Geometrically enhanced magnetoresistance in ferromagnet–insulator–ferromagnet tunnel junctions (abstract)

Abstract

Ferromagnetic–insulator–ferromagnetic trilayer tunnel junctions show mangetoresistance (JMR) effects of about 16% or greater at room temperature.1 Much larger values of the JMR (100% or more) are observed in low-resistance junctions when the actual tunneling resistance (RT) is comparable to electrode film resistance (RL) over the junction area in our cross-geometry junction measurements.2 For the fixed junction area of 6×10−4 cm2, the measured junction resistance RJ was changed from less than an ohm to several kilohms, by controlling the duration of glow discharge in partial pressure of N2 or O2 to create AlN or Al2O3 tunnel barriers. The ferromagnetic films were CoFe base layer and Co or Ni0.8Fe0.2 top layer. These trilayer junctions show nonvolatile memory effects, are stable and reproducible. The geometrically enhanced large JMR can be qualitatively explained by the nonuniform current flow over the junction area when RT is comparable to RL, in the crossed geometry junction structure. These junctions can be effectively used as magnetic sensors and memory elements.