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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 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 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.

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.

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.

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.

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 .

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 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.

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.

Thermoelectric power (S) and electrical resistivity (ρ) of Y(Co1−xAlx)2 alloys with x in the range of 0–0.15 have been measured at temperatures from 2 to 300 K, in the longitudinal magnetic field of 0–15 T. The present results show that there is a rapid variation of the transport properties and a peculiarity in the dependency of lattice parameter on x at x≈0.03; however, no change of the lattice symmetry has been detected. Although the precise mechanism of the anomaly at x≈0.03 has not been understood, the results suggest that it is related to a change in the localization of the Co–3d electrons caused by the increasing Co–Co separation and by the disorder within the Co-sublattice in the Y(Co1−xAlx)2 alloys.

Electrical resistivity of cubic Laves-phase compound CeRu 2 has been measured from 3 to 300 K under the quasi-hydrostatics pressure P from 1.5 up to 8 GPa. X-ray diffraction was performed at room temperature under the pressure up to 15 GPa. Temperature dependence of electrical resistivity ρ ( T ) shows no anomaly at pressures below 5 GPa and resistivity decreases with increasing pressure. However, ρ ( T ) curves, measured under the pressure above 5.5 GPa, reveal an abrupt decrease at critical temperature T a . This indicates that a new phase is induced by the pressure. T a shows a large pressure dependence: Δ T a /Δ P =59.2 K/GPa. According to the X-ray data, the phase transition above 5.5 GPa is a structural-phase transition.

The resistivity of CeRu 2 was measured under high pressure up to 1 GPa. The pressure dependence of superconducting transition temperature T c of CeRu 2 is negative by a rate of ΔT c /Δp = − 0.47K/GPa for p ⩽ 0.5GPa and is positive for 0.5GPa 1GPa by a rate of 0.33 K/GPa. The room temperature resistivity increases after the cooling of the sample down to 4 K for p ⩾ 0.6GPa, indicating a phase transition which induces the change of pressure derivatives of the superconducting transition temperature.

The electrical resistivity (ϱ) and thermopower (S) of exchange-enhanced paramagnetic compound YCo2 were measured in the temperature range 2–300 K in a longitudinal magnetic field (H) from 0 to 15 T. The magnetic field was applied parallel to the electrical current or to the temperature gradient to reduce the effect of the classical (Lorentz force driven) contributions to the magnetoresistivity and magnetothermopower. The temperature dependent thermopower has a deep minimum around 20 K. The magnetothermopower ΔS = S(0) - S(H) at low temperatures is negative, and shows a minimum at almost the same temperature as that of S(0). Magnetoresistivity is positive at low temperatures. The discussion of the experimental results is focused on the low-temperature behaviour of S(T) and ϱ(T).

H c1 and H c2 were accurately estimated in U 6 Fe by ac susceptibility. T c and two anomalies were found at 4.10, 3.7 and 2.7 K, respectively. H c1 was analyzed by Bean's model and found to be 0.13 T at T = 0 K, which is an order of magnitude larger than that obtained by SQUID with a residual field and field distribution of the SQUID meter. H c2 is 6 T at 0 K.

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.

Two superconducting transitions were observed in U 6 Co by magnetic measurements, T cH =2.69 K and T cL =2.24 K . The behaviors of the T c ' s are different above and below H =1 T . The effect of field cooling (FC) at 1.92T on H c 2 is positive, i.e. FC increases the transition temperature.

Temperature dependence of the magnetic susceptibility was measured for CeRu2 in fields up to 2T. Tc=6.55K in zero field. It was found the Tc splits into 3 peaks for H>0.8T. The transition of the highest Tc (TcH) is very sharp. Temperature hysteresis was not observed on TcH, but observed on the other two.

Giant magnetic coercivity over 90 kOe has been found in cubic Sm pseudobinary compounds with CsCl type structure. The coercive force C H varies with the fourth power of the remanent magnetization below T t = 27K and with the second power of it above T t for SmAg 0.6 In 0.4 . A long annealing of 50 days results in a drastic reduction of C H and the critical field for SmZn 0.8 Cu 0.2 . On the other hand, the orthorhombic Sm compounds exhibit very small coercivity. The crystalline anisotropy and the wall pinning effects seem to be very important for the coercivity of these pseudobinary compounds.

The ordinary Hall coefficient R0 has been obtained to get information about conduction state. R0 is positive and almost the same for all the compounds of GdAg1−xIn x. For La to Pr series accompanied by crystallographic transformation, R0 takes a maximum aroundx = 0.2 and decreases to negative with increasing x for x > 0.2.

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.

We present experimental results on thermopower ( S ) and electrical resistivity ( ϱ ) of Y(Al x Co 1- x ) 2 compounds, with 0 ⩽ x ⩽ 0.15. The properties were measured in the temperature range from 2 up to 300 K, in the longitudinal magnetic field ( H ) from 0 to 15 T. These are the first measurements of thermopower for these alloys (for x > 0). Our results show that with increasing Al content the Co 3d peak in density of states narrows. This narrowing occurs mainly due to increasing localisation of Co 3d electrons caused by the disorder within Co sublattice. At low temperatures the scattering by spin fluctuations dominates the transport properties of the compounds with x ϱ/ϱ = ( ϱ ( T, H ) - ϱ ( T , 0))/ ϱ ( T , 0) is positive. The magnetothermopower Δ S = S ( H ) - S (0) reveals a maximum at almost the same temperature as the minimum of S (0), at this temperature Δ S ≈} H 2 . Δ S decreases with Al content as does S (0), whereas the impurity contribution to the resistivity dramatically increases. At x > 0.01, a large positive maximum develops in the thermopower instead of the minimum and Δ S vanishes.

Temperature dependencies of thermopower S ( T ) of Fe 2 P compound with hexagonal structure have been measured between 2 and 300 K in magnetic fields up to 15 T. S ( T ) takes a minimum around 20 K and shows a kink at T c . T c has a large magnetic field H dependence. The S ( T ) curve after cooling from room temperature to 2 K in magnetic field of 15 T reveals two characteristic features, the shoulder between 60 and 70 K and the discontinuity at T c .

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.