Sensing anisotropic stresses with ferromagnetic nanowires

Abstract

We have measured the temperature variation of the magnetic anisotropy of Ni nanowires (Ni NW) embedded in freestanding porous anodized aluminum oxide membranes, using DC magnetometry and ferromagnetic resonance. Both techniques show a significant reduction of the uniaxial anisotropy with decreasing temperature. This decrease can be explained by magnetoelastic effects, as Ni NW are subjected to stress due to the difference in thermal expansion coefficients between the nanocomposite materials.Matching our experimental findings with previously measured thermal strains along the Ni NW axis led us to estimate the perpendicular stress. Thus, we postulate the Ni NW as nanometric differential stress sensors.

Effective anisotropy in Fe-Ni nanowire arrays with strong dipolar interaction

“…As mentioned above, previous experiments [30,31] performed to compare FMR and M(H) results show a much closer match between the effective fields resulting from these two measuring conditions. In these experiments, NWs with smaller radii (typically 35 nm or below) are measured, in which more uniform magnetization modes are likely to take place and dipolar interactions are relatively low.…”

“…In these experiments, NWs with smaller radii (typically 35 nm or below) are measured, in which more uniform magnetization modes are likely to take place and dipolar interactions are relatively low. These factors, a more uniform magnetic structure and weak dipolar interactions, are likely to be responsible for the similar anisotropy values reported for FMR and M(H) techniques [30,31], in contrast with our present results. The relevance of the NW diameter in soft arrays is also evidenced by micromagnetic calculations related to the magnetization process in Ni NWs [39], which predict a transition in the predominant reversal mechanism at diameters of about D = 42 nm, with the system changing from a simple domain wall that nucleates and propagates along the wire axis to a reversal mechanism for thicker wires via a localized curling mode.…”

“…The porosity P of our samples is also larger than that reported in [30,31], leading to stronger dipolar interactions between the wires in the array. However, it is remarkable that no negative values for the effective anisotropy field are obtained in our work, even when the traditional expression for magnetostatic interactions in porous systems [18] yields negative effective anisotropy values for porosities above 33% (see Figure 7).…”

“…( 1) a crystalline anisotropy contribution is not considered because of the intrinsic low values observed in these alloys and the fact that the crystallites in the NWs are randomly oriented (as shown by XRD). Magnetoelastic energy terms are also disregarded since the samples were grown near room temperature, so strains related to differential expansion between AAO, and the NW are expected to be negligible [30].…”

Electrodeposition and magnetic properties of Co x Dy1−x nanotube arrays

“…ne-dimensional magnetic nanomaterials, such as the magnetic nanotube, nanowire and arrays of nanotubes or nanowires, have attracted much more attention recently due to their distinctive properties and tremendous application potential [1][2][3][4][5] in a high-density perpendicular magnetic memory device, [6][7][8] magnetic sensor, 9,10) electroacoustic device, 11) damping device 12) and spintronic devices. 13,14) Owing to its unique wire-like shape, one-dimensional nanostructures of transition metals and alloys exhibit higher saturation magnetization and coercivity than their bulk counterpart.…”