In this work a simple concept was used for a systematic search for materials with high spin polarization. It is based on two semiempirical models. First, the Slater-Pauling rule was used for estimation of the magnetic moment. This model is well supported by electronic structure calculations. The second model was found particularly for ${\mathrm{Co}}_2$ based Heusler compounds when comparing their magnetic properties. It turned out that these compounds exhibit seemingly a linear dependence of the Curie temperature as function of the magnetic moment. Stimulated by these models, ${\mathrm{Co}}_2\mathrm{FeSi}$ was revisited. The compound was investigated in detail concerning its geometrical and magnetic structure by means of x-ray diffraction, x-ray absorption, and Mössbauer spectroscopies as well as high and low temperature magnetometry. The measurements revealed that it is, currently, the material with the highest magnetic moment $\left(6{\mu }_B\right)$ and Curie temperature (1100 K) in the classes of Heusler compounds as well as half-metallic ferromagnets. The experimental findings are supported by detailed electronic structure calculations.

Recent studies have reported an interesting class of semiconductor materials that bridge the gap between semiconductors and half-metallic ferromagnets. These materials, called spin gapless semiconductors, exhibit a band gap in one of the spin channels and a zero band gap in the other and thus allow for tunable spin transport. Here, we report the first experimental verification of the spin gapless magnetic semiconductor ${\mathrm{Mn}}_2\mathrm{CoAl}$, an inverse Heusler compound with a Curie temperature of 720 K and a magnetic moment of $2{\mu }_B$. Below 300 K, the compound exhibits nearly temperature-independent conductivity, very low, temperature-independent carrier concentration, and a vanishing Seebeck coefficient. The anomalous Hall effect is comparatively low, which is explained by the symmetry properties of the Berry curvature. ${\mathrm{Mn}}_2\mathrm{CoAl}$ is not only suitable material for room temperature semiconductor spintronics, the robust spin polarization of the spin gapless semiconductors makes it very promising material for spintronics in general.

This work reports on structural and magnetic investigations of the Heusler compound Co2FeSi. X-ray diffraction and Mößbauer spectrometry indicate an ordered L21 structure. Magnetic measurements by means of x-ray magnetic circular dichroism and magnetometry revealed that this compound is, currently, the material with the highest magnetic moment (6μB) and Curie temperature (1100K) in the classes of Heusler compounds as well as half-metallic ferromagnets.

This work reports about the electronic, magnetic, and structural properties of the binary compound Mn3Ga. The tetragonal DO22 phase of Mn3Ga was successfully synthesized and investigated. It has been found that the material is hard magnetic with an energy product of Hc×Br=52.5kJm−3 and an average saturation magnetization of about 0.25μB∕at. at 5K. The saturation magnetization indicates a ferrimagnetic order with partially compensating moments at the Mn atoms on crystallographically different sites. The Curie temperature is above 730K where the onset of decomposition is observed. The electronic structure calculations indicate a nearly half-metallic ferrimagnetic order with 88% spin polarization at the Fermi energy.

The Curie temperatures for the Heusler compounds ${\mathrm{Co}}_2\mathrm{Ti}\mathrm{Al}$, ${\mathrm{Co}}_2\mathrm{V}\mathrm{Ga}$, ${\mathrm{Co}}_2\mathrm{V}\mathrm{Sn}$, ${\mathrm{Co}}_2\mathrm{Cr}\mathrm{Ga}$, ${\mathrm{Co}}_2\mathrm{Cr}\mathrm{Al}$, ${\mathrm{Co}}_2\mathrm{Mn}\mathrm{Al}$, ${\mathrm{Co}}_2\mathrm{Mn}\mathrm{Sn}$, ${\mathrm{Co}}_2\mathrm{Mn}\mathrm{Si}$, and ${\mathrm{Co}}_2\mathrm{Fe}\mathrm{Si}$ are determined ab initio from the electronic structure obtained with the local-density functional approximation and/or the generalized gradient approximation. Frozen spin spirals are used to model the excited states needed to evaluate the spherical approximation for the Curie temperature. The spherical approximation is found to describe the experimental Curie temperatures very well which, for the compounds selected, extend over the range from $95\text{to}1100\mathrm{K}$; as a function of the valence electron count, they show an approximately linear trend which finds an explanation by our calculations.

This paper reports on the bulk properties of the quaternary Heusler alloy ${\mathrm{Co}}_2{\mathrm{Mn}}_{1-x}{\mathrm{Fe}}_x\mathrm{Si}$ with the Fe concentration $x=0,1∕2,1$. All samples, which were prepared by arc melting, exhibit $L{2}_1$ long-range order over the complete range of Fe concentration. The structural and magnetic properties of the ${\mathrm{Co}}_2{\mathrm{Mn}}_{1-x}{\mathrm{Fe}}_x\mathrm{Si}$ Heusler alloys were investigated by means of x-ray diffraction, high- and low-temperature magnetometry, Mössbauer spectroscopy, and differential scanning calorimetry. The electronic structure was explored by means of high-energy photoemission spectroscopy at about $8\mathrm{keV}$ photon energy. This ensures true bulk sensitivity of the measurements. The magnetization of the Fe-doped Heusler alloys is in agreement with the values of the magnetic moments expected for a Slater-Pauling-like behavior of half-metallic ferromagnets. The experimental findings are discussed on the basis of self-consistent calculations of the electronic and magnetic structure. To achieve good agreement with experiment, the calculations indicate that on-site electron-electron correlation must be taken into account, even at low Fe concentration. The present investigation focuses on searching for the quaternary compound where the half-metallic behavior is stable against outside influences. Overall, the results suggest that the best candidate may be found at an iron concentration of about 50%.