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The compounds of EuNi(Si1−xGex)3 order antiferromagnetically. At the temperature TC below the Ńeel temperature TN, EuNiSi3 (x = 0) shows an additional magnetic transition into ferro-magnetic state. TN decreases monotonously with increasing the Ge composition x. The Curie temperature TC decreases rapidly with increasing x and vanishes at the critical composition x ≈ 0.3. We have measured the electrical resistivity and thermopower of EuNi(Si0.8Ge0.2)3, which is a compound near to the boundary between the ferromagnetic and antiferromagnetic ground states in the phase diagram for EuNi(Si1−xGex)3 system, under pressures up to 1.8 GPa at temperatures from 2 to 300 K. The anomalies in ρ(T) and S(T) curves of EuNi(Si0.8Ge0.2)3 are observed at TC = 16 K and TN = 34 K at ambient pressure. Both TC and TN increase linearly with increasing pressure. The temperature variations of ρ and S of EuNi(Si0.8Ge0.2)3 at P = 1.8 GPa are almost the same as those of EuNi(Si0.9Ge0.1)3 (x=0.1) at ambient pressure, revealing that the effect of pressure on TN and TC is the same as that of the increase of Si concentration. The pressure and atomic composition dependences of the magnetic transition temperatures TN and TC can be expressed by using the Gruneisen parameters. These results indicate that the changes of TN and TC are attributed to the change of atomic volume induced by the applying pressure or the atomic substitution.

The electrical resistivity ρ and the thermopower S of Ho(Co1−xAlx)2 alloys (x = 0 to 0.2) were measured at temperatures from 2 K to 300 K in magnetic fields up to 10 T. While ρ(T) and S(T) of pure HoCo2 reveal abrupt changes at the magnetic ordering temperature TC, indicating a firstorder transition, the temperature variations of both properties across the ordering temperature in Ho(Co1−xAlx)2 alloys clearly show that the type of magnetic transition changes under substitution of Al for Co from first order to second order around x ≈ 0.06. ρ(T) of the Al-substituted samples (x = 0.15 and 0.2) has a very unusual variation at temperatures below TC: in contrast to the expected and usually-observed decrease of ρ(T), the resistivity of Ho(Co1−xAlx)2 alloys (x = 0.15 and 0.2) increases at temperatures below TC. Moreover, the magnetoresistance of these alloys is positive around TC; this is also in a sharp contrast to the usually observed negative magnetoresistance. We show that the anomalous resistivity and magnetoresistance in these alloys are related to the metamagnetic instability of the Co 3d subsystem and to the fluctuating local magnetic susceptibility due to atomic substitution. Due to this fluctuating local magnetic susceptibility, the uniform exchange field of 4f moments induces a non-uniform polarization of the 3d system, with static spatial fluctuations of the local magnetization. This static magnetic disorder gives an additional contribution (ρm) to the electrical resistance in the alloys at temperatures below TC. The degree of this disorder changes with decreasing temperature, resulting in specific variation of ρm with temperature.

The electrical resistivity ρ and the thermopower S of pseudo-binary Y1−x Nd x Co2 alloys have been measured at temperatures from 2 to 300 K under pressures up to 3.5 GPa. NdCo2 is a ferromagnet with a Curie temperature T C of 98 K. In the ferromagnetic phase, it undergoes a 4f spin-reorientation transition at T R = 40 K. At this transition, the easy direction of 4f magnetization is changed from [100] at temperatures above T R to [110] below T R. The system phase diagram T C(x, P) and T R(x, P) is inferred from the temperature dependencies of the electrical resistivity and the thermopower. The Curie temperature of the alloys, TC decreases with decreasing Nd concentration x and vanishes around x c = 0.3. Above x c, the Curie temperature decreases with increasing pressure. The spinreorientation temperature weakly depends on the composition and on the pressure until it merges with T C. There is a large region of the phase diagram, partly overlapping with the ferromagnetic phase, where the cobalt 3d electron system is non-uniformly magnetized due to spatial fluctuations of the 4f-3d exchange field related to a random distribution of Nd 4f magnetic moments over the R sublattice. In this region, large static 3d magnetic fluctuations govern the electronic transport.

