Re-entrant magnetic behaviour in core–shell nanotubes: a Monte Carlo study

This study investigates the re-entrant magnetic behaviour in a core–shell nanotube structure using Monte Carlo simulations within the framework of the Metropolis algorithm. The system comprises mixed spins, modelled with Blume-Capel interactions under different physical conditions. The temperature dependence of magnetisation and susceptibility is systematically explored by varying the crystal field parameter, exchange couplings and external magnetic field. The results reveal a complex phenomenon of re-entrant magnetisation, where the total magnetisation reverses its sign with temperature changes. For specific values of crystal field and interlayer exchange coupling, the system exhibits multiple sign changes in the sublattice magnetisations and a noticeable compensation point. In addition, the application of a strong external magnetic field suppresses the re-entrant effect due to spin alignment stabilisation. These results highlight the tunability of magnetic properties in core–shell nanostructures, offering potential applications in magnetic storage, spintronics and nanoscale sensors.