Magnetic Anisotropy of Co/Pt Multilayers Evaporated on NaCl(100) Substrates

Abstract

Following deposition of a platinum buffer layer, Co and Pt layers were alternately deposited on a NaCl(100) substrate. Substrate temperatures during the deposition of a Pt buffer layer and Co/Pt multilayers, T S buf and T S Co/Pt, were varied from 300 to 670 K. Co/Pt multilayers as well as a Pt buffer layer was found to grow epitaxially on a NaCl(100) substrate when T S buf exceeded 470 K irrespective of T S Co/Pt. Perpendicular magnetic anisotropy K⊥ Co was as small as -4×106 J/m3 when T S Co/Pt was 300 K and T S buf was 470 or 570 K. However, K⊥ Co increased with increasing T S Co/Pt, becoming positive and almost constant at +5×105 J/m3 when T S Co/Pt was 670 K regardless of T S buf. In-plane torque curves had fourfold symmetry, giving rise to a positive cubic anisotropy constant K1 Co exceeding 105 J/m3 which seems too large to be explained by cubic magnetocrystalline anisotropy.