Dirk Bombor

Half-metallic ferromagnetism with unexpectedly small spin splitting in the Heusler compound Co2FeSi.

We present electrical transport data for single-crystalline Co2FeSi which provide clear-cut evidence that this Heusler compound is truly a half-metallic ferromagnet, i.e. it possesses perfect spinpolarization. More specifically, the temperature dependence of ρ is governed by electron scattering off magnons which are thermally excited over a sizeable gap ∆ ≈ 100 K (∼ 9 meV) separating the electronic majority states at the Fermi level from the unoccupied minority states. As a consequence, electron-magnon scattering is only relevant at T & ∆ but freezes out at lower temperatures, i.e., the spin-polarization of the electrons at the Fermi level remains practically perfect for T . ∆. The gapped magnon population has a decisive influence on the magnetoresistance and the anomalous Hall effect (AHE): i) The magnetoresistance changes its sign at T ∼ 100 K, ii) the anomalous Hall coefficient is strongly temperature dependent at T & 100 K and compatible with Berry phase related and/or side-jump electronic deflection, whereas it is practically temperature-independent at lower temperatures.

Phase diagram of the iron arsenide superconductors Ca(Fe1−xCox)2As2(0⩽x⩽0.2)

Platelet-like single crystals of the Ca(Fe1-xCox)2As2 series having lateral dimensions up to 15 mm and thickness up to 0.5 mm were obtained from the high temperature solution growth technique using Sn flux. Upon Co doping, the c-axis of the tetragonal unit cell decreases, while the a-axis shows a less significant variation. Pristine CaFe2As2 shows a combined spin-density-wave and structural transition near T = 166 K which gradually shifts to lower temperatures and splits with increasing Co-doping. Both transitions terminate abruptly at a critical Co-concentration of xc = 0.075. For x \geq 0.05, superconductivity appears at low temperatures with a maximum transition temperature TC of around 20 K. The superconducting volume fraction increases with Co concentration up to x = 0.09 followed by a gradual decrease with further increase of the doping level. The electronic phase diagram of Ca(Fe1-xCox)2As2 (0 \leq x \leq 0.2) series is constructed from the magnetization and electric resistivity data. We show that the low-temperature superconducting properties of Co-doped CaFe2As2 differ considerably from those of BaFe2As2 reported previously. These differences seem to be related to the extreme pressure sensitivity of CaFe2As2 relative to its Ba counterpart.

Specific heat of Ca0.32Na0.68Fe2As2 single crystals: Unconventional s+/- multiband superconductivity with intermediate repulsive interband coupling and sizable attractive intraband couplings

We report a low-temperature specific heat study of high-quality single crystals of the heavily hole doped superconductor Ca

Hole doping in BaFe2As2: The case of Ba1-xNaxFe2As2 single crystals

_{0.32}

Transport and thermal properties of single- and polycrystalline NiZr0.5Hf0.5Sn

Na

Peculiarities of anisotropic electrical resistivity in Lu2PdSi3 single crystals

_{0.68}

Combined resistivity and Hall effect study on NaFe1−xRhxAs single crystals

Fe

Crystal growth and the electronic phase diagram of the 4

_2

d

As

doped Na

_2