Pressure Dependence Of Electrical Resistivity Research Articles

Suppression of metal-insulator transition at high pressure and pressure-induced magnetic ordering in pyrochlore oxide Nd2Ir2O7

We report the pressure dependence of electrical resistance $R$($T$) of a frustrated pyrochlore oxide Nd${}_{2}$Ir${}_{2}$O${}_{7}$, which shows a second-order metal-insulator transition (MIT) at 36 K. This MIT is monotonically suppressed by the application of pressure. The insulating phase disappears at around 10 GPa. Then, in the pressure-induced metallic state above 10 GPa, a new pressure-induced phase transition emerges at around 3 K, which is characterized by a resistance drop. The new phase transition is due to a ferromagnetic (FM) ordering, which is suggested to be an ordered spin ice (two-in two-out) state of the Nd moment via the RKKY interaction. We succeeded in observing the phase competition between the MIT and the FM ordering by the application of high pressure.

Magnetic transitions in a heavy-fermion antiferromagnetU2Zn17 at high pressure

Pressure-dependent electrical resistivity and ac-calorimetrymeasurements on single crystals of the heavy-fermion antiferromagnetU2Zn17 at pressures to 5.5 GPa reveal that the low temperature magnetic order changes above ∼ 3 GPa. The Neéltemperature (TN = 9.7 K at ambient pressure) decreases slowly for pressures below3 GPa, but above this pressure a new magnetic state develops atTM≈8.7 K. This magnetic phase becomes more stable with pressure increase (dTM/dP = 1 K GPa − 1,TM = 10.5 K at 5.3 GPa). Theheavy-electron state in U2Zn17 is robust against pressure—the electronic specific heat coefficientγ≈0.4 J mol − 1 K − 2 is nearly pressure independent for both magnetic phases. Magnetic ac-susceptibilitymeasurements show that the pressure-induced state is not ferromagnetic.

Electronic Structure and Electrical Resistivity of α-Boron under High Pressure

Recently, it has been discovered that the semiconductor α-boron becomes metallic at high pressures and finally undergoes a superconducting transition at 160 GPa, without causing any phase transition. Before the superconducting transition, a step is often observed in the pressure dependence of electrical resistivity in this class of boron crystals, which possess icosahedron-based structures. This step structure used to be thought to occur due to a phase transitions. In the present paper, we show that the step of α-boron at 50 GPa is not due to a phase transition. It is caused by a gradual change in the bonding character from semiconductor to metal. The increase in the metallic character is caused by the shortening of the three-center bond, which is a characteristic feature of icosahedron-based boron crystals. This shortening of the three-center bond enhances the bonding character of the conduction bottom band and finally closes the band gap. However, even far before the gap closing, the shortening has important consequences for the crystal properties of α-boron: for the changes in the deformation of the lattice and in the librational phonon mode at approximately 50 GPa. This change in structure affects the change in band structure, that is, the bottom of the conduction band initially moves from the Γ point toward the Z point until p =50 GPa and then almost terminates in the middle point. The step in resistivity is a direct consequence of the change in this energy gap. This provides a coherent understanding of the characteristic changes in resistivity, the deformation of the lattice, and the librational mode.

High-pressure cell for a SQUID magnetometer with a plug for in situ pressure measurements

We describe the design of a miniature high-pressure cell built for a Magnetic Property Measurement System based on the Superconducting Quantum Interference Device technology magnetometer. The key feature of the cell is the plug for in situ pressure measurements with feed-through wires connected to a manganin pressure sensor, which has a known pressure dependence of electrical resistivity. By monitoring pressure continuously during magnetisation measurements in the range of operational temperatures the true pressure can always be established.

A theoretical study of band-gap and electrical resistivity of FeS2 (pyrite) at high pressure

The pressure dependence of electrical resistivity of FeS2 (pyrite) has been studied with the help of a simple analytical relation. The calculated results are found in reasonable agreement with the experimental measurements. The computed results are then utilized for the evaluation of pressure dependence of band-gap of FeS2 (pyrite). The obtained results are found to be close to the experimental data. We have also estimated the expected pressure 109.50 GPa for metallization of FeS2 (pyrite), which compares well with the estimated pressure 80(±8) GPa predicted through experiment. The pressure coefficient of logarithm of resistivity and band-gap energy has also been evaluated. Our results are near to the values obtained through the experiment.

Superconductivity of NdFeAsO1-yunder Hydrostatic Pressure

We briefly report pressure dependence of electrical resistivity in fluorine-free, oxygen- deficient, NdFeAsO 1- y (1- y = 0.85, 0.8, and 0.6, nominal compositions) under hydrostatic high pressure up to 18 GPa. Superconducting temperatures, T C decrease in every composition by applying pressure. In NdFeAsO 0.85 , which shows no superconductivity at ambient pressure, steep drop of resistivity appears at around 20 K above 5 GPa as resistivity anomaly at around 150 K is suppressed by applying pressure.

