Spin-dependent tunneling in discontinuous Co–SiO2 magnetic tunnel junctions

Abstract

Discontinuous magnetic tunnel junctions (DMTJs) are an alternate system to the magnetic tunnel junctions (MTJ) currently being considered for magnetoresistance (MR) sensors. The DMTJs are easier to fabricate and more robust than the MTJs. The nominal film structure is ${\mathrm{SiO}}_{\mathrm{2}}\text{(20\hspace{0.17em}Å)/}\mathrm{Co}{\mathrm{(t}}_{\mathrm{Co}}\mathrm{)/}{\mathrm{SiO}}_{\mathrm{2}}\text{(30\hspace{0.17em}Å)/}\mathrm{Co}{\mathrm{(t}}_{\mathrm{Co}}\mathrm{)/}{\mathrm{SiO}}_{\mathrm{2}}\text{(20\hspace{0.17em}Å),}$ in which the thin Co layers are discontinuous, in the form of nanoparticles. Magneto-transport measurements were made perpendicular to the film plane on macroscopic junctions for in-plane applied magnetic fields. The results, for these films with only two magnetic layers, are similar to those of the discontinuous multilayers previously reported. The MR response is relatively sharp and almost linear at low magnetic fields and is reproducible from one junction to another. This MR (defined as ${\mathrm{\Delta V/V}}_{\max }$ ) is weakly temperature dependent with a maximum between 4 and 300 K. The MR and the magnetization at low temperature suggest ferromagnetically coupled particles, which switch in lower magnetic fields than noninteracting particles.