Ferromagnetic-phase transition in spinel-type CuCr 2 Te 4 has been clearly observed. CuCr 2 Te 4 is a telluride–spinel with the lattice constant a = 11.134 A , which has been synthesized successfully. The heat capacity exhibits a sharp peak due to the ferromagnetic-phase transition with the Curie temperature T C = 326 K . This value of T C corresponds exactly to that of the negative peak of d M /d T in low field of 1.0 Oe. The magnetic susceptibility shows the Curie–Weiss behavior between 380 and 650 K with the effective magnetic moment μ eff = 4.14 μ B /Cr-ion and the Weiss constant θ = + 357 K . The low temperature magnetization indicates the spin-wave excitations, where the existence of first term of Bloch T 3/2 law and the next T 5/2 term are verified experimentally. This spin-wave excitation is detected up to approximately 250 K which is a fairly high temperature.

The electrical resistivity ρ and thermopower S of Heusler compounds Fe 3- x V x Al have been measured at the temperature range from 1.5 to 300 K at magnetic fields up to 15 T. The measurements of ρ and S in the high temperature range up to 800 K have been performed. ρ and S show a semiconducting behavior at high temperatures, and the obtained experimental energy gap increases almost linearly with increasing V concentration x . S is positive for x

The phase formation, the resistivity and the thermopower of amorphous Cr0.15Si0.85, and nanocrystalline CrSi2-Si thin film composites have been studied. The films were produced by a magnetron sputtering of a composite target onto unheated substrates with subsequent crystallization of the film at high temperatures. As the film composite develops under the heat treatment from the initial amorphous state into the final polycrystalline material, two percolation thresholds were found. At first, the percolating cluster of nanocrystalline CrSi2 is formed. However, this cluster is destroyed with further annealing due to crystallization and redistribution of Si. The composite films which are close to this insulating threshold reveal a strongly nonlinear conductivity. The conductivity increases with the current by two orders of magnitude.

Resistivity p and thermopower S of spinel compounds Cu 1-x Zn x Ir 2 S 4 with x < 0.3 have been measured at temperatures from 1.5 to 1000 K and under high pressures of up to 2 GP. The compounds undergo metal-insulator transition (MIT) at a temperature T MI which decreases with increasing x. In the low-temperature insulating phase, the resistivity of the compounds follows to the relation ρ ∼ exp(T*/T) 1/2 , suggesting Efros-Shklovskii variable range hopping conductivity mechanism. The inverse of the effective activation energy I/T*, as it was obtained from p measured under hydrostatic pressure (P) for x = 0, decreases linearly with P supporting the Efros-Shklovskii model. Thermopower S is positive in the insulating phase. It increases with temperature having a maximum somewhat below T MI , and abruptly decreases at T MI . In the metallic phase S is positive and linear in T up to at least 900 K. The maximum value of S in the insulating phase is about 4 times large for x = 0.1 compared to x = 0, and it quickly decreases with increasing x. It is found that the transport properties of CuIr 2 S 4 are strongly dependent on the sample preparation conditions.

The measurements of the electrical resistivity ρ and the thermopower S of single crystal EuCo2P2 have been performed at temperatures from 1.5 to 300 K under hydrostatic pressures up to 3 GPa and in magnetic fields up to 10 T. The temperature dependences of ρ and S show drastic changes at a critical pressure Pc, which indicates a large modification of the electronic structure around the Fermi level due to the valence transition from Eu to Eu. In the low-pressure phase with magnetic Eu and nonmagnetic Co, the magnetic field dependences of ρ and S show sudden decrease at B ≈ 7 T, implying a metamagnetic transition. On the other hand, no drastic change in ρ(B) and S(B) curves is observed in the high-pressure phase with nonmagnetic Eu and magnetic Co.

In this paper we describe an experimental set-up for simultaneous measurements of thermopower and electrical resistivity at temperatures from 100 K to 1300 K. Optimal configuration of electrodes and original mechanical contacts of thermocouples, current leads and potential probes with the sample make it possible to measure a large variety of materials and result in greater flexibility with respect to the sample form and dimensions. Both bulk and thin film samples with resistances in the range from 0 Ω up to 200 kΩ (1 GΩ in case of the resistivity measurement) can be investigated. Precision and high reliability of the system have been proven during more than three years of use. The resistivity and thermopower of pure Pb, Cu and Ni, and a Cr-Si thin film composite are presented as test materials to demonstrate the possibilities and accuracy of this experimental set-up.

