Superconductivity in polymeric sulfur nitride (SN)x at high pressure

Investigations of the pressure dependence of the superconducting transition temperature T_c up to 17 kbar, and of the normal conductivity up to 50 kbar are reported. It is observed that below 8 kbar, the value of T_c increases linearly with the pressure. In addition, there is a significant drop of T_c at about 9 kbar which may be due to a phase transition.     

Pressure dependence of the Néel temperature in CeMg and CeZn

Magnetization measurements have been carried out under hydrostatic pressures up to 6 kbar and constant magnetic fields (10 kOe) in CsCl-type compounds: CeMg and CeZn. a decrease in the Néel temperature, T_N, with increasing pressure is observed in both compounds (dT_N/dp=- 0.2 and -0.17 K kbar^-1 respectively in CeMg and CeZn). The relative decrease of T_N has a similar order of magnitude to that found in other cerium compounds with Kondo-type properties.     

Effect of hydrostatic pressure on the Curie temperature of the Heusler alloys Ni2MnZ(Z = Al,Ga, In,Sn and Sb)

The pressure derivative of the Curie temperature dT_c/dp of the Heusler alloys Ni₂MnZ(Z = Al, Ga, In, Sn and Sb) has been obtained from the results of temperature dependence of initial permeability under pressure up to about 6 kbar. For all alloys the Curie temperatures increase linearly with increasing pressure at the rate of dT_c/d_p: +0.7 K/kbar for Ni₂MnAl, +1.0 K/kbar for Ni₂MnGa, +0.9 K/kbar for Ni₂MnIn, +1.4 K/kbar for Ni₂MnSn and +4.1 K/kbar for Ni₂MnSb. On the basis of these results, the interatomic dependence of the exchange interaction for Heusler alloys is discussed. The magnetic susceptibilities of those alloys are also reported.     

The pressure dependence of the néel temperature in FeF2

A Mössbauer measurement of the pressure dependence of the Néel temperature in FeF₂ is reported. Up to the maximum pressure of 50 kbar T_N increases at the rate of 0.27 ± 0.03°K/kbar. When this pressure dependence is converted to volume dependence, the result, d In T_N/d In V = 3.2 ± 0.3, is found to obey the $\text{“10}\text{3}$ rule” established by Bloch for a wide variety of antiferromagnetic insulators.     

Uniaxial piezoresistance measurements on magnetite

The dependence of the Verwey temperature T_v on the uniaxial pressure P was determined. It was found that along the [111] axis dT_v/dP ≈ 10K/kbar while along the [110] and the [001] axes, dT_v/dP ≈ 1 K/kbar. The results emphasize the important role played by the rhombohedral distortion in the Verwey transition.     

Effect of hydrostatic pressure on the Neel temperature and the electrical residual resistivity of α-manganese

The electrical resistivity of α-Mn was measured from 4.2 K to 290 K at pressures up to 8 kbar. The residual resistivity was found not to depend on pressure. The Néel temperature decreases linearly with pressure at a slope dT_N/dP = − 1.7 ± 0.2 K/kbar.     

Superconductivity and calorimetric studies of Pr1.85Ce0.15CuO4+δ under different annealing conditions

Polycrystalline samples of electron-doped Pr_1.85Ce_0.15CuO_4+δ have been prepared under different annealing conditions and investigated by means of X-ray-diffraction, oxygen content analysis, electrical resistivity, magnetic susceptibility and low temperature specific heat measurements. X-ray-diffraction patterns show that samples contain a single T′ phase. The superconducting transition temperatures T_cm taken with the onset of diamagnetism in magnetic-susceptibility measurements are 20 and 19.5 K for sample annealed in flowing Ar gas and in vacuum (∼10⁻³ torr), respectively. The data of the samples, which are annealed in flowing Ar gas, show clear evidence for an αT² term at zero magnetic field in superconducting electronic specific heat, and are consistent with d-wave superconductivity. However, this behavior is not observed in the other sample, which is annealed in vacuum. These results indicate that different heat treatments affect the oxygen content, homogeneity, superconducting transition temperature T_c, superconducting volume fraction, and the superconducting pairing symmetry of Pr_1.85Ce_0.15CuO_4+δ.     

