Structure and properties of CoMnSb in the context of half-metallic ferromagnetism

2006

Although its X-ray powder diffraction patterns show a superstructure, the compound CoMnSb, like the well-known half-Heusler alloy NiMnSb, is often referred to the category of half-metallic ferromagnets with $C{1}_{b}$ structure. Our study assigns CoMnSb to space group $Fm\overline{3}m$. The crystal structure of CoMnSb can be represented as an alternation of ${\mathrm{Co}}_{2}\mathrm{Mn}\mathrm{Sb}$ and MnSb structural units, and, in contrast to NiMnSb, displays three Mn and two Sb positions in the elementary cell. The presence of nonequivalent antimony and manganese positions was verified using NMR and M\"ossbauer spectroscopic measurements. Band-structure calculations based on a proposed s…

Dünne epitaktische Filme der Heusler-Phase Co2Cr0,6Fe0,4Al

2004

Element-specific magnetic moments from core-absorption magnetic circular dichroism of the doped Heusler alloyCo2Cr0.6Fe0.4Al

2003

The magnetic circular dichroism (MCD) of core-level absorption (x-ray absorption spectroscopy, XAS) spectra in the soft x-ray region has been measured for the ferromagnetic Heusler alloy ${\mathrm{Co}}_{2}{\mathrm{Cr}}_{0.6}{\mathrm{Fe}}_{0.4}\mathrm{Al}$ at the Co, Fe, and Cr ${L}_{II,III}$ edges. The comparison of XAS spectra before and after in situ cleaning of polished surfaces revealed a pronounced selective oxidation of Cr in air. For clean surfaces we observed a MCD for all three elements with Fe showing the largest moment per atom. The MCD can be explained by the density of states of the $3d$ unoccupied states, predicted by linear muffin-tin orbital atomic sphere approximation. For …

Co2CrIn: A further magnetic Heusler compound

2006

Summary and Outlook In summary, this work presents the synthesis andcharacterisation of the Heusler compound Co 2 CrIn.The compound is L2 1 ordered and shows no major an-tisite disorder. Co 2 CrIn turns out to be a ferrimagnetwith a magnetic moment of 1.18 µ B at 5 K. In addi-tion, the hysterisis curve reveals a soft magnetic be-haviour. A measurement of the site specific magneticmomentsis highlydesirableas it might leadto a deeperunderstanding of the magnetic properties of Co 2 CrIn.Furthermore, the measured magnetic moment is not aninteger number, as expected for a half-metallic ferro-magnet. Thus, Co 2 CrIn can not be a half-metallic fer-romagnet, as most of the other Co 2 YZ Heusler com-…

Investigation of a novel material for magnetoelectronics: Co2Cr0.6Fe0.4Al

2003

Heusler compounds are promising candidates for future spintronics device applications. The electronic and magnetic properties of Co2Cr0.6Fe0.4Al, an electron-doped derivative of Co2CrAl, are investigated using circularly polarized synchrotron radiation and photoemission electron microscopy (PEEM). Element specific imaging reveals needle shaped Cr rich phases in a homogeneous bulk of the Heusler compound. The ferromagnetic domain structure is investigated on an element-resolved basis using x-ray magnetic circular dichroism (XMCD) contrast in PEEM. The structure is characterized by micrometre-size domains with a superimposed fine ripple structure; the lateral resolution in these images is abo…

Properties of Co/sub 2/YZ Heusler compounds

2005

Heusler compounds of Co/sub 2/XY composition (Co/sub 2/Cr/sub 0.6/Fe/sub 0.4/Al, Co/sub 2/FeSi) offer a variety of half-metallic ferromagnetic materials. These were prepared by arc melting and comprehensively characterized by means of X-ray diffraction ( XRD), Mossbauer spectroscopy, magnetic X-ray circular dichroism spectroscopy (MXCD), superconducting quantum interference device (SQUID) magnetometry, electron spectroscopy for chemical analysis (ESCA), extended X-ray absorption fine structure (EXAFS) and Auger electron spectroscopy (AES) depth profiling. Structural disorder phenomena, magnetic hysteresis, magnetic moments, magnetic transition temperatures and Curie temperature were obtaine…

On the half-metallicity of Co2FeSi Heusler alloy: Point-contact Andreev reflection spectroscopy andab initiostudy

2013

Co2FeSi, a Heusler alloy with the highest magnetic moment per unit cell and the highest Curie temperature, has largely been described theoretically as a half-metal. This conclusion, however, disagrees with point contact Andreev reflection (PCAR) spectroscopy measurements, which give much lower values of spin polarization, P. Here, we present the spin polarization measurements of Co2FeSi by the PCAR technique, along with a thorough computational exploration, within the DFT and a GGA+U approach, of the Coulomb exchange U parameters for Co and Fe atoms, taking into account spin-orbit coupling. We find that the orbital contribution (mo) to the total magnetic moment (mT) is significant, since it…

