Giant spin-polarization and magnetic anisotropy of nanostructures at surfaces

Abstract

We present spin-polarized scanning tunneling microscopy measurements demonstrating spin-polarizations of up to 80 % for Co islands on a Pt(111) surface and a tunnel magneto resistance of 850 % between the islands and an anti-ferromagnetic Cr-coated W-tip. These values are stable up to ±0.7 V bias. We report on the magnetic moments and anisotropy energies of two-dimensional Co islands on Pt(111) comprising only a few atoms. Our results show the correlation between orbital moments and magneto-crystalline anisotropies and reveal that both properties strongly depend on the lateral atomic coordination. The anisotropy of single adatoms is found to be 200 times the Co hep bulk value. We also present well ordered superlattices of Co islands self-assembled on Au(788). The particles have uniaxial out-of-plane magnetization and no dipolar interactions. They present a model system for ultra-high density storage media since they have the most uniform anisotropy energies and the highest density of non-interacting particles so far realized. © 2006 The Surface Science Society of Japan.