Resistivity $(\ensuremath{\rho})$ and thermopower (S) of spinel-type compounds ${\mathrm{CuIr}}_{2}{\mathrm{S}}_{4}$ and ${\mathrm{CuIr}}_{2}{\mathrm{Se}}_{4}$ have been measured at temperatures from 2 to $900\mathrm{K}$ under magnetic field from 0 to $15\mathrm{T}.$ The thermopower is positive in the metallic phase of both compounds at high temperatures, as well as in the low-temperature insulating state of ${\mathrm{CuIr}}_{2}{\mathrm{S}}_{4}.$ The positive thermopower of the insulating phase implies p-type charge carriers, in agreement with the recent photoemission results. The low-temperature resistivity of ${\mathrm{CuIr}}_{2}{\mathrm{S}}_{4}$ is in good agreement with the Efros-Shklovskii variable-range hopping conductivity mechanism: $\ensuremath{\rho}={\ensuremath{\rho}}_{0}\mathrm{exp}[{(T}^{*}{/T)}^{1/2}].$ The most striking result is that the resistivity of the metallic phases is well described by an exponential-type temperature dependence in a wide temperature range from $2\mathrm{K}$ to at least $900\mathrm{K}.$ This unusual result for metals type of the resistivity temperature dependence, as well as other features in the transport properties, imply a nonconventional conductivity mechanism. The magnetoresistivity $\ensuremath{\Delta}\ensuremath{\rho}$ is positive and proportional to ${H}^{2},$ while magnetothermopower $\ensuremath{\Delta}S=S(H,T)\ensuremath{-}S(0,T)$ is very small for both compounds at all temperatures.

The diamagnetic susceptibility in CuIr 2 S 4 is independent of temperature up to just below metal–insulator transition temperature. If activation of electrons to higher levels occurs with breaking dimer pairs, the residual electrons at the dimer position and the activated electrons to the anti-bonding orbital make localized free spins giving a Langevin paramagnetism. Assuming no magnetic interaction between the localized free spins, the susceptibility is calculated using the energy gap obtained from the conductivity assumed to be a conventional semiconductor. The calculated results cannot explain the temperature-independent diamagnetism. The real energy gap is too large for thermal electron activation, however, conduction is induced thermally over several orders of magnitude within insulating phase. From the above results, we claimed new conduction mechanism named traveling dimer conduction: dimer shifts its position by electron hopping to neighbor position without electron activation over the energy gap.

We report on low-temperature transport in magnetic conductors with structural disorder. The primary motivation for this work was large positive magnetoresistance (MR) found in magnetically ordered ground state of some itinerant metamagnetic alloys. The positive MR suggests that external magnetic field enhances static magnetic disorder δ M → ( r → ) = M → ( r → , T , H → ) - 〈 M → ( r → , T , H → ) 〉 , whereas standard approach assumes suppression of magnetic fluctuations by external magnetic field as a source of negative MR. We review the relevant experimental data, mostly the properties of RCo 2 -based alloys and discuss a phenomenological model developed for the interpretation of the experimental results. This model includes new mechanism of magnetoresistivity in structurally disordered itinerant metamagnetic alloys.

We report magnetic susceptibility and electrical resistivity under high pressure on polycrystalline Fe 2+ x V 1− x Al, which exhibits the ferromagnetic transition at x > 0 . The pseudogap band structure, magnetic defects and lower number of conduction carrier seem to result in the spin fluctuation, the enhancement of thermoelectric power and other unique properties in this system. On the other hand, the excess V-atom brings about the variable range hopping conduction at lower temperature that is affected by external pressure. The pressure effects on the transition temperature, T c , and magnetization at low temperature reveal that the magnetism can be described by the self-consistent renormalization (SCR) theory.

