Nonlocal Spin Detection Research Articles

Non-local electrical spin injection and detection in germanium at room temperature

Non-local carrier injection/detection schemes lie at the very foundation of information manipulation in integrated systems. This paradigm consists in controlling with an external signal the channel where charge carriers flow between a “source” and a well separated “drain.” The next generation electronics may operate on the spin of carriers in addition to their charge and germanium appears as the best hosting material to develop such a platform for its compatibility with mainstream silicon technology and the predicted long electron spin lifetime at room temperature. In this letter, we demonstrate injection of pure spin currents (i.e., with no associated transport of electric charges) in germanium, combined with non-local spin detection at 10 K and room temperature. For this purpose, we used a lateral spin valve with epitaxially grown magnetic tunnel junctions as spin injector and spin detector. The non-local magnetoresistance signal is clearly visible and reaches ≈15 mΩ at room temperature. The electron spin lifetime and diffusion length are 500 ps and 1 μm, respectively, the spin injection efficiency being as high as 27%. This result paves the way for the realization of full germanium spintronic devices at room temperature.

Aging effect of spin accumulation in non-local spin valves

A temporal evolution of spin accumulation of Co/MgO/Ag spin valves have been studied by using the nonlocal spin detection technique over almost a 3-month period in the ambient environment after the fabrication of the devices. Three different stages of the spin accumulation are first observed due to aging effect. The aging effect comes from two contributions–the gradual oxidation of the Ag/MgO and MgO/Co interfaces at the junctions’ areas which arises from the annealing process and the oxidation of the side surfaces of the Ag channels. The theories of S. Takahashi and A. Fert are introduced to evaluate the different evolution stages of spin accumulation.

Asymmetric spin absorption across a low-resistance oxide barrier

An unconventional method of nonlocal spin detection is demonstrated in mesoscopic lateral spin valves at room temperature. Clear nonlocal spin signals are detected between the two ends of an extended ferromagnetic spin detector. This is different from the conventional method in which the nonlocal voltage is measured between the spin detector and the nonmagnetic channel. The results can be understood as spatially non-uniform absorption of a pure spin current into the spin detector across a low-resistance oxide interface.

Temperature dependent spin precession measurements in trilayer graphene utilizing co/graphene contacts

The temperature dependence of the spin lifetime and spin diffusion coefficient of exfoliated multilayer graphene is measured using nonlocal spin detection and spin precession measurements. Low impedance cobalt contacts are utilized for spin injection and readout. A decrease in spin lifetime with increasing temperature is observed as well as an increase in the spin diffusion coefficient with increasing temperature. This observation provides some insight into the relevant spin relaxation mechanisms that are occurring in this trilayer graphene sample.

Studies of Al2O3 barriers for use in tunnel junctions for nonlocal spin detection experiments

Aluminum oxide films were grown on Si under ultrahigh vacuum conditions for use as tunnel barriers in spin injection studies. X-ray photoelectron spectroscopy was performed to characterize the film stoichiometry. It was observed that all the aluminum was bonded to the oxygen for the films grown in 1 nm steps. Whereas the 2 nm sample grown in one 2 nm step left a partially unoxidized aluminum film. Current-voltage measurements were performed and fitted to a tunnel model. The resistance area products fall within the range needed for spin injection and nonlocal readout.

Gate control of spin transport in multilayer graphene

We experimentally studied the gate voltage dependence of spin transport in multilayer graphene (MLG) using the nonlocal spin detection technique. We found that the spin signal is a monotonically decreasing linear function of the resistance of MLG, which is characteristic of the intermediate interfacial transparency between the MLG and the ferromagnetic electrodes (Co). The linear relation indicates a large spin relaxation length significantly exceeding 8μm. This shows the superiority of MLG for the utilization of the graphite-based spintronic devices.