FORC signatures and switching-field distributions of dipolar coupled nanowire-based hysterons

Abstract

Analysis of first-order reversal curves (FORCs) is a powerful tool to probe irreversible switching events in nanomagnet assemblies. As in essence switching events are related to the intrinsic properties of the constituents and their interactions, resulting FORC diagrams contain much information that can be crosslinked and complex to deconvoluate. In order to quantify the relevant parameters that drive the FORC diagrams of arrays of perpendicularly magnetized nanomagnets, we present step-by-step simulations of assemblies of hysterons to determine the specific signatures related to different known inputs. While we explored the consequences of dipolar interactions using either mean field or magnetostatic approaches, we completed by taking the hysteron switching-field distribution (SFD) as either normal or log-normal. We demonstrated that the transition between FORC diagrams composed of an isolated interaction field distribution (IFD) and a wishbone shape operates via the SFD deviation, 𝜎 𝐻 𝑠𝑤 , in the presence of a weakly dispersed interaction field. In the presence of a magnetostatic interaction field, the IFD profile is peaked and a coercive field distribution (CFD) sums to the IFD as 𝜎 𝐻 𝑠𝑤 increases. A transition between IFD+CFD and wishbone shapes is clearly demonstrated as a function of the interaction field deviation 𝜎 𝐻 𝑖𝑛𝑡 . In addition, we demonstrate that whatever the considered cases, 𝜎 𝐻 𝑠𝑤 can be quantitatively extracted from the FORC diagrams within an error inferior to 10%. These findings are of interest for dipolar coupled perpendicularly magnetized nanomagnets, as in assemblies of magnetic nanowires and nanopillars, as well as bit patterned media.

Realizing the Principles for Remote and Selective Detection of Cancer Cells Using Magnetic Nanowires

“…As mentioned above, the ISF signature is also a function of the interaction fields between the MNWs. The interaction field effect on ISF signatures is a broadening (increasing full width at half-maximum, FWHM) and a shift of the ISF peak field depending on the relative strength of the coercivity and interaction fields. − Here, the interaction fields were engineered by the MNW composition (determining the saturation magnetization) and the MNW diameter-to-interwire-distance ratio, which is the interpore distance of the biopolymers. For simplicity, we kept the interpore distances constant, 540 nm, for all biopolymers.…”

Unlocking the decoding of unknown magnetic nanobarcode signatures

“…Moreover, we can improve the decoding rate further in at least two ways. First, we can design and synthesize multi-segmented or multi-component MNWs to engineer the magnetic anisotropy for minimal overlap in nanobarcode signatures [45][46][47][48]. Second, more advanced decoding algorithms based on machine learning can be implemented.…”

Single Diameter Modulation Effects on Ni Nanowire Array Magnetization Reversal

“…In the case of arrays of interacting single domain magnetic nanowires, it is due to the multiplicity of their magnetization reversal occurrences. Resulting typical examples are the extreme cases of the wishbone shape and the distribution extension along the H c axis, arising from a nanowire coercivity distribution respectively with a uniform [31,36] and non-uniform [37] interaction field, as well as the intermediate cases depending on these distribution relative intensity, width, and shape [48]. The second consequence is the possible presence of negative distribution values (ignoring those induced by experimental noise in the FORCs).…”

“…This common feature arises when both the individual switching field and the felted demagnetizing interacting field differ among the magnetic entities. Physically, several causes can produce an analogous feature, such as the lower mean interaction field intensity at the array lateral border [37] or a predominant local magnetostatic interaction field [48]. Here, we may also consider the radial stray field as a source of interaction field non-uniformity.…”