Thermopower of Y 1 - x Gd x Co 2 pseudobinary compounds has been measured at temperatures from 1.5 to 300 K under hydrostatic pressure up to 2 GPa and in magnetic field 0–15 T. In the inhomogeneous and paramagnetic regions of the phase diagram the main contribution to the electronic transport is related to the strong static magnetic fluctuations, which arise due to interplay of structural disorder within Gd-sublattice and Co-3d itinerant electron metamagnetism. This complex magnetic disorder brings about novel transport phenomena, such as anomalous positive magnetoresistance found in ferrimagnetic state of the alloys. The low-temperature thermopower is almost independent of alloy composition in the ferrimagnetic range of the phase diagram ( x > 0.3 ) indicating that the alloying does not change electronic structure of the compounds in a close vicinity of Fermi energy. However, the thermopower shows substantial variation with the composition in the inhomogeneous and in the paramagnetic regions of the phase diagram reflecting evolution of the magnetic structure with the composition.

The oxygen content dependence of 63Cu NQR at the Cu(1) site and proton NMR have been measured in the antiferromagnetic phase of powdered samples of hydrogen-doped YBa2Cu3O6+xHy (0.07 1H NMR is a single line and the line width increases below 15 K due to magnetic interactions. The enhancements of T1 -1 and T2 -1 of 63Cu(l)NQR occur around 35 and 15 K, respectively. These enhancements increase with increasing oxygen concentration. The maximum values of T1 -1 and T2 -1 for the sample with x = 0.17 reach 200 sec-1 and more than 7 msec-1, respectively. The predominant source for the relaxation mechanism of 63Cu(l) NQR and the line broadening of 1H NMR are found to be the fluctuating magnetic field due to the staggered Cu2+ moments.

Thermopower S and resistivity ρ of Y 1 − x R x Co 2 ( R = Er , Ho) compounds have been measured in the temperature range from 1.5 to 300 K under magnetic fields up to 15 T. Strong enhancement of resistivity and fundamental changes in temperature variation of thermopower are observed at low temperatures in the compounds within the composition range where uniform Co 3d magnetization collapses. The magnetic state of Co 3d electrons has a dominant effect on the characteristic behavior of S and ρ in these compounds.

The superconducting energy gap of CeRu{sub 2} has been studied by break-junction tunneling. The observed gap values 2{Delta}(0)=1.9{endash}2.6 meV with T{sub c}=5.4{endash}6.7 K give the ratio 2{Delta}(0)/k{sub B}T{sub c}=4.1{endash}4.4, indicating a strong-coupling superconductor. The temperature dependence of the gap value is in good agreement with the BCS prediction. {copyright} {ital 1997} {ital The American Physical Society}

The saturation magnetization of polycrystalline CeAg 1− x In x measured in magnetic fields up to 15 T at 1.5 K is about 1.5 μ B and 1.0 μ B for x ⩽0.2 and x ⩾0.3, respectively. Reversal of the crystalline electric field (CEF) occurs from Γ 8 ground state to Γ 7 . The susceptibility can be approximated by the cubic CEF in the tetragonal phase, however, it cannot be represented in the cubic phase for x >0. The atomic shifts in the tetragonal phase widen the volume available for Ce, corresponding to reduction of about 13 kbar pressure. The results are discussed with the 5d—e g conduction band population.

Low temperature a.c.-susceptibility measurements of the intermetallic compound TmCo 2 under various external magnetic fields up to 1.5 T are reported. Two magnetic phase transitions were found at the temperatures 3.4 and 3.8 K. The origins of the transitions are discussed on the basis of quadrupolar as well as magnetic interactions.

Magnetoresistance, thermopower, Hall resistivity, ac susceptibility and magnetization have been measured for CeRu 2 in the normal and superconducting phases. In the normal state, there is a magnetic anomaly at 50 K, which is presumably due to development of antiferromagnetic order. The H-T superconducting phase diagram obtained from ac susceptibility indicates the possibility of multiple superconducting phases.

Thermopower S and electrical resistivity ρ of cubic Laves phase pseudo-binary compounds Y1−xErxCo2 were measured from 2 to 300 K in magnetic fields up to 15 T . S and ρ show a strong field dependence in a vicinity of the magnetic ordering temperature. The reduction of the exchange magnetic field Bexc acting on Co 3d electrons by Y substitution for Er results in a separation of magnetic transition temperatures of Er and Co subsystems in Y0.4Er0.6Co2. The collapse of the itinerant Co 3d moments of Y0.4Er0.6Co2 is induced by applying external magnetic field about 10 T .

