Spin-transport across semi-crystalline polyvinylidene fluoride thin films in Ta/Co/PVDF/NiFe pseudo spin-valve devices

Abstract

Room temperature magnetoresistance (MR) across semi-crystalline polyvinylidene fluoride (PVDF) thin films in Ta(2 nm)/Co(15 nm)/PVDF/NiFe(28 nm) pseudo-spin-valve devices (PSVs) are systematically investigated by varying PVDF thicknesses from 80 − 230 nm and applied bias voltages up to 100 mV. NiFe, Ta/Co magnetic bottom and top electrodes, and PVDF thin films are deposited by DC magnetron sputtering and spin-coating methods. The structural, microstructural, and magnetic natures have been evaluated using grazing incidence X-ray diffraction, atomic force microscopy, and magneto optic kerr effect systems. Electrical characteristics reveal a maximum MR of ∼0.25 % at 60 mV bias voltage across PVDF-80 nm and ∼0.08 % across PVDF-230 nm & PVDF- 120 nm devices. A constant MR is found across all the devices up to 100 mV applied bias voltages. In addition to the electrical spin injection evaluation, coplanar waveguide ferromagnetic resonance measurements are utilized to validate the spin injection into PVDF layers by estimating the Gilbert damping parameters of NiFe and PVDF/NiFe bilayers. Furthermore, low MR in PSVs is discussed with the parallel spin-dependent conducting channels corresponding to PVDF’s amorphous, alpha, and beta crystalline phases.