Invited Paper MI-WeA9
Spintronic Effects in Molecular Materials: The Past, Present, and Future

Wednesday, October 20, 2010, 4:40 pm, Room Zuni

In this talk I will introduce the general concepts of spintronics and highlight some of the key experimental results that have catalyzed the emerging research area known as “organic spintronics”. The confluence of spin-electronics, which combines transition metal ferromagnets and inorganic semiconductors, and molecular-electronics, which combines organic semiconductors and non-magnetic metals, has lead to the evolution of organic spintronics. Furthermore, the development of organic light emitting diodes and organic photovoltaic cells has proven that molecular thin films can reliably function as the active layer in commercial products. Consequently it often envisioned that spin dependent conduction in organic-based semiconductors, rather than traditional charge transport, can be manipulated and detected to fabricate low-power, non-volatile, multifunctional devices because electron spin coupling to orbital angular momentum and nuclear spin is weak. Recent experimental evidence is beginning to demonstrate this view is too simplistic and hyperfine coupling is very important in the hopping transport mechanism characteristic of disordered organic semiconductors.

The focus of this talk will be on the phenomena of magnetoresistance; specifically in vertical device structures with conducting electrodes used to separate an organic semiconductor layer(s). In many laboratories around the world such devices are observed to change resistance when placed in an external magnetic field. If both electrodes are magnetic and the change in the resistance corresponds to the coercive fields of the electrodes, then the magnetoresistance can be interpreted as spin-polarized injection, transport, and ejection of carriers from one ferromagnetic layer, through the non-magnetic spacer layer, and into the second ferromagnetic layer, respectively. However, when neither of the electrodes is magnetic the magnetoresistance must arise some other phenomena and there are several competing theories to describe the effects. The bulk of this talk will be devoted to reviewing case studies from the former class of devices, since there are well-accepted criteria to support the interpretation of device magnetoresistance when using magnetic electrodes. In addition I will cite examples where the interfaces of the devices have been examined by surface sensitive spectroscopy/microscopy techniques and correlated to device performance. Finally I will conclude by recommending some new experiments that could reveal more knowledge of the fundamental spintronics effects in molecular materials and suggest some possible applications.