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DC magnetization M ( T ) and electrical resistivity ρ ( T ) have been studied in the temperature range of 4–300 K for (Cr99V 1)95Fe5 and (Cr99V 1)75Fe25 alloys. A minimum is observed near T N in ρ ( T ) curve for (Cr99V 1)95Fe5, which indicates the spin-density wave (SDW) antiferromagnetic transition. The progressive opening up of the SDW antiferromagnetic energy gap can be well described by a temperature-dependent energy gap function as 2 Δ ∝ T N − T . A paramagnetic–ferromagnetic transition is confirmed near T C in M ( T ) curve for (Cr99V 1)75Fe25, but no anomaly is observed around T C in ρ ( T ) curve that would be covered up by magnetic cluster-dependent scattering. The analyses indicated the magnetic clusters start to form at relatively high temperature above the transition temperature. T N and the SDW antiferromagnetism are rapidly depressed for Fe-poor (Cr99V 1)95Fe5 while T C and the ferromagnetism are rapidly increased for Fe-rich (Cr99V 1)75Fe25 by the substitution of light doping V for Cr.

Lattice effects related to metal–insulator (M–I) and charge-ordered (CO) transitions have been studied through the thermal expansion and the thermal conductivity measurements from 77 to 450 K in La 0.7 Ca 0.3 Mn 0.9 Cr 0.1 O 3 and La 0.4 Ca 0.6 Mn 0.99 Cr 0.01 O 3 . Thermal-expansion coefficient shows an obvious contraction near the M–I transition temperature T MI , but a sharp increase around the CO transition temperature T CO . Thermal conductivity is enhanced below both T MI and T CO . These findings are attributed to the strong charge–lattice coupling associated with the different electron states in manganites.

The dc magnetization, the electrical resistivity and the thermal conductivity have been measured in the temperature range of 5–300 K for Cr 67 Fe 23 Mn 10 and Cr 55 Fe 25 Mn 20 alloys. Curie temperature was confirmed and the ferromagnetic phase is not long-range order; Neel temperature was recorded and the antiferromagnetic phase is of spin-density wave (SDW). Our results are discussed on the basis of the magnetic nesting associated with paramagnetic and ferromagnetic cluster and SDW antiferromagnetic in this system.

The thermal conductivity k ( T ) of R 0.7 A 0.3 Mn 1- x Cr x O 3 (R=La, Nd; A=Ca, Sr) have been studied as a function of Cr content ( x ) ranging from 0.01 to 0.60. The Cr 3+ ions substitution for Mn 3+ ions causes the orbital defect of electrons, resulting in the volume shrinkage of lattice. The light doping of Cr strongly suppresses the thermal conductivity k over a wide range of temperature. On the contrary, for the heavily Cr doping samples, a clear rebound in k was observed at the higher temperature region studied, which is not consistent with a typical impurity effect on lattice thermal conductivity. These findings are discussed on the basis of the lattice distortion associated with the local Jahn–Teller effect through orbital–lattice coupling, and as well the spin–dependent scattering through spin–lattice interactions

The thermal conductivity $\kappa (H,T)$ of the new superconductor $MgB_2$ was studied as a function of the temperature and a magnetic field. No anomaly in the thermal conductivity $\kappa (H,T)$ is observed around the superconducting transition in absence or presence of magnetic fields up to 14 Tesla; upon that field the superconductivity of $MgB_2$ persisted. The thermal conductivity in zero-field shows a $T$-linear increase up to 50K. The thermal conductivity is found to increase with increasing field at high fields. We interpret the findings as if there are two subsystems of quasiparticles with different field-dependent characters in a two ($L$ and $S$)-band superconductor reacting differently with the vortex structure. The unusual enhancement of $\kappa (H ,T)$ at low temperature but higher than a ($H_{c2S}\simeq 3T$) critical field is interpreted as a result of the overlap of the low energy states outside the vortex cores in the $S$-band.

The electrical resistivity, thermal conductivity and low-frequency internal friction of Cr 75 (Fe x Mn 1− x ) 25 ( x =0.64, 0.72) alloys are studied in the temperature range 77–300 K. The initial increase in the resistivity and the decrease in the thermal conductivity as temperature decreases below T N are attributed to the progressive opening of the energy gap related to the antiferromagnetic transition in the alloys. The energy gap is estimated and the lower limit of value 2Δ( T C )/ k B T C is 1.13 and 1.30 for Cr 75 (Fe x Mn 1− x ) 25 of x =0.64 and 0.72, respectively.

Publisher Summary This chapter investigates a thermal conductivity measuring system, including the measuring setup and corresponding control software, which was developed to measure the thermal conductivity of rod samples with millimeter scale in temperature range 4.2–300K. The method of longitudinal steady thermal flow is used in the measurement. In this simplest steady-state experimental arrangement, heat is supplied at one end of a rod of uniform cross-sectional area A at a known rate Q and is removed at the other end. Vacuum of the sample chamber was kept 10-4 Pa during the measurement. The temperature difference on the sample generated by the gradient heater is monitored directly with a differential thermocouple. The temperature difference on the sample is controlled about 1 K. The precisions and applicability are proved by experiments on a number of materials including superconductors, SDW alloys, CMR materials, as well as engineering materials.

Direct current resistivity and its temperature dependence for nanostructured NiAl (n‐NiAl) was investigated at temperatures from 77 to 300 K. The resistivity of n‐NiAl (size 5–6 nm) was higher than that of polycrystalline NiAl and increased with decreasing density. For the n‐NiAl with relative density D≳70%, the resistivity decreased with decreasing temperature, manifesting metallic behavior. However, its temperature coefficient of resistivity decreased monotonically with decreasing density, and changed sign from positive to negative at densities 68%–70%, below which it displays on nonmetallic behavior. These results can be well interpreted by dominant grain boundary scattering.