Haiming Yu

Evidence for Thermal Spin-Transfer Torque

Large heat currents are obtained in Co/Cu/Co spin valves positioned at the middle of Cu nanowires. The second harmonic voltage response to an applied current is used to investigate the effect of the heat current on the switching of the spin valves. Both the switching field and the magnitude of the voltage response are found to be dependent on the heat current. These effects are evidence for a thermal spin-transfer torque acting on the magnetization and are accounted for by a thermodynamic model in which heat, charge and spin currents are linked by Onsager reciprocity relations.

High propagating velocity of spin waves and temperature dependent damping in a CoFeB thin film

Spin wave propagation in a magnetron-sputtered CoFeB thin film is investigated. We apply both in-plane and out-of-plane magnetic fields. At room temperature, we find velocities of up to 25 and 3.5u2009km/s, respectively. These values are much larger compared to a thin permalloy film. Analyzing the resonance linewidth, we obtain an intrinsic Gilbert damping parameter of about 0.007 at room temperature. It increases to 0.023 at 5u2009K. CoFeB is a promising material for magnonic devices supporting fast propagating spin waves.

Reciprocal Damon-Eshbach-type spin wave excitation in a magnonic crystal due to tunable magnetic symmetry

We report spin-wave (SW) propagation in a one-dimensional magnonic crystal (MC) explored by all electrical spectroscopy. The MC consists of a periodic array of 255u2009nm wide permalloy nanowires with a small edge-to-edge separation of 45u2009nm. Provoking antiparallel alignment of the magnetization of neighboring nanowires, we unexpectedly find reciprocal excitation of Damon-Eshbach type SWs. The characteristics are in contrast to ferromagnetic thin films and controlled via, both, the external magnetic field and magnetic states. The observed reciprocal excitation is a metamaterial property for SWs and attributed to the peculiar magnetic symmetry of the artificially tailored magnetic material. The findings offer great perspectives for nanoscale SW interference devices.

Current susceptibility of magnetization in spin valves

We observed the second harmonic voltage response of pseudo-spin valves subjected to currents oscillating at frequencies in the sub-kilohertz range. Peaks appear in its magnetic field dependence, with a signal-to-noise ratio equal to or greater than the magnetoresistance response of the same samples. This signal is interpreted as arising from the response of the magnetization to the spin torque induced by current when the magnetic layers are in non-collinear orientations. Thus, the method probes the current susceptibility of the magnetization which is shown to be sensitive to non-collinear states undetectable in the magnetoresistance.