Anisotropic Magnetoresistance in NiFe-Based Polymer Spin Valves

Precise evaluation of magnetoresistance (MR) with the identified transport mechanism is one of the key points in organic spin-valve (OSV) devices. To investigate the origin of the spin-valve-like signal in polymer spin valve with a vertical structure of NiFe/P3HT/AlO _x/Co, the magnetic response measurements in the rotated magnetization direction were established in different well-designed device configurations. We identified the significant influence of anisotropic MR (AMR) and further induced tunneling AMR in NiFe electrodes contributing to the total MR signal. These findings suggest that the mechanisms responsible for the transport mode in polymer spin-valve devices also strongly depend on the interface between the ferromagnetic electrodes and organic semiconductor layer. Even for the spin-valve-resembled MR response with distinct parallel and antiparallel states, carefully controlled experiments such as temperature-dependent and angle-dependent measurements should always be performed to track down the injected spin-polarized carriers. Our thorough experiments and analyses may shed light on the effective MR signal evaluation in OSVs and spin-related parameters with transport mechanism identification.