Thermopower S and resistivity ρ of cubic Laves phase compound ErCo2 were measured from 2 to 300 K in magnetic fields up to H=15 T. ErCo2 shows a first-order magnetic transition from paramagnetic to ferrimagnetic state at Curie temperature Tc≈32 K, where the sharp jump in S(T) curve was observed with increasing temperature. Tc increases with increasing H. The magnitude of the jump of S(T) at the first-order magnetic transition increases with increasing H in magnetic field up to 3 T. At higher fields, S(T) curve shows a double transition due to separation Er and Co ordering.

Magnetization curves [MC] and temperature dependence of the AC susceptibility [TS] were measured in the superconducting phase of CeRu 2 with T c =6.55 K in zero field. For fields higher than 0.8 T in [TS], the superconducting susceptibility behaves normally up to the lowest transition temperature T cL where it decreases suddenly; the field-induced reentrant superconductivity occurs at T cL and breaks very sharply to the normal state at T cH (the highest transition temperature). In [MC], an anomaly appears when the magnetization reaches to the extrapolated magnetization of the normal state at H R (reentrant field). Magnetization drops suddenly to negative in the field-increasing process for temperatures below 3.9 K, and it only increases for temperatures above 4.0 K. Reentrant superconductivity occurs between, H R and H c2 . The reentrant phase has positive magnetization in the background.

Thermopower (S), resistivity (ρ), and AC susceptibility of Y 1 xGdxCo2 alloys (0 ≤ x ≤ 1) have been measured at temperatures of 2K-300 K in magnetic field from 0 to 15 T. There are 4 composition regions on the phase diagram of Y 1 x Gd x Co 2 : Kondo-type behavior is observed at 0 < x ≤0.05, magnetic cluster glass state is found for x from about 0.07 to 0.12. At higher Gd content, x≥0.13 the ground state of the 4f localized moment subsystem is ferromagnetic. The magnetoresistivity (Δρ) shows unusual large positive values in the magnetically ordered phase 0.15 < x ≤0.3.

The temperature and the magnetic field dependencies of magnetoresistivity of paramagnetic RCo 2 compounds (R=Y, Lu, and Sc), and paramagnetic and weakly ferromagnetic Y(Al x Co 1− x ) 2 alloys (0⩽ x ⩽0.15) have been measured at temperatures of 2–300 K, in magnetic fields up to 15 T. The magnetoresistivity is positive in paramagnetic and in weakly ferromagnetic compounds at low temperatures. A simple phenomenological model is proposed to explain the results.

We present experimental results on thermoelectric power $(S)$ and electrical resistivity $(\ensuremath{\rho})$ of pseudobinary alloys $\text{Ho}{({\text{Al}}_{x}{\text{Co}}_{1\ensuremath{-}x})}_{2}$ $(0\ensuremath{\le}x\ensuremath{\le}0.1)$, in the temperature range 4.2 to 300 K. The work focuses on the effects of static (induced by alloying) and dynamic (induced by temperature) disorder on the magnetic state and electronic transport in a metallic system with itinerant metamagnetic instability. Spatial fluctuations of the local magnetic susceptibility in the alloys lead to the development of a partially-ordered magnetic ground state of the itinerant $3d$ electron system. This results in a strong increase of the residual resistivity and a suppression of the temperature-dependent resistivity. Thermopower exhibits a complex temperature variation in both the magnetically ordered and in the paramagnetic state. This complex temperature variation is attributed to the electronic density-of-states features in vicinity of Fermi energy and to the interplay of magnetic and impurity scattering. Our results indicate that the magnetic enhancement of the $\text{Co}\text{ }3d$ band in $R{\text{Co}}_{2}$-based alloys upon a substitution of Co by nonmagnetic elements is mainly related to a progressive localization of the $\mathrm{Co}\text{ }3d$ electrons caused by disorder. We show that the magnitude of the resistivity jump at the Curie temperature for $R{\text{Co}}_{2}$ compounds exhibiting a first-order phase transition is a nonmonotonic function of the Curie temperature due to a saturation of the $3d$-band spin-fluctuation magnitude at high temperatures.

