Change in the magnetic configurations of tubular nanostructures by tuning dipolar interactions

• Published in: arXiv.org 2018-06
• Main Authors: Salinas, H D, Restrepo, J, Iglesias, Òscar
• Format: Article
• Language: English
• Subjects: Aspect ratio; Computer simulation; Cylinders; Ferromagnetism; Lattice vibration; Nanotubes; Order parameters; Phase diagrams; Vorticity
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.1806.01040

We have investigated the equilibrium states of ferromagnetic single wall nanotubes by means of atomistic Monte Carlo simulations of a zig-zag lattice of Heisenberg spins on the surface of a cylinder. The main focus of our study is to determine how the competition between short-range exchange (J) and long-range dipolar (D) interactions influences the low temperature magnetic order of the nanotubes as well as the thermal-driven transitions involved. Apart from the uniform and vortex states occurring for dominant J or D, we find that helical states become stable for a range of intermediate values of g = D=J that depends on the radius and length of the nanotube. Introducing a vorticity order parameter to better characterize helical and vortex states, we find the pseudo-critical temperatures for the transitions between these states and we establish the magnetic phase diagrams of their stability regions as a function of the nanotube aspect ratio. Comparison of the energy of the states obtained by simulation with those of simpler theoretical structures that interpolate continuously between them, reveals a high degree of metastability of the helical structures that might be relevant for their reversal modes.