We present a detail study of the electrical resistivity, thermoelectric power, magnetic susceptibility c{hi} and the heat capacity CP in antiferromagnetic layered compounds CuCrS2 and CuCrSe2 at 2K-300K. CuCrS2 showed sharp cusp in c{hi} and a lambda
-like peak in CP at TN = 40K as expected for a 3D- magnetic order, while more metallic CuCrSe2 showed a rounded maximum in c{hi} and the absence of sharp peak in CP around 55K, the CP at low temperature has T2-dependence in it which suggests the absence of the long range order and 2D spin-liquid like excitation in its magnetic phase. We explain the absence of the magnetic order in the selenide compound as resulting from the effective competition of the magnetic interactions from the distant neighbors; the indirect exchange among the intra-layer Cr-atoms increases in more metallic selenide compound which competes with the direct antiferromagnetic interactions between the Cr-atoms of different layers which destroys the long range magnetic order.
The electrical, thermal conductivity and Seebeck coefficient of the quenched, annealed and slowly cooled phases of the layer compound CuCrS2 have been reported between 15K to 300K. We also confirm the antiferromagnetic transition at 40K in them by ou
r magnetic measurements between 2K and 300K. The crystal flakes show a minimum around 100K in their in-plane resistance behavior. For the polycrystalline pellets the resistivity depends on their flaky texture and it attains at most 10 to 20 times of the room temperature value at the lowest temperature of measurement. The temperature dependence is complex and no definite activation energy of electronic conduction can be discerned. We find that the Seebeck coefficient is between 200-450 microV/K and is unusually large for the observed resistivity values of between 5-100 mOhm-cm at room temperature. The figure of merit ZT for the thermoelectric application is 2.3 for our quenched phases, which is much larger than 1 for useful materials. The thermal conductivity K is mostly due to lattice conduction and is reduced by the disorder in Cu- occupancy in our quenched phase. A dramatic reduction of electrical and thermal conductivity is found as the antiferromagnetic transition is approached from the paramagnetic region, and K subsequently rises in the ordered phase. We discuss the transport properties as being similar to a doped Kondo-insulator.
Electrical conductivity, thermopower and magnetic properties of Fe-intercalated Fe0.33VSe2 has been reported between 4.2K - 300K. We observe a first order transition in the resistivity of the sintered pellets around 160K on cooling. The electronic pr
operties including the transitional hysteresis in the resistance anomaly (from 80K-160K) are found to be very sensitive to the structural details of the samples, which were prepared in different annealing conditions. The thermopower results on the sintered pellets are reported between 10K - 300K. The magnetic measurements between 2K - 300K and up to 14 Tesla field show the absence of any magnetic ordering in Fe0.33VSe2. The magnetic moment per Fe -atom at room temperature (between 1.4 to 1.7 Bohr Magneton) is much lower than in previously reported anti-ferromagnetic FeV2Se4. Furthermore, the Curie constant shows a rapid and continuous reduction and combined with the high field magnetization result at 2K suggests a rapid decrease in the paramagnetic moments on cooling to low temperatures and the absence of any magnetic order in Fe0.33VSe2 at low temperatures.
We present the results of the magnetic and specific heat measurements on V4 tetrahedral-cluster compound GaV4S8 between 2 to 300K. We find two transitions related to a structural change at 42K followed by ferromagnetic order at 12K on cooling. Remark
ably similar properties were previously reported for the cluster compounds of Mo4. These compounds show an extremely high density of low energy excitations in their electronic properties. We explain this behavior in a cluster compound as due to the reduction of coulomb repulsion among electrons that occupy highly degenerate orbits of different clusters.
