Ch. Kleeberg

The thermoelectric power of ferromagnetically ordered Cu1−xGaxCr2Se4 spinels

Abstract The absolute thermoelectric power and the electrical resistivity of Cu 1− x Ga x Cr 2 Se 4 spinel single crystals have been measured in 〈0 0 1〉 direction and in the temperature range from 5 to 400 K and for compositions between x = 0.036 and x = 0.394. The above investigations showed that all compounds under study are p-type metallic conductors. It was also observed that the thermoelectric power can be explained considering only the diffusion component (which varies linearly with temperature) and a magnon drag contribution. The positive slope of the linear part of thermopower decreases with decreasing Ga concentration. The thermoelectric power of the sample with x = 0.036 does not depent on temperature for T > 200 K. These effects are explained in terms of spin- and alloy-scattering processes including non-stoichiometry.

Field- and anisotropy-induced states in MnAs1 − xPx-single crystals

Abstract Field-induced transitions have been observed earlier in manganese monopnictide polycrystals. However, the role played by anisotropy in these second order transitions remained unclear. In this contribution we present magnetization data for 4.2 K 0.83 P 0.17 and MnAs 0.88 P 0.12 single crystals and a clamped state of MnAs 0.97 P 0.03 . An attempt is made to describe these new combined anisotropy- and field-related states.

Thermal expansion of Mn2−xCrxSb single crystals

Abstract The thermal expansion Δ l / l has been measured and the thermal expansion coefficient α determined as a function of temperature and in the crystalline a - and c -directions of three Mn 2− x Cr x Sb single crystals, x =0.10, 0.05, 0.03. In both lattice directions α is different in the antiferromagnetic (afm) and ferrimagnetic (fi) phases (for example, x =0.03: α a =2.5×10 −5 K −1 ; T ≤ T s , α a =5×10 −5 K −1 ; T ≥ T s ), suggesting that the first-order afm–fi phase transition ( T s ) in these crystals should be described as a triggered coupled spin–lattice phase transition rather than as driven by lattice entropy.

Coherent ferromagnetic precipitation in Mn2−xCrxSb single crystals

Abstract A hexagonal ferromagnetic monopnictide, Mn1.07Cr0.11Sb, precipitates coherently along the (101)-planes of tetragonal Mn2−x Cr x Sb single crystals, acts as a nucleation site for the antiferromagmetic/ferrimagnetic transition of the bipnictide and introduces a quasifourfold anisotropy in the tetragonal plane.

Anisotropic magnetization of some ferromagnetic and canted transition metal pnictides

Abstract The anisotropic magnetization of some CrxMn1−xSb and MnAs1−yPy single crystals has been measured for temperatures 10 K

Field Dependent Specific Heat Capacity of Mn2—xCrxSb Single Crystals

The specific heat capacity versus temperature (80 K < T < 350 K) curves of three Mn 2-x Cr x Sb single crystals (x = 0.10, 0.05, 0.03) have been measured at different magnetic fields (0 < B < 13 T) and along the crystal directions a, c of the tetragonal lattice. Values of the entropy steps ΔS are reported as well as the magnetic field shifts of T s along the tetragonal crystal directions. The data are correlated in terms of the TPT model. Frozen-in spin entropy contributions are observed also and are related to interfacial strains which arise along the boundaries of the matrix and the ferromagnetic hexagonal secondary phase Mn 1.07 Cr 0.11 Sb, which precipitates along the [101] planes of the tetragonal matrix.

The Thermoelectric Power of Some Magnetically Ordered Transition Metal Pnictides

The thermoelectric power (TEP) S of MnAs 1-x P x (0 < x < 0.17) and Mn 2-y Cr y Sb (0 < y < 0.20) single crystals has been measured in the temperature range 77 K< T < 350 K and for various crystal orientations. For both the mono- and bipnictides, below the magnetic ordering temperatures T c or T N , the magnon contribution is dominant. In general, the magnetic order-order transitions can be detected in S(T) and values of the Fermi energy are obtained from the diffusion thermopower contribution Sd, once it is separated: for example EF (x = 0.17) = 3.85 eV, E F (y = 0.04) = 3.15 eV.