Active control of magnetoresistance of organic spin valves using ferroelectricity

Organic spintronic devices have been appealing because of the long spin life time of the charge carriers in the organic materials and their low cost, flexibility and chemical diversity. In previous studies, the control of resistance of organic spin valves is generally achieved by the alignment of the magnetization directions of the two ferromagnetic electrodes, generating magnetoresistance.1 Here we employ a new knob to tune the resistance of organic spin valves by adding a thin ferroelectric interfacial layer between the ferromagnetic electrode and the organic spacer. We show that the resistance can be controlled by not only the spin alignment of the two ferromagnetic electrodes, but also by the electric polarization of the interfacial ferroelectric layer: the MR of the spin valve depends strongly on the history of the bias voltage which is correlated with the polarization of the ferroelectric layer; the MR even changes sign when the electric polarization of the ferroelectric layer is reversed. This new tunability can be understood in terms of the change of relative energy level alignment between ferromagnetic electrode and the organic spacer caused by the electric dipole moment of the ferroelectric layer. These findings enable active control of resistance using both electric and magnetic fields, opening up possibility for multi-state organic spin valves and shed light on the mechanism of the spin transport in organic spin valves.

Bistability of Free Cobalt and Iron Clusters

The cobalt and iron clusters CoN, FeN (20 < N < 150) measured in a cryogenic molecular beam are found to be bistable with magnetic moments per atom both {mu}N/N 2{mu}B in the ground states and {mu}N */N {mu}B in the metastable excited states (for iron clusters, {mu}N ~3N{mu}B and {mu}N* N{mu}B). This energy gap between the two states vanish for large clusters, which explains the rapid convergence of the magnetic moments to the bulk value and suggests that ground state for the bulk involves a superposition of the two, in line with the fluctuating local orders in the bulk itinerant ferromagnetism.