0000000000628186
AUTHOR
Christian G. F. Blum
Impact of local order and stoichiometry on the ultrafast magnetization dynamics of Heusler compounds
Nowadays, a wealth of information on ultrafast magnetization dynamics of thin ferromagnetic films exists in the literature. Information is, however, scarce on bulk single crystals, which may be especially important for the case of multi-sublattice systems. In Heusler compounds, representing prominent examples for such multi-sublattice systems, off-stoichiometry and degree of order can significantly change the magnetic properties of thin films, while bulk single crystals may be generally produced with a much more well-defined stoichiometry and a higher degree of ordering. A careful characterization of the local structure of thin films versus bulk single crystals combined with ultrafast demag…
Off-stoichiometry in Co2FeSi thin films sputtered from stoichiometric targets revealed by nuclear magnetic resonance
Co2FeSi is predicted to be a half-metallic ferromagnet with an extraordinary high magnetic moment and Curie temperature. However, a low tunnel magneto-resistance ratio, a lower spin polarization and a lower magnetic moment were experimentally observed in thin film samples. Consequently, thin Co2FeSi films of different groups were studied using spin-echo nuclear magnetic resonance (NMR). NMR probes the local hyperfine fields of the active atoms, which strongly depend on the local environment. NMR is thus able to reveal the next neighbouring shells of the Co-59 nuclei in the Co2FeSi thin films. As expected, our NMR study shows the main resonance line corresponding to Co-59 nuclei in the L2(1)…
Seebeck coefficients of half-metallic ferromagnets
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.
Phase-separation-induced changes in the magnetic and transport properties of the quaternary Heusler alloyCo2Mn1−xTixSn
The quaternary Heusler compound ${\text{Co}}_{2}{\text{Mn}}_{1\ensuremath{-}x}{\text{Ti}}_{x}\text{Sn}$ with $x=0$, 0.2, 0.4, 0.5, 0.6, 0.8, and 1 shows a phase separation into the two Heusler compounds, ${\text{Co}}_{2}\text{MnSn}$ and ${\text{Co}}_{2}\text{TiSn}$. Only at the edges of the composition range a slight admixture of Mn and Ti to the respective other phase is observed. This phase separation leads to a distinct microstructure which can be altered by the composition of the material. Pronounced changes in the magnetic and electronic properties take place with varying composition. Two magnetic transitions occur which indicate different Curie temperatures for both phases. The reduct…