J.-W. Schünemann

Specific heat capacity of mn1+δas1−xsbx single crystals

Abstract The specific heat capacity C p of Mn 1+δ As 1−x Sb x single crystals with 0≦ x ≦1, 0 at. % ≦ δ ≦ 2 at. % is presented for 110 K T x − T phase diagram and compared with those in the literature. From the analysis of C p ( T ) we find evidence for a transition from a ferromagnetic to a spin-glass-like state (at T u ) and only at T f > T u is paramagnetism attained. Temperatureinduced “in-layer randomization” of the manganese displacements might occur for mixed crystals with small x and for vacancy-disordered MnAs.

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.

The conductivity of MnAs1−xSbx and CryMn1−ySb single crystals

The temperature dependence of the resistivities of some MnAs1−xSbx and CryMn1−ySb single crystals and polycrystals have been measured for 4.2 K < T < 650 K and different crystal axes. While magnon scattering appears to be dominant for near-stoichiometric end-member crystals, for mixed or non-stoichiometric crystals a distinctly different behaviour occurs which we connect with the occurrence of particular phonon-magnon mixed modes which appear to be typical for crystals with a random component.

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

A martensitic-like transformation in MnAs?

Abstract Some experimental data on MnAs arc summarized in view of a recent reinterpretation of the phase transitions in that compound. Alternative models which are also compatible with the data are discussed.

Determination of carrier concentrations and mobilities in semi-metallic magnetic compounds

Abstract Recently, for a simultaneous and separate determination of n , p and the mobilities μ n , μ p of (intrinsic and doped) semiconductor samples and intercalation compounds a combination of time resolved thermoelectric power (TTE), conductivity and Hall-effect has been proposed. We attempt to apply this method to metallic magnetic compounds like MnAs 1− x P x Mn 1− x Sb or (Fe 1− x Mn x ) 2 P, because here the observed ferromagnetic coupling is likely to be determined by the number of ( n and/or p ) free carriers. For the correlation of the free carrier concentration and the fm Curie temperature, we have assembled a TTE-apparatus which has already been tested successfully using semiconductors. With semiconductors, the TTE-signal decomposes into three time regimes i.e. photogeneration (I), ambipolar diffusion (II) and thermoelectric effect (III).

Pressure derivatives of TC in amorphous (Fe100-xMnx)75P15C10 alloys

Abstract The effect of hydrostatic pressure on the temperature dependence of the permeability of amorphous (Fe 100- x Mn x ) 75 P 15 C 10 alloys with x =0, 20, 30 was measured up to 15 kbar. The Curie temperatures T C decrease, pressure at rates of dT C /dP = −2.3, −2.2, −1.9 K/kbar for x = 0, 20, and 30 at% Mn, respectively. The results are discussed in the framework of a cation mixing model. It is supposed that the exchange energy T MnMn increases and T FeMn decreases under pressure, thus resulting in the weak dependence of d T C /d P on manganese concentration.

Hall effect and resistivity of amorphous (Fe1-xVx)75P15C10 alloys

Abstract The resistivity and the Hall resistivity have been measured as functions of temperature and external magnetic field for (Fe 1- x V x ) 75 P 15 C 10 amorphous alloys up to 9% V and are discussed in terms of various possible scattering mechanisms. The magnetic behaviour could be described using a simplified version of the CPA-approximation. A correlation between the resistivity and its temperature derivative was observed but as a new result also the anomalous Hall constant and its temperature derivative are correlated.

Feromagnetism in NiAs-type CoFeTe

Abstract The magnetic behaviour of NiAs-type (Co 1− y Fe y ) 1− x Te ( x = 0.36) has been characterized by magnetization measurements at low temperatures (4.2–300 K). All samples investigated ( y = 0.3, 0.5, 0.7) were weakly ferromagnetic with a small magnetic moment of about 0.1 μ B per transition metal atom; within this series of alloys magnetic ordering occurred at 30 K, 40 K and 15 K respectively. A competitive character of the magnetic interactions seemed to be indicated.

CORRELATION OF TRANSPORT AND TOPOLOGICAL/SPIN DISORDER FOR SOME AMORPHOUS METALLIC AND MAGNETIC ALLOYS

The resistivity ρ and the permeability μ of amorphous magnetic ribbons (Fe100−xMnx)75P15C10 are determined at ambient pressure and pressures up to 15 kbar and correlated with the topological and magnetic disorder. The characterization includes the Curie temperature Tc, its pressure derivative ∂Tc/∂p and the pressure dependence of the resistivity minimum temperature.