Search

First-order reversal curve diagrams, or FORC diagrams, have been studied to determine if the widths of their distributions along the interaction and coercivity axes can be related to the mean-field magnetization dependent interaction field (MDIF). Arrays of nanowires with diameters ranging from 18 up to 100 nm and packing fractions varying from 0.4 to 12% have been analyzed. The mean-field MDIF has been measured using the remanence curves and used as a measuring scale on the FORC diagrams. Based on these measurements, the full width of the interaction field distribution and the full width at half maximum (FWHM) of the FORC distribution profile along the interaction field direction are shown to be proportional to the MDIF, and the relation between them is found. Moreover, by interpreting the full width of the coercive field distribution in terms of the dipolar induced shearing, a simple relation is found between the width of this distribution and the MDIF. Furthermore, we show that the width of the FORC distribution along the coercive field axis is equal to the width of the switching field distribution obtained by the derivation of the DC remanence curve. This was further verified with the switching field distribution determined using in-field magnetic force microscopy (MFM) for very low density nanowires. The results are further supported by the good agreement found between the experiments and the values calculated using the mean-field model, which provides analytical expressions for both FORC distributions.

The fundamental properties of 2D arrays of magnetic nanowires and nanotubes (NWs and NTs) have been well described theoretically, but real systems are subject to certain flaws and imperfections which strongly affect the mechanism and dynamics of magnetization reversal. Therefore, before exploiting the vast potential of magnetic NWs and NTs, there is a need to investigate the materials parameters as well as the field dependent magnetic properties in real systems. Amongst the various issues at stake for a comprehensive understanding of these arrays is the influence of long-range dipolar interactions because these interactions strongly influence the magnetization reversal and thus the switching field distributions (SFD) which plays a significant role for information storage. Particularly, the width of the SFD is important since smaller values of this parameter leads to less recording errors and it is also a measure of the quality of the recording media. Consequently, the understanding and evaluation of the distinct parameters influencing the interactions and the intrinsic SFD in the magnetization reversal process of such arrays is critical for the development of magnetic recording media. It is shown that the intrinsic SFD mostly originates from nonuniformities of the geometrical parameters such as the aspect ratio and the shape of the magnetic nanostructures. This chapter provides an overview of the MFMcharacterization studies undertaken to understand the reversal behavior of 2D arrays of magnetic NWs and NTs at the nanoscale and the motivations to investigate isolated single domain NWs and NTs.

The progress of magnetization reversal of weakly packed ferromagnetic Ni80Fe20 nanowire arrays of different diameters (40, 50, 70 and 100 nm) electrodeposited in polycarbonate membranes was studied by magnetic force microscopy (MFM). For such a low packing density of nanomagnets, the dipolar interactions between neighbouring wires can be neglected. The intrinsic switching field distribution has been extracted from in situ MFM images and its width was found to be considerably smaller than for densely packed nanowire arrays., 4 pages, 5 figures. To appear in Journal of Superconductivity and Novel Magnetism

In the present work, we report on the in situ magnetic force microscopy (MFM) study of the magnetization reversal in two-dimensional arrays of ferromagnetic Ni80Fe20 and Co55Fe45 nanowires(NW) with different diameters (40, 50, 70 and 100 nm) deposited inside low porosity (P, 6 pages, 4 figures, To appear in Journal of Applied Physics

The magnetic properties of arrays of nanowires (NWs) and nanotubes (NTs), 150 nm in diameter, electrodeposited inside nanoporous polycarbonate membranes are investigated. The comparison of the nanoscopic magnetic force microscopy (MFM) imaging and the macroscopic behavior as measured by alternating gradient force magnetometry (AGFM) is made. It is shown that MFM is a complementary technique that provides an understanding of the magnetization reversal characteristics at the microscopic scale of individual nanostructures. The local hysteresis loops have been extracted by MFM measurements. The influence of the shape of such elongated nanostructures on the dipolar coupling and consequently on the squareness of the hysteresis curves is demonstrated. It is shown that the nanowires exhibit stronger magnetic interactions than nanotubes. The non-uniformity of the magnetization states is also revealed by combining the MFM and AGFM measurements., Comment: 7 pages, 5 figures