The processional magnetization induced spin current at the interface between CoFeB and Ta has been studied experimentally using spin pumping and inverse spin Hall effect for different thicknesses of CoFeB film down to 1.6 nm. It is found that upon decreasing the thickness of the CoFeB, the frequency of the peak position of the spin pumping signal reduces and dispersion relation of the ferromagnetic resonance changes from a quadratic to a linear behavior indicating the presence of an interfacial perpendicular anisotropy. Furthermore, a nonreciprocal behavior between the spin pumping signal amplitude at positive and negative fields is observed which could be as large as 100%. Our experimental results suggest reduction of the effective demagnetization field and possibly the spin waves nonreciprocal behavior mediated by the Dzyaloshinskii-Moriya interaction at the Ta/CoFeB interface are responsible for the large nonreciprocity of the spin pumping signal.
Bibliographical noteFunding Information:
This work was partially supported by the National Science Foundation Nanoelectronics Beyond 2020 (Grant No. NSF NEB 1124831), NSF MRSEC Program at University of Minnesota (Grant No. DMR-0819885), and by the C-SPIN center, one of six STARnet program research centers. A portion of this work was carried out in the Minnesota Nano Center.
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