Half-Metallic Ferromagnetism in the Heusler Compound Co2_2FeSi revealed by Resistivity, Magnetoresistance, and Anomalous Hall Effect measurements

We present electrical transport data for single-crystalline Co$_2$FeSi which provide clear-cut evidence that this Heusler compound is truly a half-metallic ferromagnet, i.e. it possesses perfect spin-polarization. More specifically, the temperature dependence of $\rho$ is governed by electron scattering off magnons which are thermally excited over a sizeable gap $\Delta\approx 100 K$ ($\sim 9 meV$) separating the electronic majority states at the Fermi level from the unoccupied minority states. As a consequence, electron-magnon scattering is only relevant at $T\gtrsim\Delta$ but freezes out at lower temperatures, i.e., the spin-polarization of the electrons at the Fermi level remains practically perfect for $T\lesssim\Delta$. The gapped magnon population has a decisive influence on the magnetoresistance and the anomalous Hall effect (AHE): i) The magnetoresistance changes its sign at $T\sim 100 K$, ii) the anomalous Hall coefficient is strongly temperature dependent at $T\gtrsim 100 K$ and compatible with Berry phase related and/or side-jump electronic deflection, whereas it is practically temperature-independent at lower temperatures

Crystal growth and electronic phase diagram of 4d doped Na1 delta Fe1 xRhxAs in comparison to 3d doped Na1 delta Fe1 xCoxAs

Single crystals of Na1 amp; 8722; amp; 948;Fe1 amp; 8722;xTxAs with T Co, Rh have been grown using a self flux technique. The crystals were thoroughly characterized by powder x ray diffraction, magnetic susceptibility, and electronic transport with particular focus on the Rh doped samples. Measurements of the specific heat and ARPES were conducted exemplarily for the optimally doped compositions. The spin density wave transition SDW observed for samples with low Rh concentration 0 amp; 8804;x amp; 8804;0.013 is fully suppressed in the optimally doped sample. The superconducting transition temperature Tc is enhanced from 10 K in Na1 amp; 8722; amp; 948;FeAs to 21 K in the optimally doped sample x 0.019 of the Na1 amp; 8722; amp; 948;Fe1 amp; 8722;xRhxAs series and decreases for the overdoped compounds, revealing a typical shape for the superconducting part of the electronic phase diagram. Remarkably, the phase diagram is almost identical to that of Co doped Na1 amp; 8722; amp; 948;FeAs, suggesting a generic phase diagram for both dopant