Off-stoichiometry in Co2FeSi thin films sputtered from stoichiometric targets revealed by nuclear magnetic resonance

被引:17
作者
Wurmehl, Sabine [1 ]
Kohlhepp, Juergen T. [1 ]
Swagten, Henk J. M. [1 ]
Koopmans, Bert [1 ]
Blum, Christian G. F. [2 ]
Ksenofontov, Vadim [2 ]
Schneider, Horst [3 ]
Jakob, Gerhard [3 ]
Ebke, Daniel [4 ]
Reiss, Guenter [4 ]
机构
[1] Eindhoven Univ Technol, Dept Appl Phys, NL-5600 MB Eindhoven, Netherlands
[2] Johannes Gutenberg Univ Mainz, Inst Anorgan & Analyt Chem, D-55099 Mainz, Germany
[3] Johannes Gutenberg Univ Mainz, Inst Phys, D-55099 Mainz, Germany
[4] Univ Bielefeld, Dept Phys, D-33501 Bielefeld, Germany
关键词
TUNNEL MAGNETORESISTANCE; HEUSLER; ALLOYS; NMR;
D O I
10.1088/0022-3727/42/8/084017
中图分类号
O59 [应用物理学];
学科分类号
摘要
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) environment but also additional resonance lines at the high frequency site of the main line with a spacing between adjacent resonance lines of 32 MHz. The additional resonance lines correspond to Co-59 with more Fe next neighbours than expected for the L2(1) type ordering, which is interpreted as the formation of an off-stoichiometric film yielded by sputtering from a stoichiometric target. The analysis of the NMR data and a comparison with off-stoichiometric bulk samples reveals the composition of the thin films to be about Co2Fe(Si0.92Fe0.08). This off-stoichiometry might explain the observed deviations from the expected behaviour.
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页数:7
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