Electrical resistivity of polycrystalline sample of CeRu2 was measured under quasi-hydrostatic pressure from 1. 5 to 8 GPa in the temperature range from 4 to 300 K. A new pressure induced phase transition appears above 5. 5 GPa. No temperature and pressure hysteresis was observed in the transition region. The transition temperature increases linearly with increasing pressure.

New mechanism of magnetoresistivity in itinerant metamagnets with a structural disorder is introduced basing on analysis of experimental results on magnetoresistivity, susceptibility, and magnetization of structurally disordered alloys $({\mathrm{Y}}_{1\ensuremath{-}x}{\mathrm{Gd}}_{x}){\mathrm{Co}}_{2}.$ In this series, ${\mathrm{YCo}}_{2}$ is an enhanced Pauli paramagnet, whereas ${\mathrm{GdCo}}_{2}$ is a ferrimagnet ${(T}_{\mathrm{c}}=400\mathrm{K})$ with Gd sublattice coupled antiferromagnetically to the itinerant $\mathrm{Co}\ensuremath{-}3d$ electrons. The alloys are paramagnetic for $xl0.12.$ Large positive magnetoresistivity has been observed in the alloys with magnetic ground state at temperatures $Tl{T}_{\mathrm{c}}.$ We show that this unusual feature is linked to a combination of structural disorder and metamagnetic instability of itinerant $\mathrm{Co}\ensuremath{-}3d$ electrons. This new mechanism of the magnetoresistivity is common for a broad class of materials featuring a static magnetic disorder and itinerant metamagnetism.

In this paper we describe an experimental set-up for simultaneous measurements of thermopower and electrical resistivity at temperature from 100 K to 1300 K. Optimal configuration of electrodes and mechanical contacts of the thermocouples, current leads and potential probes with sample make it possible to measure a large variety of materials and result in a flexibility with respect to the sample form and dimensions. Both, bulk and thin film samples can be investigated. The measurements can be done in vacuum or in an inert gas atmosphere. Samples with resistance varying from 0 /spl Omega/ up to 200 k/spl Omega/ (1 G/spl Omega/ in case of the resistivity measurement) can be measured. High precision and high reliability of the system have been proved during more than two years use. The resistivity and thermopower of pure Ni, CeB/sub 6/ heavy fermion compound and a Cr-Si thin film composite are presented as a test material to demonstrate the possibilities and accuracy of this experimental set-up.

The electrical resistivity (ER), Hall resistivity (HR) and thermoelectric power (TEP) have been measured for cubic SmAg 1− x In x . The temperature dependences of ER and TEP have sharp changes at T N for SmAg and at T t (the lower transition temperature) for x ⩽0.3. They have less pronounced changes at T c and T t for x >0.3. The paramagnetic values of HR and TEP decrease with increasing x .

The magnetization M, electrical resistivity ρ, thermopower S and specific heat C of EuNi(Si1-xGex)3 compounds have been measured at temperatures from 2 to 300 K. For the compounds of EuNi(Si1-xGex)3, we obtained an effective magnetic moment of μeff ~ 7.7 μB, which is close to the divalent Eu value of μeff =7.94 μB. All compounds of EuNi(Si1-xGex)3 order antiferromagnetically. The Neel temperature TN decreases monotonously with increasing the Ge concentration x from TN=49 K for EuNiSi3 to TN=14 K for EuNiGe3. In the low temperature region below TN, anomalies corresponding to an additional magnetic phase transition into ferromagnetic state for compounds with x 0.3 were observed. The Curie temperature TC rapidly decreases with increasing x and vanishes at x ≈ 0.3. It is found that the magnetic phase transition temperatures of TN and TC in EuNi(Si1-xGex)3 are strongly connected with the change of volume induced by the atomic substitution of Si by Ge.