Pressure dependence of the superconducting transition temperature of a (Mo0.6Ru0.4)86B14 metallic glass

We have studied the pressure dependence of the superconducting transition temperature of amorphous (Mo_0.6Ru_0.4)₈₆B₁₄ for hydrostatic pressures up to P ～ 9 kbar. The transition temperature T_c decreases with pressure at a rate dT_c/dP=-(9±1) mK kbar^-1. We estimate the Grüneisen parameter and the volume dependence of the electron-phonon coupling constant.     

Pressure effect on the anomalous electrical conductivity of magnetite

The temperature dependence of the electrical conductivity of magnetite was measured under hydrostatic pressure up to 18.4 kbar. It is found that the temperature of the conductivity maximum in the high temperature phase is more rapidly reduced by pressure (dT_m/dP = -4.1 K/kbar) than the Verwey temperature (dT_v/dP = -0.27 K/kbar). The discontinuous change of the conductivity at T_v appears to increase with applied pressure as a result of a lowering of T_m.     

LaAg under hydrostatic pressure: Superconductivity and phase transformation

The electrical resistivity of LaAg has been measured from 1–300 K at hydrostatic pressures to 12.4 kbar and the superconducting transition temperature T_c determined inductively to 23 kbar. For P ? 6.2 kbar a lattice transformation is observed at a temperature T_M which increases rapidly with pressure. T_c shows an oscillatory pressure dependence, increasing initially from T_c (0) = 1.062 K. There is no obvious correlation between the pressure dependence of T_M and T_c.     

Effect of pressure on the Curie temperature of CoCr2O4

The pressure effect on the Curie temperature T_c of CoCr₂O₄ was measured under pressures up to 11.5 kbar. The pressure derivative of T_c is found to be +0.25 K/kbar. On the basis of this result, the relationship between the magnetic transition temperature and volume is discussed.     

Superconductivity in Nb.95Ta.05Se3

We have measured the resistivity of NbSe₃ doped with 5% Ta from room temperature down to 0.5K and compared our results with similar measurements on pure NbSe₃. The pure sample remains normal to the lowest temperature (0.5K), whereas the doped sample has a sharp transition to the superconducting state with T_c = 1.5 ± 0.2 K. Measurements of the critical magnetic field indicate that the Ta doped samples are homogeneous, anisotropic three dimensional superconductors.     

Effect of pressure on the superconducting transition temperature of the (Y1.2Ba0.8)4Cu4O16−δ ceramic compound

The superconducting transition temperature T_c, detected by the Meissner effect, of the single-phase (Y_1.2Ba_0.8)₄Cu₄ O_16−δ ceramic compound has been studied under hydrostatic pressure up to 3.4 kbar. The T_c increases with the increase of pressure at a rate of 1.5 K/kbar. The observed pressure behaviour of T_c is discussed with reference to a crystal structure and a cooperative bipolaron tunneling induced by Jahn-Teller distortions.     

Exponential Increase in the Resistivity upon Cooling and Superconductivity in Indium-Doped Pb<Subscript>0.45</Subscript>Sn<Subscript>0.55</Subscript>Te

We have analyzed the temperature and magnetic-field dependences of resistivity ρ(T, H) of semiconducting compound Pb_0.45Sn_0.55Te doped with 5 at % In under a hydrostatic compression at P < 12 kbar. It is found that the temperature dependence ρ(T) at all pressures at T < 100 K is exponential with the activation energy decreasing upon an increase in pressure; this is accompanied with a superconducting transition on the ρ(T) and ρ(H) dependences at P > 4.8 kbar at T > 1 K (T _c = 1.72 K at a level of 0.5ρ _N at P = 6.8 kbar). We consider the model describing the low-temperature “dielectrization” of the semiconducting solid solution and the formation of the superconducting state upon an increase in the hydrostatic compression P > 4 kbar.     

