Structural, Magnetic, and Electric Properties of Pt/Co/Au/Cr₂O₃/Pt Thin Film with Cr₂O₃ Layer below 25 nm

抄録

  Perpendicular exchange bias using magnetoelectric Cr₂O₃ has an electric-field triggered switching ability, and the thickness limit of the Cr₂O₃ layer for inducing this bias is a topic of research. In this paper, we investigated the structural, magnetic, and electric properties of Pt/Co/Au/Cr₂O₃/Pt thin films with a Cr₂O₃ layer in the thickness range of 5.7 to 25 nm. By using a magnetron sputtering method, a well-crystallized Cr₂O₃(0001) layer was formed in 5.7-nm-thick Cr₂O₃. All studied films showed perpendicular magnetic anisotropy. The uniaxial magnetic anisotropy energy density increased as the Cr₂O₃ thickness decreased, and 810±90 kJ/m³ was obtained for the film with 5.7-nm-thick Cr₂O₃. Perpendicular exchange bias was evaluated above 80 K, and an exchange anisotropy energy density of 0.30 mJ/m² was observed for the film with a 25-nm-thick Cr₂O₃ at 80 K. The exchange bias could not be observed below 18 nm. Instead, coercivity enhancement, which yields the exchange bias by precisely controlling interfacial exchange coupling, was observed. The electric resistivity was about 5 × 10⁵ Ωm for the 5.7-nm-thick Cr₂O₃ layer, which is sufficiently high for magnetoelectric applications.