Co2CrIn: A Further Magnetic Heusler Compound

2006

Summary and Outlook In summary, this work presents the synthesis andcharacterisation of the Heusler compound Co 2 CrIn.The compound is L2 1 ordered and shows no major an-tisite disorder. Co 2 CrIn turns out to be a ferrimagnetwith a magnetic moment of 1.18 µ B at 5 K. In addi-tion, the hysterisis curve reveals a soft magnetic be-haviour. A measurement of the site specific magneticmomentsis highlydesirableas it might leadto a deeperunderstanding of the magnetic properties of Co 2 CrIn.Furthermore, the measured magnetic moment is not aninteger number, as expected for a half-metallic ferro-magnet. Thus, Co 2 CrIn can not be a half-metallic fer-romagnet, as most of the other Co 2 YZ Heusler com-…

Charakterisierung von dotierten Heusler-Verbindungen: Co2Cr1−xFexAl

2004

EXAFS-Messungen an dotierten Heusler-Verbindungen

2004

Magnetic properties of Co2Mn1−xFexSi Heusler alloys

2006

Co2Mn1−xFexSi Heusler alloys with Fe concentration x = 0–0.4 as prepared by arc melting show a L21 long range order for all Fe concentrations. Magnetic properties of Co2Mn1−xFexSi Heusler alloys were investigated by magnetometry and circular magnetic dichroism. The magnetization of the Fe doped Heusler alloys is in agreement with the Slater–Pauling values expected for half-metallic ferromagnets. Element specific magnetic moments as determined by x-ray absorption using the total electron yield method are in disagreement with theoretical predictions for x = 0 but approach the predicted values as the Fe concentration increases. Surprisingly small Fe concentration increases the magnetic moments…

Geometric, electronic, and magnetic structure ofCo2FeSi: Curie temperature and magnetic moment measurements and calculations

2005

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…

Rational design of new materials for spintronics: Co2FeZ (Z=Al, Ga, Si, Ge)

2008

Spintronic is a multidisciplinary field and a new research area. New materials must be found for satisfying the different types of demands. The search for stable half-metallic ferromagnets and ferromagnetic semiconductors with Curie temperatures higher than room temperature is still a challenge for solid state scientists. A general understanding of how structures are related to properties is a necessary prerequisite for material design. Computational simulations are an important tool for a rational design of new materials. The new developments in this new field are reported from the point of view of material scientists. The development of magnetic Heusler compounds specifically designed as …

Enhanced orbital magnetic moments in the Heusler compounds ,,

2004

Abstract Using the magnetic circular dichroism in X-ray absorption at the L2,3-edges of the 3d-transition metals, we determined the element specific ratio between orbital and spin magnetic moment of the Heusler compounds Co 2 CrAl , Co 2 Cr 0.6 Fe 0.4 Al and Co2FeAl. The orbital magnetic moment per spin is large (0.1–0.2) compared to bulk values of Fe and Co metals.

Structural properties of the quaternary Heusler compound Co2 Cr1−x Fex Al

2006

Abstract The structural and chemical properties of the quaternary Heusler compound Co2 Cr1−x Fex Al were investigated comparing powder and bulk samples. The long range order was determined by means of X-ray diffraction, while the site specific (short range) order was proved by the extended X-ray absorption fine structure method (EXAFS). The chemical composition was analysed by means of X-ray photo emission spectroscopy (XPS) combined with Auger electron spectroscopy (AES) depth profiling. The results from these methods are compared to get a detailed idea about the differences between surface and bulk properties and appearance of disorder in such alloys.

Epitaxial film growth and magnetic properties ofCo2FeSi

2006

We have grown thin films of the Heusler compound ${\mathrm{Co}}_{2}\mathrm{Fe}\mathrm{Si}$ by RF magnetron sputtering. On (100)-oriented MgO substrates we find fully epitaxial (100)-oriented and $L{2}_{1}$ ordered growth. On ${\mathrm{Al}}_{2}{\mathrm{O}}_{3}(11\overline{2}0)$ substrates, the film growth is (110)-oriented, and several in-plane epitaxial domains are observed. The temperature dependence of the electrical resistivity shows a power law with an exponent of $7∕2$ at low temperatures. Investigation of the bulk magnetic properties reveals an extrapolated saturation magnetization of $5.0{\ensuremath{\mu}}_{B}∕\mathrm{f.u.}$ at $0\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. The films on $…

Structural properties of the quaternary Heusler alloy Co2Cr1−xFexAl

2007

The quarternary substitutional series Co2Cr1?xFexAl was investigated by means of surface and bulk sensitive techniques in order to exploit its structural and compositional properties. Both bulk and powder samples of the alloy series were investigated to obtain specific information about this material.The long range order was determined by means of x-ray diffraction and neutron diffraction, while the site specific (short range) order was proved by extended x-ray absorption fine structure spectroscopy. The magnetic structure was investigated by M?ssbauer spectroscopy in transmission and scattering modes in order to compare and separate powder and bulk properties. The chemical composition was …