Magnetoresistance effect in rubrene-based spin valves at room temperature.

We fabricate spin-valve devices with an Fe3O4/AlO/rubrene/Co stacking structure. Their magnetoresistance (MR) effects at room temperature and low temperatures are systemically investigated based on the measurement of MR curves, current-voltage response, etc. A large MR ratio of approximately 6% is achieved at room temperature, which is one of the highest MR ratios reported to date in organic spin valves. With decreasing measurement temperatures, we observe that the MR ratios increase because of decrease in spin scattering, and the width of the MR curves becomes larger owing to increase in the coercivity of the electrodes at low temperature. A nonlinear current-voltage dependence is clearly observed in these organic spin valves. From the measurement of MR curve for the spin valves with different rubrene layer thickness, we observe that the MR ratios monotonously decrease with increasing rubrene-layer thickness. We discuss the spin-dependent transport mechanisms in these devices based on our experimental results and the present theoretical analysis. Moreover, we note that the devices exhibit smaller MR ratios after annealing compared to their counterparts without annealing. On the basis of atomic force microscopy analysis of the organic films and device resistances, we deduce that the increase of interface spin scattering induced by large surface roughness after annealing most probably leads to reduction in the MR ratios.

Engineered Heusler Ferrimagnets with a Large Perpendicular Magnetic Anisotropy.

Synthetic perpendicular magnetic anisotropy (PMA) ferrimagnets consisting of 30-nm-thick D022-MnGa and Co2MnSi (CMS) cubic Heusler alloys with different thicknesses of 1, 3, 5, 10 and 20 nm, buffered and capped with a Cr film, are successfully grown epitaxially on MgO substrate. Two series samples with and without post annealing at 400 °C are fabricated. The (002) peak of the cubic L21 structure of CMS films on the MnGa layer is observed, even for the 3-nm-thick CMS film for both un-annealed and annealed samples. The smaller remnant magnetization and larger switching field values of CMS (1-20 nm)/MnGa (30 nm) bilayers compared with 30-nm-thick MnGa indicates antiferromagnetic (AFM) interfacial exchange coupling (Jex) between MnGa and CMS films for both un-annealed and annealed samples. The critical thickness of the CMS film for observing PMA with AFM coupling in the CMS/MnGa bilayer is less than 10 nm, which is relatively large compared to previous studies.

Observation of a large spin-dependent transport length in organic spin valves at room temperature.

The integration of organic semiconductors and magnetism has been a fascinating topic for fundamental scientific research and future applications in electronics, because organic semiconductors are expected to possess a large spin-dependent transport length based on weak spin-orbit coupling and weak hyperfine interaction. However, to date, this length has typically been limited to several nanometres at room temperature, and a large length has only been observed at low temperatures. Here we report on a novel organic spin valve device using C(60) as the spacer layer. A magnetoresistance ratio of over 5% was observed at room temperature, which is one of the highest magnetoresistance ratios ever reported. Most importantly, a large spin-dependent transport length of approximately 110 nm was experimentally observed for the C(60) layer at room temperature. These results provide insights for further understanding spin transport in organic semiconductors and may strongly advance the development of spin-based organic devices.