Investigation of [formula omitted] at pressures to 9.5 GPa

We have performed pressure-dependent electrical resistivity measurements of a single crystal Ce 2 Pd 3 Si 5 , which is an antiferromagnetic Kondo lattice compound, at pressures up to 9.5 GPa and at temperatures down to ∼ 0.4 K . As the pressure is increased, the Néel temperature T N deduced from the temperature dependence of resistivity decreases steeply above 4.8 GPa and disappears at P ⩾ 8.6 GPa . Both A and ρ 0 values in Fermi liquid law ρ = ρ 0 + AT 2 at low temperature region increase abruptly above 4.8 GPa and exhibit a plateau at ∼ 9 GPa . These results suggest that non-magnetic state could be formed at P ⩾ 8.6 GPa and that possible quantum critical point might exist at pressures around 9 GPa in this compound. However, there is no sign of superconductivity in resistivity data at the lowest temperature we studied around the possible QCP.

De Haas-van Alphen effect in [formula omitted] under pressure

We report the pressure dependence of electrical resistivity and de Haas-van Alphen effect in an antiferromagnet CeTl 3 . With increasing pressure the Néel temperature T N decreases monotonically and both ρ 0 and A values of the resistivity ρ = ρ 0 + AT 2 in the Fermi liquid relation increase, reflecting the approach to the quantum critical point. The critical pressure P c is estimated to be about 6 GPa. The cyclotron effective masses also increase with increasing pressure.

Pressure–temperature–composition phase diagram of [formula omitted][formula omitted

In this work a preliminary pressure–temperature–composition phase diagram for the Ce 2 Rh ( 1 - x ) Ir x In 8 heavy-fermions (HF) materials is reported, built from pressure-dependent electrical resistivity ( ρ ( T ) ) measurements on single-crystalline samples. Although neither of the two end members is an ambient-pressure SC, a transition to a zero-resistance (ZR) state was found at ambient pressure ( T C ≈ 600 mK ) in a narrow Ir concentration range (around x = 0.5 ). Pressures not higher than 10 kbar are sufficient to suppress this ZR state for all measured concentrations, in contrast to the 115 materials.

High pressure electrical resistivity behaviour on nano-crystalline vacancy doped perovskite manganites

We report here for the first time, the pressure dependence of the electrical resistivity of vacancy-doped nano-crystalline manganites up to 2 GPa at room temperature. The nano-crystalline samples with vacancy doping at La- and Mn-sites, respectively, were synthesized by sol–gel technique and particle size was determined by width in the X-ray diffraction peaks. The pressure dependent electrical resistivity measurements on La-deficient system (La 0.9Mn 0.8Fe 0.2O Δ ) and Mn-deficient system (La 0.86Sr 0.14Mn 0.80Fe 0.16O Δ ) show a similar trend by having a sudden change in the resistivity at 0.3 GPa. Further increase in pressure reduces the resistivity monotonically for La-deficient system up to 1.6 GPa while Mn-deficient system undergoes another sudden change in the resistivity at 0.78 GPa. The behaviour of the vacancy-doped systems were compared with stoichiometric system (La 0.8Sr 0.2Mn 0.8Fe 0.2O 3) which showed a similar phase transition at 0.52 GPa. The cross over of localized-electron to band magnetism could be seen clearly through low temperature Mössbauer measurements.

Optical and electrical properties of ZrSe3 single crystals grown by chemical vapour transport technique

Single crystals of the lamellar compound, ZrSe3, were grown by chemical vapour transport technique using iodine as a transporting agent. The grown crystals were characterized with the help of energy dispersive analysis by X-ray (EDAX), which gave confirmation about the stoichiometry. The optical band gap measurement of as grown crystals was carried out with the help of optical absorption spectra in the range 700–1450 nm. The indirect as well as direct band gap of ZrSe3 were found to be 1.1 eV and 1.47 eV, respectively. The resistivity of the as grown crystals was measured using van der Pauw method. The Hall parameters of the grown crystals were determined at room temperature from Hall effect measurements. Electrical resistivity measurements were performed on this crystal in the temperature range 303–423 K. The crystals were found to exhibit semiconducting nature in this range. The activation energy and anisotropy measurements were carried out for this crystal. Pressure dependence of electrical resistance was studied using Bridgman opposed anvils set up up to 8 GPa. The semiconducting nature of ZrSe3 single crystal was inferred from the graph of resistance vs pressure. The results obtained are discussed in detail.