The electrical resistivity ρ and thermopower S of spinel compound CuIrCrS 4 have been measured at temperatures from 20 to 300 K under hydrostatic pressure up to 2 GPa. No anomalies in the ρ and S curves were observed at the magnetic ordering temperature T ≈130 K at ambient pressure. ρ shows an unconventional semiconducting temperature dependence, which is expressed as ρ∝exp { ( A / T ) n }. The index n increases linearly from 1/4 to 1/2 with increasing pressure. S has a broad peak around 100 K and shows a metallic behavior at high temperatures. The temperature dependence of S under pressure below 1.0 GPa is represented as S ∝ T 1/2 in the low-temperature limit. These results imply that the low-temperature conduction of CuIrCrS 4 can be described in terms of the variable range hopping mechanism.

X-Ray powder diffraction method is used to investigate the effect of magnetic ordering and external magnetic field on crystal structure of Laves phase intermetallic compound ErCo 2 . The diffraction patterns were recorded at temperatures from 300 K down to 8.5 K in magnetic field up to 5 T. Distortion of the room-temperature cubic structure was found in magnetically ordered state below 32 K. The symmetry at low temperature is rhombohedral in agreement with literature results, or lower symmetry than it. However the symmetry of the unit cell increases to cubic in external magnetic field of 5 T.

Electrical resistivity of Y 1 - x Gd x Co 2 alloy system has been measured at temperatures from 2 to 300 K in magnetic field up to 15 T and under pressure up to 10 GPa. The compounds with the composition near to phase boundary between paramagnetic and ferromagnetic ground state ( x c ≈ 0.12 ) show strong enhancement of electrical resistivity at low temperatures. Large positive magnetoresistance was observed in ferromagnetic alloys in composition range 0.15 x 0.3 . The anomalous magnetoresistance as well as the composition dependence of the low-temperature resistivity were explained by an interplay of metamagnetic instability of Co 3d itinerant electrons and structural disorder within rare-earth sublattice. The pressure effect on electrical resistivity for Y 1 - x Gd x Co 2 at low temperatures is in agreement with the variation of magnetoresistance with the composition.

We present experimental results on thermopower of (Y1−xGdx)Co2 alloys at temperatures from 2 to 500 K in magnetic fields up to 15 T . The variation of thermopower with the alloy composition is explained as arising from a combination of structural disorder and itinerant metamagnetism of 3d electron system.

We discuss results on magnetoresistivity of structurally disordered alloys (Y 1− x Gd x )Co 2 . Large positive magnetoresistivity is observed in the alloys with magnetic ground state at temperatures T T c . This feature is directly linked to a combination of structural disorder and metamagnetic instability of itinerant Co-3d electrons.

Electrical resistivity and thermopower of Y1−xHoxCo2 alloys was measured from 2 to 300 K in magnetic fields up to 15 T . TC of HoCo2 increases with increasing magnetic field, however, the ordering temperature is not split into the ordering of Ho sub-lattice and the ordering of Co sub-lattice by the field contrary to the case of ErCo2.

The electrical resistivity and thermopower of light- and heavy-rare-earth-based pseudo-binary Y1-xRxCo2 (R = Nd, Gd, and Tb) alloys are measured at temperatures from 2 to 300 K under pressures up to 3.5 GPa. The resistivity and thermopower of Y1-xRxCo2 show unusual large variations with atomic substitution and pressure in the range of x

The resistivity ρ and thermopower S of CaB6 single crystal have been measured at temperatures from 2 to 1100 K in magnetic fields up to 15 T . Temperature dependence of ρ is expressed as [ρ(T)−ρ(0)]∝ exp [−(T ∗ /T) 1/2 ] for T⩽90 K and T1.7 for 90 K ⩽T⩽1100 K , where ρ 0 =232 μΩ cm . The magnitude of ρ and S is very large suggesting thin concentration of carriers. The temperature dependence of them suggests the conduction is metallic and electron type. ρ and S can be fitted on the basis of free electron model and obtained the Fermi level is situated near the bottom of an electron band with the Fermi energy of 80 K . The experimental and fitting results show this compound is semi-metallic. No scattering anomalies in temperature dependence of ρ were observed and also no sudden change of the Fermi surface accompanied with magnetic transition in S above 100 K including the region where it might be considered to have ferromagnetic transition.

