.

Crystal growth and electrical resistivity in magnetic fields in single crystalline Nd2−x Ce x CuO4−δ

High quality single crystals of Nd2−x Ce x CuO4−δ (x≈0.15) were grown by the traveling solvent floating zone (TSFZ) method. A large single crystal grain of several centimeters in length and about 5 mm in diameter was obtained. After annealing in argon gas flow, the crystals exhibited bulk superconductivity below 19.1 K. The c-axis electrical resistivity in magnetic fields up to 6 T was measured. Significant broadening behavior of the resistive transition was found, when the magnetic field was applied along c-axis. The negative magnetoresistance as well as the broadening is presented.

Electronic structure parameters of Sm 1+ xBa 2− xCu 3O y solid solution of orthorhombic and tetragonal structure

Two series of Sm 1+ x Ba 2− x Cu 3O y samples were prepared, both exhibiting a change from orthorhombic to tetragonal structure. The first is a series of solid solution of increasing Sm/Ba ratio, the second is a series of exact “123” cation stoichiometry with lowering oxygen content. Several quantities, such as electrical resistivity in magnetic field up to 8T (ϱ), Hall carrier concentration ( n H) and thermopower ( S), were measured. Despite the different chemical nature of the deviation from the initial SmBa 2Cu 3O 6.85 composition in the two series, the transport properties of the normal state change in an analogous manner. No significant differences in the Hall mobility at room temperature were revealed between 90 K superconducting and non-metallic samples; however, a wide maximum was observed for both series for samples with intermediate T c values. The critical temperature ( T c) is depressed with increasing deviation from the initial composition in both series; however, for the solid solution there is no clear 60 K plateau as for the stoichiometric series. The electronic density of states ( g( E F)) was assessed from in-field T c measurements on the basis of the GLAG theory and, independently, from analysis of S and n H values at room temperature. Both methods revealed no significant differences in the behavior of the g( E F) between the solid solution and stoichiometric series. However, the g( E F) calculated by the first method decreases fast with deviation from the initial composition, whereas the results of the second method remain nearly constant over a wide range of composition factors. The value of the g( E F) obtained for the initial SmBa 2Cu 3O 6.85 sample from the jump of the specific heat at T c based on BCS theory also agrees well with the values calculated from transport measurements.

Negative charge carriers in the 90 K plateau of REBa 2Cu 3O 7−δ

Specific heat, thermopower and electrical resistivity in magnetic field were measured in the series of polycrystalline REBa 2Cu 3O 7−δ samples from the so-called 90 K plateau of T c versus δ dependence. Clear correlations between such electronic quantities as specific heat jump, Δ C p , thermopower at 300 K, S 300, and slope of the upper critical field, d H c2/d T, were observed for all the investigated samples. We proposed some possible explanation of the observed effects in terms of the simple theory of metals and Ginzburg-Landau-Abrikosov-Gorkov theory of type-II superconductors. This analysis suggests that in the REBa 2Cu 3O 7−δ superconductors with T c from the region of the 90 K plateau there exist charge carriers of negative sign, in addition to holes dominating the Hall effect. The electronic density of states of the negative charge carriers is the highest for δ ≈ 0 and substantially lower near the edge of the plateau. Its value is responsible for the changes of Δ C p , d H c2/d T and the negative component of S 300 in the region of the 90 K plateau.

Thermally activated dissipation in Y 1Ba 2Cu 3O 7−x/Y 1Ba 2(Cu 1−xNi x) 3O 7−x superconducting multilayer thin films

Heterostructures of Y 1Ba 2Cu 3O 7− x /Y 1Ba 2(Cu 1− x Ni x ) 3O 7− x superconducting thin films have been grown on (100) yttriumstabilized ZrO 2 substrates using a pulsed laser deposition technique. The thickness of the Y 1Ba 2Cu 3O 7− x layer was changed from 120 Å to 420 Å, and the thickness of the Y 1Ba 2(Cu 1− x Ni x ) 3O 7− x layer was varied from 85 Å to 480 Å, in order to investigate thermally activated dissipation behavior due to flux motion. The resistivity transitions of multilayers have been measured below T c in magnetic fields up to 5 T. The electrical resistivity in magnetic field is thermally activated and shows a broad transition about 4 ∼ 5 K for magnetic field perpendicular to the c-axis and 8 ∼ 10 K for field parallel to the c-axis. The broadening of the resistive transition observed in multilayer thin films is shown to depend on both Y 1Ba 2Cu 3O 7− x and Y 1Ba 2(Cu 1− x Ni x ) 3O 7− x layer thickness for both magnetic fields parallel and perpendicular to the c-axis. The activation energies derived from thermally activated flux flow are proportional to the Y 1Ba 2Cu 3O 7− x layer thickness up to 360 Å, but are inversely proportional to the increase of the Y 1Ba 2(Cu 1− x Ni x ) 3O 7− x layer thickness when the other layers retain the same thickness.

Electrical resistivity change in Cu and AI stabilizer materials for superconducting magnet after low-temperature neutron irradiation

The change of electrical resistivity in magnetic field has been studied at 4.2 K in both copper and aluminum irradiated by fast neutrons at 5 K, together with the isochronal annealing behaviors and the effects of the irradiation-anneal cycles (cyclic irradiation). The increasing rate of the resistivity by the irradiation in aluminum is about three times as large as that in copper in zero magnetic field. The rates in the high purity copper with R 294k R 4,2k (RRR) of 1400 and aluminum with RRR of 1500 increase remarkably with an increase in applied magnetic field to the low irradiation doses, while those in the impure copper with RRR of 280 and 300 are independent of magnetic field. The radiation-induced resistivity in copper cannot be recovered even by annealing at 300 K. and the retained resistivity decreases in the cold-worked samples. The retained resistivity is accumulated by the cyclic irradiation. The radiation-induced resistivity of aluminum is completely annihilated by the annealing at 300 K.