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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.

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 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.

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 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.

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.

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.

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.

The paramagnetic dc susceptibility was measured for CeAg 1− x In x . Its temperature dependence changes at the crystallographic transition temperature. It was calculated on the basis of the crystalline electric field (CEF). Tetragonally deformed CEF on 4f electrons was found to be shielded by the split 5d conduction electrons. The susceptibility in the tetragonal phase was well fitted by cubic CEF with conduction polarization.

Magnetic measurements have been performed on rare earth intermetallic compounds PrAg 1- x In x with the CsCl structure at room temperature for x ⩽ 0.7. A small substitution of In for Ag in PrAg which is antiferromagnetic stablizes a ferromagnetic phase and T C increases with increasing x in the region of x x ⩽ 0.35 which undergo a crystallographic transformation; the compounds are antiferromagnetic below T t and ferromagnetic between T t and T C . The T C decreases abruptly with increasing x and the antiferromagnetic phase is stable for x ⩾ 0.4. The magnetic properties are discussed in association with the state of conduction electrons.

Magnetic characteristics in RMn 2 Ge 2 with a layer structure have been studied by measurements of magnetization, electrical resistivity and neutron diffraction. Ferrimagnetic, antiferromagnetic, weak ferromagnetic and paramagnetic behaviours are observed in the sequence of increasing temperature. The transition from ferrimagnetic to antiferromagnetic states is found to be of first order with a hysteresis of 1 deg.