Spin Mechanics
Spin is an intrinsically quantum property, characterizing angular momentum. A change in the electron spin state is equivalent to a change in the angular momentum or mechanical torque. Could this torque be measured by nanomechanical torsion resonator? Could an external torque applied to an electron system separate spin polarized states to create a spin battery?
Spin is an intrinsically quantum property, characterizing angular momentum. A change in the electron spin state is equivalent to a change in the angular momentum or mechanical torque. This spin-induced torque has been invoked as the intrinsic mechanism in experiments ranging from the first measurement of angular momentum of photons and g-factor of metals to the magnetization reversal in magnetic multilayers in spintronic devices. A spin-polarized current introduced into a nonmagnetic nanowire produces a torque associated with electron spin flip within the nonmagnetic material.
We have a comprehensive program to explore fundamental spin dynamics in normal and hybrid structures using nanomechanics as a novel tool. Underlying the necessity of studying spin dynamics using nanomechanical measurements is the realization that the spin transport and spin transfer effects invariably involve mechanical torque. Measurements of this torque and associated mechanical parameters enable a novel approach to the study of spin dynamics, complementary to the conventional studies using electronic transport or spectroscopic studies. In particular, we discuss measurement of quantized spin transport, and spin density waves and spin-transfer torques in magnetic multilayers, heterojunctions and antiferromagnetic structures.
Recently, we have performed a direct measurement of this mechanical torque with a sensitivity of 1.0e-22 N-m/rtHz in a ferromagnetic-nonmagnetic nanowire grown on top of an integrated nanoscale torsion oscillator. The unprecedented torque sensitivity of our approach may now enable alternative nanomagnetic devices for spintronics, new approaches to precision measurements of CP-violating forces, and ultrasensitive measurements of untwisting of DNA and other torque generating molecules.