First-principles electronic structure of spinelLiCr2O4:A possible half-metal

2004

We have employed first-principles electronic structure calculations to examine the hypothetical (but plausible) oxide spinel, ${\mathrm{LiCr}}_{2}{\mathrm{O}}_{4}$ with the ${d}^{2.5}$ electronic configuration. The cell (cubic) and internal (oxygen position) structural parameters have been obtained for this compound through structural relaxation in the first-principles framework. Within the one-electron band picture, we find that ${\mathrm{LiCr}}_{2}{\mathrm{O}}_{4}$ is magnetic, and a candidate half-metal. The electronic structure is substantially different from the closely related and well-known rutile half-metal ${\mathrm{CrO}}_{2}.$ In particular, we find a smaller conduction-band width…

Properties of the quaternary half-metal-type Heusler alloyCo2Mn1−xFexSi

2006

This paper reports on the bulk properties of the quaternary Heusler alloy Co2Mn1�xFexSi with the Fe concentration x =0,1/2,1. All samples, which were prepared by arc melting, exhibit L21 long-range order over the complete range of Fe concentration. The structural and magnetic properties of the Co2Mn1�xFexSi Heusler alloys were investigated by means of x-ray diffraction, high- and low-temperature magnetometry, Mossbauer spectroscopy, and differential scanning calorimetry. The electronic structure was explored by means of highenergy photoemission spectroscopy at about 8 keV photon energy. This ensures true bulk sensitivity of the measurements. The magnetization of the Fe-doped Heusler alloys …

Verwey-type transition in EuNiP

2006

High temperature 151Eu Mossbauer measurements provide proof for inhomogeneous mixed-valent behaviour in EuNiP. We observed that EuNiP undergoes a Verwey-type charge delocalisation transition when heated above 470 K prior to the structural γ-β phase transition at T ≈ 510 K. This finding confirms the results of photoemission spectroscopy in the isostructural compound EuPdP and of TB-LMTO-ASA band structure calculations. We discuss the role of a van Hove singularity associated with a high density of 4f states close to the Fermi energy in inhomogeneous mixed europium valency, and the microscopic mechanism of γ-β phase transition in compounds analogous to EuNiP.

Covalent bonding and the nature of band gaps in some half-Heusler compounds

2005

Half-Heusler compounds \textit{XYZ}, also called semi-Heusler compounds, crystallize in the MgAgAs structure, in the space group $F\bar43m$. We report a systematic examination of band gaps and the nature (covalent or ionic) of bonding in semiconducting 8- and 18- electron half-Heusler compounds through first-principles density functional calculations. We find the most appropriate description of these compounds from the viewpoint of electronic structures is one of a \textit{YZ} zinc blende lattice stuffed by the \textit{X} ion. Simple valence rules are obeyed for bonding in the 8-electron compound. For example, LiMgN can be written Li$^+$ + (MgN)$^-$, and (MgN)$^-$, which is isoelectronic wi…

The half-metallic ferromagnet

2007

Abstract Electronic structure calculation were used to predict a new material for spintronic applications. Co 2 Mn 0.5 Fe 0.5 Si is one example which is stable against on-site correlation and disorder effects due to the position of the Fermi energy in the middle of the minority band gap. Experimentally the sample were made exhibiting L 2 1 structure and a high magnetic order.

Slater-Pauling Rule and Curie-Temperature of Co$_2$-based Heusler compounds

2005

A concept is presented serving to guide in the search for new materials with high spin polarization. It is shown that the magnetic moment of half-metallic ferromagnets can be calculated from the generalized Slater-Pauling rule. Further, it was found empirically that the Curie temperature of Co$_2$ based Heusler compounds can be estimated from a seemingly linear dependence on the magnetic moment. As a successful application of these simple rules, it was found that Co$_2$FeSi is, actually, the half-metallic ferromagnet exhibiting the highest magnetic moment and the highest Curie temperature measured for a Heusler compound.

Structure and Properties of GdAuSn and the GdAuSn/MnAuSn System

2006

The crystal structure of GdAuSn was refined by means of single crystal X-ray diffraction. Band structure calculations based on the structural data confirmed the antiferromagnetic ground state and the metallic behaviour of GdAuSn. 119mSn, 155Gd and 197Au Mossbauer spectroscopic studies were used to verify the values of the hyperfine parameters that were given by the band structure calculations. Band structure calculations of MnAuSn confirmed that this half-Heusler compound belongs to the family of half-metallic ferromagnets. Magnetic susceptibility, conductivity and Mossbauer studies were used to characterize granular material based on the half-Heusler ferromagnet MnAuSn in the antiferromagn…

Crystal Structures of Ln2Pd2Pb (Ln: Y, La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, and Lu) Compounds.

2004

Investigation of Co$_2$FeSi: The Heusler compound with Highest Curie Temperature and Magnetic Moment

2006

This work reports on structural and magnetic investigations of the Heusler compound Co$_2$FeSi. X-Ray diffraction and M\"o\ss bauer spectrometry indicate an ordered $L2_1$ 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 ($6 \mu_B$) and Curie-temperature (1100K) in the classes of Heusler compounds as well as half-metallic ferromagnets.

Correlation in Heusler compounds YSi(Y=3d transition metal)

2007

Abstract Ferromagnetic Co 2 -based Heusler compounds have generated increasing interest over the last few years because of their peculiar electronic structure. They exhibit a band gap for the electrons of one direction and are metallic for the other. Further, they cover a very wide range of magnetic moments and Curie temperatures. Despite lot of efforts in theory and experiment to describe bulk materials and thin films, there are some marked discrepancies between observed and predicted properties of these materials. These discrepancies appear not only across but also within synthesis methods as well as in the theoretical predictions. In this contribution, the electronic structure of Co 2 YS…

Charakterisierung von dotierten Heusler-Verbindungen: Co2Cr1−xFexAl

2004

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…

Correlation in the transition-metal-based Heusler compoundsCo2MnSiandCo2FeSi

2006

Half-metallic ferromagnets, such as the Heusler compounds with formula ${X}_{2}YZ$, are expected to show an integer value for the spin magnetic moment. In contrast to experiments, calculations give noninteger values in certain cases where the compounds are based on $X=\mathrm{Co}$. In order to explain deviations of the magnetic moment calculated for such compounds, the dependence of the electronic structure on the lattice parameter was studied theoretically. In the local density approximation (LDA), the minimum total energy of ${\mathrm{Co}}_{2}\mathrm{FeSi}$ is found for the experimental lattice parameter, but the calculated magnetic moment is approximately 12% too low. In addition, half-m…

Geometric, electronic, and magnetic structure of Co$_2$FeSi: Curie temperature and magnetic moment measurements and calculations

2005

In this work a simple concept was used for a systematic search for new materials with high spin polarization. It is based on two semi-empirical models. Firstly, 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 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, Co$_2$FeSi was revisited. The compound was investigated in detail concerning its geometrical and magnetic structure by m…