Magnetostatic interactions between magnetic nanotubes

Abstract

The investigation of interactions between magnetic nanotubes is complex and often involves substantial simplifications. In this letter an analytical expression for the magnetostatic interaction, taking into account the geometry of the tubes, has been obtained. This expression allows for the definition of a critical vertical separation for relative magnetization between nanotubes and can be used for tailoring barcode-type nanostructures with prospective applications such as biological separation and transport.Since the discovery of carbon nanotubes by Iijima in 1991, 1 intense attention has been paid to tubular nanostructures. Because of their geometry, nanotubes offer prospective applications in catalysis, 2,3 sensors, 4 and biological separation and transport.3,5-7 In particular, magnetic nanotubes are the focus of growing interest due to the existence of techniques that lead to the production of highly ordered arrays.8-10 These particles offer an additional degree of freedom as compared to nanowires; not only can the length, L, and external radius, R, be varied, but also the internal radius, a. In this way, nanotubes may be suitable for applications in biotechnology, where magnetic nanostructures with low density, which can float in solutions, become much more useful for in vivo applications.11 These tiny magnetic tubes could provide an unconventional solution for several research problems, and a useful vehicle for imaging and drug delivery applications. 7,12In such systems changes in thickness are expected to strongly affect the mechanism of magnetization reversal 13 and, thereby, the overall magnetic behavior. Also interactions play a fundamental role, modifying the magnetic behavior of the particles. Clearly, for the development of magnetic devices based on those arrays, knowledge of the magnetostatic interaction between the tubes is of fundamental importance. But as usual the effects of interparticle interactions are complicated by the fact that the dipolar field felt by each element depends upon the magnetization state of all the elements in the array. In a previous work by Lee et. al., 14 multisegmented metallic nanotubes with a bimetallic stacking configuration along the nanotube axes were prepared and investigated. These particles exhibit different magnetic behaviors, which encourage a study about the magnetostatic interactions between the stacking. Due to the very narrow hysteresis loops that are obtained, the influence of the interactions is not easily identifiable from magnetization curves, and then a theoretical study can shine light on this problem.The purpose of this letter is to develop an analytical model for the full long-range magnetostatic interaction between two nanotubes exploring the possibility of varying the magnetic coupling as a function of the tubes position. The geometry of the tubes is characterized by their external and internal radii, R and a, respectively, and length L. It is convenient to define the ratio β ≡ a/R, so that β = 0 represents a solid cylinder (wire) and β close t...

Electrochemical syntheses of soft and hard magnetic Fe50Pd50-based nanotubes and their magnetic characterization

“…However, this provides a simplified approach to determining the magnetostatic interaction. Escrig et al [19] calculated the interaction energy between two identical nanotubes, where the interaction energy was found to decrease with an increasing interwire distance and a decreasing tube-wall thickness. Since the magnetocrystalline anisotropy (H ma ) of fcc Fe-Pd is very low, the last term in the equation is negligible, and therefore the effective anisotropy originates from the shape anisotropy, which is reduced by the magnetostatic interactions between the tubes.…”

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“…Because of their inherently small magnetic moment, experimental investigations have often been conducted on large ensembles. The results, however, are difficult to interpret due to stray-field interactions and the distribution in size and orientation of the individual nanotubes [12,[14][15][16][17][18]. In a pioneering work, Wernsdorfer et al [19] investigated the magnetic reversal of an individual Ni nanowire at 4 K using a miniaturized SQUID.…”

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“…We denote by M 1 = M s m 1 and M 2 = M s m 2 the two magnetic moments of the two chains. In the limit of homogeneous chains with the magnetization aligned along the chains axis, Escrig et al 17 In the present work, we consider the general case involving anisotropy and an applied magnetic field with arbitrary orientation. Therefore, the magnetic moments M 1 and M 2 may adopt orientations that are not necessarily collinear with each other and/or with the chains axes.…”