Nanomechanical Detection Of Electron Spin Flip PDF Download

Abstract: The focus of this thesis is the detection of mechanical torque generated by electron spin flip in a ferromagnetic-nonmagnetic nanowire attached to an integrated nanoscale torsion resonator. We report direct measurement of this mechanical torque with a sensitivity of 0.1 pN-nm/[Special characters omitted.] . The level of torque sensitivity of our device is an order of magnitude better than typical results in literature. Our approach competes favorably with optical-tweezer detection methods and may enable ultrasensitive measurements of untwisting of DNA and other torque generating molecules, as well as nanomechanical tests of spintronics effects. This novel technique allows us to measure directly the itinerant electron spin polarization independently of the spin diffusion length. The method to detect and control electronic spin is vital to the development of spin-based electronics or spintronics, and spin-based quantum computing. The resonator is a hybrid nano-electro-mechanical device. The central torsional element of the device contains a ferromagnetic-nonmagnetic interface which generates the localized spin-torque. The mechanical torsion of the central element is coupled to an outer mechanical element, capable of transducing the torsional motion into a voltage signal. We derive the fundamental equations describing the spin-torque created by spin currents. Expressions for the expected measured voltage signal and its dependence on the magnetic field, current, and sample orientation are derived from the complete analytical model of the device. We also study the effects of thermal fluctuations and amplifier noise, which limit the measurement sensitivity of our integrated nanomechanical spin-torsion balance. Other relevant physical mechanisms such as the Wiedemann effect, are discussed. Resonators from silicon have been fabricated and their response are measured magneto-motively at temperatures down to 100 millikelvin. We have detected spin-transfer torque generated by polarized spins flipping in a paramagnetic structure. The data sets agree very well with the expected dependence of the torque on current, magnetic field, and its orientation. We have performed control measurements using identical devices without a ferromagnetic-nonmagnetic interface for proper calibration. Additional studies of vibrational energy dissipation and frequency shift in mega hertz range doubly-clamped nanobeams are described. The measurements are performed at millikelvin temperatures, which show reproducible features, similar to those observed in sound attenuation experiments in disordered glasses, consistent with measurements in larger micromechanical oscillators fabricated from single-crystal silicon.