Search results for "Curie"
showing 10 items of 110 documents
Anomalous transport properties of the half-metallic ferromagnets Co 2 TiSi, Co 2 TiGe and Co 2 TiSn
2011
In this work the theoretical and experimental investigations of Co2TiZ (Z = Si, Ge, or Sn) compounds are reported. Half-metallic ferromagnetism is predicted for all three compounds with only two bands crossing the Fermi energy in the majority channel. The magnetic moments fulfill the Slater-Pauling rule and the Curie temperatures are well above room temperature. All compounds show a metallic like resistivity for low temperatures up to their Curie temperature, above the resistivity changes to semiconducting like behavior. A large negative magnetoresistance of 55% is observed for Co2TiSn at room temperature in an applied magnetic field of 4T which is comparable to the large negative magnetore…
Seebeck coefficients of half-metallic ferromagnets
2009
In this report the Co2 based Heusler compounds are discussed as potential materials for spin voltage generation. The compounds were synthesized by arcmelting and consequent annealing. Band structure calculations were performed and revealed the compounds to be half-metallic ferromagnets. Magnetometry was performed on the samples and the Curie temperatures and the magnetic moments were determined. The Seebeck coefficients were measured from low to ambient temperatures for all compounds. For selected compounds high temperature measurements up to 900 K were performed.
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.
Structural and Magnetic Properties of Co-Fe Binary Alloy Monolayers on W(110)
2003
We present an experimental investigation of ${\mathrm{C}\mathrm{o}}_{x}{\mathrm{F}\mathrm{e}}_{1\ensuremath{-}x}$ monolayers grown on flat and stepped W(110) surfaces. Atomically resolved scanning tunneling microscopy and low energy electron diffraction reveal continuous miscibility and pseudomorphic growth of Co and Fe for $0\ensuremath{\le}xl0.6$. We observe short range ordered ${\mathrm{C}\mathrm{o}\mathrm{F}\mathrm{e}}_{3}$-$p(2\ifmmode\times\else\texttimes\fi{}2)$ and CoFe-$c(2\ifmmode\times\else\texttimes\fi{}2)$ structures in the pseudomorphic monolayer. High Co concentrations lead to a phase separation. The Curie temperature and the ferromagnetic Kerr signal at low temperatures decr…
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…
Spin-polarized Low Energy Electron Diffraction
2007
We review recent progress in the understanding of the physics of ultrathin ferromagnetic films and surfaces that has been made using elastic spin-polarized low-energy electron diffraction (SPLEED). Further development of the experimental technique including high efficient electron sources, spin manipulation and imaging allows a wide range of applications. We report on a quantitative comparison of relativistic dynamical scattering calculations with SPLEED experiments on Fe(110) surfaces and Fe(100)/W(100) thin films leading to an understanding of the spatial distribution of spin densities. Exploiting the surface sensitivity in combination with the large asymmetry of SPLEED, it becomes feasib…
Epitaxy and magnetotransport ofSr2FeMoO6thin films
2000
By pulsed-laser deposition epitaxial thin films of ${\mathrm{Sr}}_{2}{\mathrm{FeMoO}}_{6}$ have been prepared on (100) ${\mathrm{SrTiO}}_{3}$ substrates. Already for a deposition temperature of 320 \ifmmode^\circ\else\textdegree\fi{}C epitaxial growth is achieved. Depending on deposition parameters the films show metallic or semiconducting behavior. At high (low) deposition temperature the FeMo sublattice has a rock-salt (random) structure. The metallic samples have a large negative magnetoresistance which peaks at the Curie temperature. The magnetic moment was determined to $4{\ensuremath{\mu}}_{B}$ per formula unit (f.u.), in agreement with the expected value for an ideal ferrimagnetic ar…
Electrical transport with temperature-induced spin disorder in NiMnSb
2019
Abstract We investigate theoretically the combined effect of phonons and magnons caused by finite temperatures on the electrical resistivity of nonstoichiometric half-Heusler NiMnSb alloy. The coherent potential approximation within the alloy analogy model is employed for an efficient treatment of chemical impurities, atomic displacements, and magnetic disorder. Spin fluctuations of local Mn moments are described by two models: (i) uncompensated disordered local moment approach and (ii) tilting of the moments. The calculated resistivity agrees with experimental data, the agreement is good up to 600 K. We show that a strong magnetic disorder leads to a violation of the Matthiessen’s rule for…
New Heusler Compounds and Their Properties
2013
Spintronics is a multidisciplinary field and a new research area. New materials must be found for satisfying the different types of requirement. 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.
Challenging the Prediction of Anionogenic Ferromagnetism for Rb4O6
2007
It has been suggested that Rb4O6 should be a half-metallic ferromagnet with the magnetic moment carried by the hyperoxide anions and a Curie temperature above room temperature. In the present work,...