TUD

Molecular spintronics garners much attention in recent several years. Molecules consist of light elements (carbon and hydrogen), which enables to expect long spin coherent length and time if spins are efficiently injected. However, reproducibility and reliability in most of previous studies were still controversial, which was mainly due to a poor interface formation between molecules and ferromagnets.. In order to bypass or solve the interface problems and provide reliable studies, we have introduced molecule-ferromagnet nano-composites, where Co nano-particles were uniformly embedded into a molecular matrix [1-4]. The MR effect via molecules was observed in a broader temperature range, and the MR ratio was 80-500% and 0.3% at 4 K and 300 K, respectively. The large MR ratio exceeds a conventional theoretical limit, which can be attributed to a higher order single spin co-tunneling effect [5] and enhancement of spin polarization at the interface between molecules and ferromagnets [6]. We also introduced graphene as a channel layer in molecular spin valves [7]. We have observed clear spin injection and precession signals by introducing a non-local technique, and also observed robustness of spin polarization of injected spins up to +2.7 V [8]. Furthermore, we have found good accordance between theory and experiment in molecular spintronics by comparing "local" and "non-local" signal intensities in graphene-based spin valves, which was a missing part for constructing a steadfast basis of molecular spintronics [8].

References:
[1]S. Miwa, M. Shiraishi et al., Jpn. J. Appl. Phys. 45, L717 (2006).
[2] S. Miwa, M. Shiraishi et al., Phys. Rev. B76, 214414 (2007).
[3] S. Tanabe, M. Shiraishi et al., Appl. Phys. Lett. 91, 63123 (2007).
[4] H. Kusai, M. Shiraishi et al., Chem. Phys. Lett. 448, 106 (2007).
[5] M. Shiraishi, D. Hatanaka et al., submitted.
[6] M. Shiraishi et al., Appl. Phys. Lett. 93, 53103 (2008).
[7] M. Ohishi, M. Shiraishi et al., Jpn. J. Appl. Phys. 46, L605 (2007).
[8] M. Shiraishi et al., cond-mat arXiv 0810.4592.