Electronic transport and structural properties of electronically correlated CuV2S4

Abstract Electronic transport measurements and structural investigations were performed on the electronically correlated metal CuV2S4, which displays phase transitions at T=55 and 90 K . Apparently, a small degree of disorder in the material suppresses the phase transitions and has a distinct effect on the temperature dependent Hall constant. Pressure dependent electrical resistivity measurements were performed to study the evolution of the phase transitions as a function of pressure.

Pressure-dependent electrical resistivity of the filled skutterudite compound CeRu4Sb12

Abstract The electrical resistivity of the filled skutterudite compound CeRu4Sb12 was measured in the temperature range 2– 300 K and under hydrostatic pressures up to 8 GPa . Above 6 GPa , we observed metal-semiconductor transition in CeRu4Sb12 at low temperature and a energy gap estimated from activation law was enhanced with increasing pressure at a rate of 12.2 K / GPa . Semiconductive behavior of CeRu4Sb12 under high pressure may have the same origin as other Ce-based skutterudite compounds which show semiconducting behavior.

Pressure dependence of quadrupole ordering temperature TQ in CeB 6

Pressure dependence of electrical resistance in CeB 6 is investigated up to 13 GPa. A maximum in temperature dependence of the resistance shifts to higher temperature by the application of pressure. The quadrupole ordering temperature T Q shows no obvious pressure dependence at zero field, while the field dependence of T Q is enhanced slightly under high pressure.

Effect of pressure on the ferroquadrupolar compound TmAu 2

TmAu 2 with a simple body-centered tetragonal MoSi 2-type structure undergoes an electric transition to a ferroquadrupolar ordered state at T Q of 7.0 K and a magnetic transition to an antiferomagnetic state at T N of 3.2 K. We have measured pressure dependence of electrical resistivity on single-crystalline TmAu 2 sample. The results reveal that the T N decreased with increasing pressure (∂ T N/∂ P=−4.54 mK/kbar), while the T Q increased with increasing pressure (∂ T Q/∂ P=21.5 mK/kbar).

Melting boundary of Fe‐17%Si up to 5.5 GPa and the timing of core formation

Melting of Fe‐17wt%Si has been investigated at temperatures up to 1600°C and pressures up to 5.5 GPa in a cubic anvil press. The melting temperature, TM, was identified with the discontinuity in temperature and pressure dependence of electrical resistance. Two types of electrode materials, Pt and Fe, were used and gave consistent melting results. TM increases with pressure from 1200°C at 1 atm to 1430°C at 5.5 GPa. dTM/dP decreases with pressure and reaches a value of zero at P∼5 GPa. Combined with the thermal profiles of the proto‐Earth, the pressure independence of the melting boundary of Fe‐17%Si at the highest pressures of this study suggests core formation began early in Earth accretion with a substantial liquid metal phase fraction between 30 Ma and 42 Ma.

Erratum: Pressure-dependent electrical resistivity ofRCo2compounds (R=rare earth) [Phys. Rev. B57, 2904 (1998)

Erratum: Pressure-dependent electrical resistivity of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>R</mml:mi><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">Co</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>compounds (<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>R</mml:mi></mml:math>=rare earth) [Phys. Rev. B<b>57</b>, 2904 (1998)

Itinerant f-electron antiferromagnetism in UGa 3

Single crystals of the antiferromagnetic compound UGa 3 were studied by means of pressure dependent electrical resistivity measurements. The Néel temperature was found to decrease with rising pressure at the rate of −1.4 K/bar. A rapid reduction of T N was also observed in the electrical resistivity studies of the pseudobinary system U(Ga 1− x Ge x ) 3, where the substitution for Ga of a smaller atom was equivalent to a positive chemical pressure. The results corroborate an itinerant- electron nature of the magnetism in UGa 3 which was suggested before on the basis of the peculiar magnetic and thermodynamic properties of this compound.

Specific heat and electrical resistivity studies on Ce 2T 2In, T = Ni, Rh, Pt, Pd, Cu and Au

Specific heat measurements under external magnetic fields and pressure-dependent electrical resistivity measurements were performed on the new ternary compounds Ce 2T 2In. While the compounds with T = Pd, Cu and Au are magnetically ordered Kondo lattices, those with T = Ni and Rh are intermediate valence compounds. Ce 2Pt 2In was found to be a nonmagnetic heavy fermion system with a pronounced pressure dependence of the Kondo interaction.

Semiconducting behaviour and pressure dependence of electrical resistivity in tin monoselenide single crystals grown by a modified direct vapour transport technique

Tin monoselenide single crystals were grown successfully by a modified direct vapour transport technique. The crystals were found to be semiconducting in nature. The influence of pressure on the electrical resistivity of the crystals grown was studied and the results explained on the basis of a transition from a predominantly two-dimensional material to a more three-dimensional one.