Magnetic nanotubes

 

The trusty sphere remains the preferred shape for nanoparticles but this geometry leaves only one surface for modification, complicating the generation of multifunctional particles. Thus, a technology that could modify differentially the inner and outer surfaces would be highly desirable. Since the discovery of carbon nanotubes by Iijima in 1991, intense attention has been paid to hollow tubular nanostructures because of their particular significance for prospective applications. In 2002 Mitchell et al. used silica nanotubes offering two easy-to-modify surfaces. More recently, magnetic nanotubes have been grown that 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. Additionally, current models for magnetoviscosity suggest that replacing the spherical nanoparticles of a conventional ferrofluid with magnetic nanotubes would lead to a stronger field-induced viscosity enhancement and a much improved stability against shear thinning – two important parameters for technological exploitation of the magnetoviscous effect. In this way tiny magnetic tubes could provide an unconventional solution to several research problems and a useful vehicle for imaging and drug delivery applications.

 

Although the magnetic behavior of nanowires has been intensely investigated, tubes have received less attention; in spite of the additional degree of freedom they present; not only the length L and radius R can be varied, but also the thickness of the wall, dw. Changes in thickness are expected to strongly affect the mechanism of magnetization reversal, and thereby, the overall magnetic behavior. However, systematic experimental studies on this aspect were lacking for a long time, mostly due to difficulty in preparing ordered nanotube samples of very well-defined and tunable geometric parameters. Up to now a number of methods, including atomic layer deposition, hydrothermal pyrolysis and template-based growth, have been developed for the fabrication of nanotubes. Magnetic materials used for formation of nanotubes include Ni [1,2], Co [2,3], Fe, CoNi, CoFe2O4, FeNi, FeTi, and Fe3O4 [4-6]

 

Together with the experimental progress, theoretical calculations and numerical simulations for nanotubes have been performed extensively, dealing with the stable states [7,8], magnetostatic interactions [9], magnetotransport properties, properties of domain walls [1,2,4-6,10,11], and switching of domain wall chiralities. Besides, Weber et al. investigated the behavior of magnetization states in individual Ni nanotubes by sensitive cantilever magnetometry. It is noteworthy that we have enough experience investigating the magnetic properties of magnetic nanotubes. So far our studies have focused on the mechanisms of the magnetization reversal by analytical calculations and micromagnetic simulations. However, we have recently acquired the first set of atomic layer deposition in Chile (Savannah S100), and the second in Latin America, which places us in a unique position to carry out the synthesis of these nanostructures.

 

[1] J. Escrig, M. Daub, P. Landeros, K. Nielsch, D. Altbir, Angular dependence of coercivity in magnetic nanotubes, Nanotechnology 18, 445706 (2007).

[2] Mariana P. Proenca, Celia T. Sousa, Joao Ventura, Joao P. Araujo, Juan Escrig, Manuel Vázquez, Crossover between magnetic reversal modes in ordered Ni and Co nanotube arrays, SPIN 2, 1250014 (2012).

[3] M. P. Proenca, C. T. Sousa, J. Escrig, J. Ventura, M. Vázquez, J. P. Araujo, Magnetic interactions and reversal mechanisms in Co nanowire and nanotube arrays, Journal of Applied Physics 113, 093907 (2013).

[4] J. Escrig, J. Bachmann, J. Jing, M. Daub, D. Altbir, K. Nielsch, Crossover between two different magnetization reversal modes in arrays of iron oxide nanotubes, Physical Review B 77, 214421 (2008).

[5] Julien Bachmann, Juan Escrig, Kristina Pitzschel, Josep M. Montero Moreno, Jing Jing, Detlef Gorlitz, Dora Altbir, Kornelius Nielsch, Size effects in ordered arrays of magnetic nanotubes: Pick your reversal mode, Journal of Applied Physics 105, 07B521 (2009).

[6] Ole Albrecht, Robert Zierold, Sebastian Allende, Juan Escrig, Christian Patzig, Bernd Rauschenbach, Kornelius Nielsch, Detlef Gorlitz, Experimental evidence for an angular dependent transition of magnetization reversal modes in magnetic nanotubes, Journal of Applied Physics 109, 093910 (2011).

[7] J. Escrig, P. Landeros, D. Altbir, E. E. Vogel, P. Vargas, Phase diagrams of magnetic nanotubes, Journal of Magnetism and Magnetic Materials 308, 233-237 (2007).

[8] J. Escrig, P. Landeros, D. Altbir, E. E. Vogel, Effect of anisotropy in magnetic nanotubes, Journal of Magnetism and Magnetic Materials 310, 2448-2450 (2007).

[9] J. Escrig, S. Allende, D. Altbir, M. Bahiana, Magnetostatic interactions between magnetic nanotubes, Applied Physics Letters 93, 023101 (2008).

[10] P. Landeros, S. Allende, J. Escrig, E. Salcedo, D. Altbir, E. E. Vogel, Reversal modes in magnetic nanotubes, Applied Physics Letters 90, 102501 (2007).

[11] S. Allende, J. Escrig, D. Altbir, E. Salcedo, M. Bahiana, Angular dependence of the transverse and vorte modes in magnetic nanotubes, The European Physical Journal B 66, 37-40 (2008).