Theoretical Investigation Of Spin-dependent Transport In Organic Magnetic Devices

Spintronics is a new field of growing interest which mainly investigates spincreation and annihilation，electron spin injection, spin-dependent transport and buildsfunctional devices based on organic polymer. Organic materials have a lot ofadvantages such as its low price，ease of processing in large areas and easily beingtailored by chemical or physical methods compared with inorganic materials. Andorganic materials are so softness that it can easily adjust its configuration to form astable interface with other substance. Organic materials have abundant properties inoptics, electronics and magnetics. Right now Organic Light Emitting Diodes (OLED)and organic display devices have been put into application.Two kinds of devices are mainly investigated now. The first one is ferromagneticmetal/organic/ferromagnetic metal (FM/O/FM) structure, these devices are mainlyused to study the electron spin injection from ferromagnetic metal to organicpolymers, the spin-dependent transport in organic materials and the phenomemon ofmagnetoresistance. The second one is metal/organic ferromagnetic/metal (M/OF/M)structure. These devices are mainly based on the magnetic properties of the organicmagnetic polymer. There are two kinds of organic magnetic materials right now. Thefirst kind is non-pure organic magnetic materials which mainly containsmacromolecule metal complex and charge transfer polymers such as［{Mn (hfac)2}3·R2］and M[ TCNE]x·yS. The second one is pure organic magnetic materialswithout metal element, poly-BIPO，m-PDPC and pyrro-PAN for example.A M/OF/M structure device is investigated in this paper. The organic magneticpolymer poly-BIPO is used as the interlayer of the device. We investigated: effects ofatomic disorder of lattice configuration and the orientation disorder of side radicalspins on the spin polarized transport through a metal/organic-ferromagnet/metal structure; and effect of proportion on rectification in organic co-oligomer spinrectifiers with the method of SSH model coupled with Green’s function,The results show that: 1. The atomic disorder reduces the threshold voltage of thedevice and suppressed the conducting current. The staircase structure of thecurrent-voltage curve for a molecular device is eliminated when the disorder isenhanced. The orientation disorder of side radical spins decreased the spin splitting ofmolecular energy levels, which increases the threshold voltage of the device, andlowed the current and its spin polarization at a low bias. 2. When an electron goes intothe molecule, it forms a quasi-particle similar to polaron in polyacetylene, and twosame quasi-particles are formed when two electrons with same spin go into themolecule. When two electrons with different spins go into the molecule, twoquasi-particles similar to soliton are formed in the molecule..