Systematic tuning of segmented magnetic nanowires into three-dimensional arrays of ‘bits’

Abstract

A method is presented for the preparation of a three-dimensional magnetic data storage material system. The major ingredients are an inert nanoporous matrix prepared by anodization and galvanic plating of magnetic and non-magnetic metals in wire shape inside the cylindrical pores. The individual nanomagnets consist of a nickel–cobalt alloy, the composition of which is tuned systematically by adjusting the electrolytic bath composition at one optimal applied potential. The lowest magnetocrystalline anisotropy is obtained at the composition Ni₆₀Co₄₀, as quantified by superconducting quantum interference device magnetometry. Wires of this composition experience a pinning-free propagation of magnetic domain walls, as determined by single-wire magneto-optical Kerr effect magnetometry. Adding copper into the electrolyte allows one to generate segments of Ni₆₀Co₄₀ separated by non-magnetic copper. The segment structure is apparent in individual nanowires imaged by scanning electron microscopy, UV-photoelectron emission microscopy, and transmission electron microscopy. The single-domain structure of the wire segments is evidenced by magnetic force microscopy.