Introducing artificial length scales to tailor magnetic properties

Abstract

Magnetism is a collective phenomenon. Hence, a local variation on the nanoscale of material properties, which act on the magnetic properties, affects the overall magnetism in an intriguing way. Of particular importance are the length scales on which a material property changes. These might be related to the exchange length, the domain wall width, a typical roughness correlation length, or a length scale introduced by patterning of the material. Here we report on the influence of two artificially created length scales: (i) ion erosion templates that serve as a source of a predefined surface morphology (ripple structure) and hence allow for the investigation of roughness phenomena. It is demonstrated that the ripple wave length can be easily tuned over a wide range (25–175 nm) by varying the primary ion erosion energy. The effect of this ripple morphology on the induced uniaxial magnetic anisotropy in soft magnetic Permalloy films is studied. Only below a ripple wavelength threshold (≈60 nm) is a significant induced magnetic anisotropy found. Above this threshold the corrugated Permalloy film acts as a flat film. This cross-over is discussed in the frame of dipolar interactions giving rise to the induced anisotropies. (ii) Ion implantation through a lithographically defined mask, which is used for a magnetic property patterning on various length scales. The resulting magnetic properties are neither present in non-implanted nor in homogeneously implanted films. Here new insight is gained by the comparison of different stripe patterning widths ranging from 1 to 10 μm. In addition, the appearance of more complicated magnetic domain structures, i.e. spin-flop domain configurations and head-on domain walls, during hard axis magnetization reversal is demonstrated. In both cases the magnetic properties, the magnetization reversal process as well as the magnetic domain configurations depend sensitively on the artificially introduced length scale.