Perpendicularly magnetized epitaxial Co/Ni multilayers grown on Ru (0001) layers by alternate monoatomic layer deposition

The hcp stacked B-h-ordered CoNi film was a candidate material to simultaneously have large uniaxial magnetic anisotropy energy (K-u) and a low Gilbert damping constant, which were previously predicted by a first-principles calculation. In this paper, we investigated the film growth condition to form the hcp stacked CoNi layers. [Co(1 ML)/Ni(1 ML)](N) multilayers were epitaxially grown on Al2O3(11-20)/Ru(0001) underlayers by molecular beam epitaxy using an alternate monoatomic layer deposition technique with changing growth temperature (T-s) and repetition number (N). As the results of structural characterizations by x-ray diffraction measurements, it was found that the fcc- and hcp-CoNi phases were mixed in the samples, and the volume fraction of the fcc phase was larger than that of the hcp phase. However, the formation of the hcp-CoNi phase was promoted near the interface with the Ru layer having the hcp structure. The low growth temperature and the small N increased the volume fraction of the hcp phase. The K-u value of 5.1 Merg/cm(3) was achieved for the [Co(1 ML)/Ni(1 ML)](20) multilayer grown at room temperature. In addition, a perpendicularly magnetized film was realized even for the thin sample with N = 5 (2 nm). This means that the Co/Ni multilayers are a thin ferromagnetic material suitable for application to spintronic devices.

Automated summary

This paper investigates the growth conditions of hcp stacked CoNi films with large magnetic anisotropy and low damping constant. The results show that the formation of hcp-CoNi is promoted near the Ru layer with hcp structure, and low growth temperature and small repetition number increase the volume fraction of hcp phase. The multilayers grown at room temperature exhibit high magnetic anisotropy energy and perpendicular magnetization.