Pressure effects on the magnetic transition temperatures of NiS2

Both antiferromagnetic (T_N) and weak ferromagnetic (T_c) transition temperatures of NiS₂ have been measured under pressure up to 18.4 kbar. Values of dT_N/dP=(0.9 ± 0.1) deg/kbar and dT_c/dP=(0.4 ± 0.1) deg/kbar are obtained. The present results allow estimates of the magnetic Grüneisen constant γ_m = - d ln T_N/d ln V of (26±5) and of the entropy change of (1.4±0.5) J/mol·deg at the first order transition temperature T_c.     

The magnetic susceptibility of the high temperature superconductor La1.85Sr0.15CuO4 under hydrostatic pressure

The superconducting transition temperature (T_c ≅ 36 K) of single-phase La_1.85Sr_0.15CO₄ increases under hydrostatic pressure at the rapid rate +0.28 K/kbar (+0.78 %/kbar), whereas the Pauli susceptibility at 70 K changes by less than 0.2 %/kbar. This result provides evidence that in this compound the electronic density of states is not the predominant factor determining the anomalously high values of either T_c or its pressure derivative.     

Antiferromagnetic metallic state of NiS2

The neutron diffraction experiment we have made on NiS_1.91 single crystal under increasing pressure (0<P<30 kbar) indicates a constant increase of the Néel temperature of the sample. For high pressures (P>20 kbar) and low temperatures the sample is in an antiferromagnetic metallic state as suggested by theoretical considerations for a Mott-Hubbard insulator. The pressure dependence of the second magnetic transition in NiS₂ (T = 31 K for P = 0) is also reported.     

Dependence of temperature-dependent electrical resistivity of SrIrO3 on hydrostatic pressure to 9.1 kbar

Non-Fermi-liquid behavior and close proximity to a quantum critical point in the 5d transition metal iridate SrIrO₃ at ambient pressure motivate our search for possible anomalous behavior in its transport properties under pressure. The electrical resistivity in the ab-plane of a single crystal of SrIrO₃ has been measured over the temperature range 1.35–285 K at both ambient and 9.1 kbar hydrostatic pressure. The resistivity decreases slightly over the entire temperature range, but no superconducting transition or changes in the non-Fermi-liquid behavior are observed under pressure. It is estimated that significantly higher pressures are likely required before sizable changes in the properties of SrIrO₃ will occur.     

Magnetic properties and hydrostatic pressure effect on the curie temperature of (Co,Mn)2B amorphous alloys

The temperature dependence of magnetization and magnetic susceptibility and hydrostatic pressure effect on the Surie temperature (dT_c/dP) are measured for (Co_1-xMn_x)₂B (0?x?0.4) amorphous alloys and the results are compared with those of crystalline compounds with the same composition. The Curie temperature decreases linearly with an increasing Mn content but magnetization shows a maximum around x=0.15. The reciprocal magnetic susceptibility of all the prepared alloys obeys the Curie-Weiss law above T_c. The magnitude of the negative value of dT_c/dP decreases linearly with increasing x from about 1.1 K/kbar (x=0) to zero (x=0.4), the composition dependence of which is opposite to that of the crystalline compound. The composition dependence of the average magnetic moment per transition metal atom and the Curie temperature and dT_c/dP are analysed on the basis of the local environment and the pair order interaction mode, respectively.     

The pressure effect on the CDW-transition temperatures in 1T-TaS2

The pressure dependence of the two CDW transition temperatures (T_d1? 350 K and T_d2 ～ 190 K) in 1T-TaS₂ has been investigated by measuring the resistivity up to 5 kbar. It is found that the thermal hysteresis of the phase transition at T_d2 is very sensitive to the pressure and is interpreted by the phenomenological Landau theory including cubic term.