Janghae Ku

Effective spin injection in Au film from Permalloy

The electrical injection of spin current in the lateral Permalloy/Au/Permalloy spin valve devices was investigated. Clear spin valve effects were found in nonlocal spin valve measurements. The spin diffusion length of Au was evaluated to be 168nm. High spin injection polarization of 26% at 15K was achieved from our samples with low interface resistance. The observed spin injection reveals the highest polarization among the reported values. This work demonstrates the high spin injection polarization through clean interface with low interface resistance.

Electrical spin injection and accumulation in ferromagnetic/Au/ferromagnetic lateral spin valves

Spin injection and accumulation have been investigated for Ni81Fe19∕Au∕Ni81Fe19 lateral spin valves with various separations between spin injector and detector. The spin valve has been studied by using two distinct measurement configurations: the local and nonlocal measurement configurations. For both configurations, a spin valve signal has been found in the wide temperature range from 15to300K, and the magnitude of the spin valve signal decreases as the temperature increases. Based on the nonlocal spin valve signals, we estimate that the spin-diffusion length of a Au film is 85nm and that the spin-injection efficiency is 73% at T=15K.

Spin Valve Effect in Lateral Py/Au/Py Devices

Spin dependent transport was investigated in lateral Py(Ni 81 Fe 19 )/Au/Py spin valve devices. Clear spin valve effect was observed in conventional four-terminal measurement geometry. Higher resistance was found in antiparallel magnetization field of two Py electrodes which is determined by anisotropy magnetoresistance (AMR) measurements. The rectangular shape of spin signal together with good agreement of switching field convinces observed spin valve signal is resulted from effective spin injection and detection. The magnetoresistance ratio decays exponentially with channel length by which spin diffusion length of Au channel was estimated to be 76 ㎚.

Effect of intervening ferromagnet on spin accumulation in Py/Au/Py spin valve device

Nonlocal spin signal is largely dependent on the resistivity of nonmagnetic channel in spin valve devices. Since the resistivity of channel is subjected to change from sample to sample, it is necessary to keep the resistivity as constant as possible. Multiferromagnetic electrodes on single channel are favorable in order to minimize the variation of the resistivity. There is controversial that intervening ferromagnetic electrode may affect spin signal in such a structure. In this experiment, we fabricated Py/Au/Py spin valve devices with multi Py electrodes and measured series of nonlocal signal in various distances of Pys with or without intervening Py electrode aiming at clarifying the controversy.

Inhomogeneous spin injection and detection in the lateral FM/Au/FM spin valve device

Effective spin injection to nonmagnetic material gives rise to spin accumulation at anti-parallel magnetic configuration of two FM electrodes. We performed nonlocal measurement with different voltage and current probe configurations on the lateral Py/Au/Py spin valve devices in order to address the cause of non zero base resistance as well as a large difference of non local signal depending on the location of injecting or detecting probes. 60 nm thick Au film was pattered to define Au channel by electron beam lithography followed by lift off process on an oxidized Si substrate. 80 nm thick Py (Ni81Fe19) electrodes with a different aspect ratio (FM1 : 3um X 0.5um, FM2 : 0.2um X Hum) being separated by a distance of 120 ~ 400 nm are fabricated on a pre-patterned Au channel. The nonlocal measurements were carried out at different voltage probe configurations by the standard ac lock-in techniques at 15 K with an excitation current value of 1 mA.