We present experimental results on magnetotransport in (Y x Gd 1− x )Co 2 alloys, where the localized Gd-moments are coupled antiferromagnetically to the itinerant Co 3d electrons. The alloys are paramagnetic for x >0.85. The transport properties of the paramagnetic alloys show Kondo like anomalies. On approaching to the magnetic phase boundary from the paramagnetic region the resistivity reveals non-Fermi liquid (NFL) behaviour, indicating a presence of apparently gap-less magnetic excitations.

Electrical resistivity ρ and thermopower S of the Laves phase compound of NdCo2 has been investigated at temperatures from 2 K to 300 K. ρ has been measured under pressures up to 8 GPa and S has been measured under pressures up to 3 GPa. The magnetic transition temperature TC obtained by ρ measurement decreases with increasing pressure. The temperature Tmim where the thermopower S takes minimum at high temperature region increases linearly with increasing pressure. The high-temperature minimum of S is associated with a sharp peak in density of states related mainly to the Co 3d-electron density. Since the width of an itinerant electronic band depends on the extent of the corresponding overlapping of 3d orbitals, the pressure variation of Tmin can be attributed to the broadening of the peak width of 3d electron density of states.

The electrical resistivity ρ and thermopower S of the Heusler compound Fe 1.98 V 1.02 Al have been measured in the wide temperature range from 2 to 800 K, additionally applied magnetic fields up to 15 T at the temperature range from 2 to 300 K. No field dependence of ρ and S was observed, indicating that the magnetic ground state of Fe 1.98 V 1.02 Al is paramagnetic. ρ and S show the semiconducting behavior at high temperatures, and show the metal-like behavior at low temperatures. The temperature dependences of ρ and S can be represented by means of two channel conducting model.

The electrical resistivity ρ and thermopower S of the cubic Laves phase compounds Ho(Co 1- x Al x ) 2 ( x =0, 0.15 and 0.20) have been measured at temperatures from 2 to 300 K in magnetic fields up to 10 T. The measurements of ρ under pressures up to 3 GPa have been performed in the temperature range between 2 K and 300 K. Both ρ( T ) and S ( T ) of the pure HoCo 2 reveal abrupt changes at the magnetic ordering temperature T C , indicating the first order transition. ρ( T ) of the Al substituted samples ( x =0.15 and 0.20) show anomalous behavior in the form of an increase below T C . The variations of ρ and S at T C clearly indicate that the type of the magnetic transition changes under substitution of Al for Co from the first order to the second order. The residual resistivity of Ho(Co 1- x Al x ) 2 shows a rapid increase with increasing x . T C increases linearly for x < 0.15, having a maximum at x ≈0.15 and decreases with further increase of x . The peculiar x dependence of T C and the anomalous behav...

The resistivity ρ of CuIr 2 S 4 and CuIr 2 Se 4 have been measured at temperatures from 2 to 300 K under hydrostatic pressures up to 2 GPa. The conductivity σ at low temperature in the insulating phase of CuIr 2 S 4 is expressed as follows: σ =exp[−( T i * / T ) 0.5 ]. The pressure dependence of the activation energy and metal–insulator transition temperature give evidence that Coulomb correlations are important. Appearance of the insulating phase in CuIr 2 Se 4 is at a lower pressure than it had been assumed. The total resistivity under pressure can be represented as the resistivity in two parallel channels: the metallic resistivity which is exponentially dependent on temperature and the semiconducting one. The effective cross-section of the semiconducting channel rapidly increases with pressure above 1 GPa.

The resistivity (ρ) and the thermopower (S) of spinel-type compounds CuIr2S4 and CuIr2Se4 have been measured at temperatures from 2 to 900 K under magnetic field from 0 to 15 T. The thermopower of both compounds is positive in the metallic phase except for the low-temperature region in CuIr2Se4. It is also positive in the insulating state of CuIr2S4, implying p-type charge carriers, in agreement with the recent photoemission results. The low-temperature resistivity of CuIr2S4 is well described by Efros–Shklovskii variable-range hopping conductivity mechanism: ρ=ρ 0 exp [(T ∗ /T) 1/2 ] . The most unusual feature of the transport is that the resistivity of both compounds in the metallic state reveals an activation type of the temperature dependence.