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Exceptionally Strong Spin-Transfer in Single Ni Nanoparticles

This letter presents studies of spin-transfer efficiency in electron transport via discrete electron-in- a-box levels in individual nanometer-scale Ni particles at 0.06K temperature. In a strong magnetic field, the spin-transfer rates are estimated by measuring the amplitudes of the Zeeman splitting of the levels. We find that the spin- and the charge-transfer rates are comparable, demonstrating significant enhancement of the spin-transfer efficiency compared to that in larger magnets. In a low magnetic field, we find an additional energy splitting as evidence that the spin-transfer rate is far higher than the charge-transfer rate. The effect is explained in terms of the strong mesoscopic spin- orbit torques, which are exerted on the magnetization in response to sequential electron tunneling.