60 research outputs found
Half-metallic ferromagnetism with high magnetic moment and high Curie temperature in CoFeSi
CoFeSi crystallizes in the ordered L2 structure as proved by X-ray
diffraction and M\"o\ss bauer spectroscopy. The magnetic moment of CoFeSi
was measured to be about at 5K. Magnetic circular dichroism spectra
excited by soft X-rays (XMCD) were taken to determine the element specific
magnetic moments of Co and Fe. The Curie temperature was measured with
different methods to be ()K. CoFeSi was found to be the Heusler
compound as well as the half-metallic ferromagnet with the highest magnetic
moment and Curie temperature.Comment: conference contribution, MMM200
Interplay between Superconductivity and Magnetism in Rb0.8Fe1.6Se2 under Pressure
High-pressure magnetization, structural and 57Fe M\"ossbauer studies were
performed on superconducting Rb0.8Fe1.6Se2.0 with Tc = 32.4 K. The
superconducting transition temperature gradually decreases on increasing
pressure up to 5.0 GPa followed by a marked step-like suppression of
superconductivity near 6 GPa. No structural phase transition in the Fe
vacancy-ordered superstructure is observed in synchrotron XRD studies up to
15.6 GPa, while the M\"ossbauer spectra above 5 GPa reveal the appearance of a
new paramagnetic phase and significant changes in the magnetic and electronic
properties of the dominant antiferromagnetic phase, coinciding with the
disappearance of superconductivity. These findings underline the strong
correlation between antiferromagnetic order and superconductivity in
phase-separated AxFe2-x/2Se2 (A = K, Rb, Cs) superconductors
Intercalation effect on hyperfine parameters of Fe in FeSe superconductor with Tc = 42 K
57Fe-Mossbauer spectra of superconducting beta-FeSe, the Li/NH3 intercalate
product and a subsequent sample of this intercalate treated with moist He gas
have been measured in temperature range 4.7 - 290 K. A correlation is
established between hyperfine parameters and critical temperature Tc in these
phases. A strong increase of isomer shift upon intercalation is explained by a
charge transfer from the Li/NH3 intercalate to the FeSe layers resulting in an
increase of Tc up to 42 K. A significant decrease of the quadrupole splitting
above 240 K has been attributed to diffusive motion of Li+ ions within the
interlamellar space.Comment: 6 pages, 5 figures, 1 tabl
Electronic structure, magnetism, and disorder in the Heusler compound CoTiSn
Polycrystalline samples of the half-metallic ferromagnet Heusler compound
CoTiSn have been prepared and studied using bulk techniques (X-ray
diffraction and magnetization) as well as local probes (Sn M\"ossbauer
spectroscopy and Co nuclear magnetic resonance spectroscopy) in order to
determine how disorder affects half-metallic behavior and also, to establish
the joint use of M\"ossbauer and NMR spectroscopies as a quantitative probe of
local ion ordering in these compounds. Additionally, density functional
electronic structure calculations on ordered and partially disordered
CoTiSn compounds have been carried out at a number of different levels of
theory in order to simultaneously understand how the particular choice of DFT
scheme as well as disorder affect the computed magnetization. Our studies
suggest that a sample which seems well-ordered by X-ray diffraction and
magnetization measurements can possess up to 10% of antisite (Co/Ti)
disordering. Computations similarly suggest that even 12.5% antisite Co/Ti
disorder does not destroy the half-metallic character of this material.
However, the use of an appropriate level of non-local DFT is crucial.Comment: 11 pages and 5 figure
Geometric, electronic, and magnetic structure of CoFeSi: Curie temperature and magnetic moment measurements and calculations
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 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, CoFeSi was
revisited. The compound was investigated in detail concerning its geometrical
and magnetic structure by means of X-ray diffraction, X-ray absorption and
M\"o\ss bauer spectroscopies as well as high and low temperature magnetometry.
The measurements revealed that it is, currently, the material with the highest
magnetic moment () and Curie-temperature (1100K) in the classes of
Heusler compounds as well as half-metallic ferromagnets. The experimental
findings are supported by detailed electronic structure calculations
Proton-Coupled Electron Transfer in Ferrocenium–Phenolate Radicals
Electron
and proton transfer (ET, PT) can be intimately coupled,
provided suitable redox and acid/base sites are available. The amide-linked
ferrocene–phenol <b>H-1</b> is deprotonated to the phenolate <b>[1]</b><sup><b>–</b></sup> by phosphazene bases and
oxidized to the ferrocenium ion <b>[H-1]</b><sup><b>+</b></sup> by silver hexafluoroantimonate. Concomitant oxidation and
deprotonation yields the radical <b>[1]</b><sup><b>•</b></sup>, featuring a characteristic near-IR absorption band. The ground
state of <b>[1]</b><sup><b>•</b></sup> is best
described as the ferrocenium–phenolate zwitterion <b>[1b]</b><sup><b>•</b></sup> with a dynamic dissymmetric N···H···O
hydrogen bond (PT). The ferrocenium–iminolate N···H–O
tautomer <b>[1b]</b><sup><b>•</b></sup><b>-NHO′</b> can undergo a thermal structural rearrangement to the high-energy
OH···O tautomer <b>[1b]</b><sup><b>•</b></sup><b>-OHO</b>, while the amide–phenolate N–H···O
tautomer <b>[1b]</b><sup><b>•</b></sup><b>-NHO</b> is poised to optical electron transfer to yield the ferrocene–phenoxyl
valence isomer <b>[1a]</b><sup><b>•</b></sup><b>-NHO</b> (<i>E</i><sub>op</sub> = 1.18–1.19 eV)
Synthesis of Nanocrystals and Particle Size Effects Studies on the Thermally Induced Spin Transition of the Model Spin Crossover Compound [Fe(phen) 2 (NCS) 2 ]
International audienc
- …