DC and AC tunneling magnetoelectric responses of cobalt lateral nanogranular films

Abstract

We demonstrate a new structural optimization of cobalt–(barium fluoride) lateral nanogranular films, achieving independently variable direct current (DC) and alternating current (AC) tunneling effects, in the film plane and out of the plane, respectively. Lateral nanogranular films were successfully fabricated via programmable tandem sputtering. Flat-shaped magnetic Co nanogranules were periodically inserted between dielectric barium fluoride layers of different thicknesses. All the lateral nanogranular films were insulating, with electrical resistivities ρ exceeding 1013 μΩ·cm, even with a Co content as high as 30 at.%. A lateral tunneling magnetoresistance (TMR) effect and vertical tunneling magnetodielectric (TMD) effect were found in the same lateral nanogranular film with 30 at.% Co. For a nanogranular film with lateral Co nanoparticles, the sensitivity of both the TMR and TMD ratio were improved at small magnetic fields compared with conventional films with spherical Co nanoparticles, reflecting its small saturation magnetic field. This layer-ordered metal–insulator nanogranular structure has potential applications in AC/DC hybrid elements as a high-sensitivity magnetic sensor.