單晶鐵三矽薄膜之自旋極化率量測

Determination of Spin Polarization of Ferromagnetic Fe3Si Thin Film

邱亦欣(Yi-Hsin Chiu)

指導教授 ： 郭瑞年 ； 李尚凡 ； 洪銘輝

國立清華大學/理學院/物理學系/碩士(2006年)

https://doi.org/10.6843/NTHU.2006.00626

摘要

無資料

關鍵字

鐵三矽 ； 自旋極化率 ； 點接觸

並列摘要

Fe3Si is a ferromagnet with a Curie temperature of 840K. The small lattice mismatch and good thermal stability led to a clean interface between Fe3Si and GaAs. Furthermore, the DO3 structure of Fe3Si can be considered as a Heusler alloy, making it a good candidate of half metals for effective spin injection.
To determine the spin polarization of Fe3Si, Point-contact Andreev reflection (PCAR) spectrum was measured at 4.2K by driving a Pb tip in contact with a gold-capped Fe3Si film using a differential screw mechanism. The conductance-voltage characteristics showed a central peak with a height ratio of 1.17, as attributed to the spin polarization of Fe3Si suppressing the Andreev reflection and the interface barrier.
By fitting the depth of the dip in the central peak with the modified Blonder-Tinkham-Klapwijk (MBTK) model, we extracted spin polarization ranging from 38% to 46% under various contact conditions. Notable decrease of polarization value P with the increasing of interface barrier Z was observed, indicating possible spin-dependent scatterings. The intrinsic polarization P is extracted from the extrapolation in the limit of Z=0 by polynomial fits, and yielded a value of 45±5%.
An unexpected broadening, however, was observed at large bias, which could possibly due to scatterings not accounted for properly by the MBTK theory, since the spectra tends to be broader when the contact resistance is decreased.
To simulate the effect of the unexpected scatterings, we set the temperature T as a fitting parameter Teff and obtained a good agreement between the experimental and theoretical curves. The extracted P ranges from 32% to 50 %, and showed similar P-Z dependence. The intrinsic polarization is 49±5% by extrapolation to Z=0. In both data analyses, we found no substantial discrepancy in the extracted value of spin polarization.

並列關鍵字

Fe3Si ； spin polarization ； point contact