Study Of Phase Transition And Magnetization Characteristics On Nanotube

The hollow characteristics of magnetic nanotubes, making their performance haveunique physical properties, such as surface effects, excellent absorption properties, etc.As a result, magnetic nanotubes have a lot of potential applications in chemistry andbiology, like magnetic recording, drug loads, catalytic and targeted therapies. Therefore,study on the microcosmic mechanism of phase transition and magnetic properties have agreat significance. In this paper, we established the microscopic theoretical model of ahexagonal and a square nanotube with both existence of single-ion anisotropies andtransverse fields, and investigated the dependence of phase transition and physicalproperties of magnetic nanotubes on physical parameters of magnetic nanotubes in detail.Magnetization curves of the hexagonal ferrimagnetic nanotube exhibit Q-type,P-type and N-type, which are supposed in Néel theory. There is a new curve types in ourstudy, which has two compensation points in magnetization curve. This phenomenon hasbeen confirmed in the research of the dependence of compensation temperature onvarious parameters. With the variation of single-ion anisotropies, transverse fields andexchange interaction, compensation temperature curves are both appeared the regionwhich contains two compensation points. Especially, the system will have two regionswhich contain two compensation points whenD aJachanges. In addition, the shapesof the compensation temperature curves are versatile, like S or octopus type. Phasetransition temperature increases with the increase of single-ion anisotropies and surfaceexchange interaction, and decreases with the increase of transverse fields and interlayerexchange interaction. WhenD aJaand aJachanges, the phase transitiontemperatures have thresholds. The curve of initial susceptibility and specific heat appearsa typical secondary phase transition characteristics at phase transition point. Internalenergy is rapidly increased as the temperature rises until it reaches a phase transition atthe point of inflection point and increased slowly after the phase transition point.Coercivity decreases with the decrease ofDb JaandJ bJa, and increases with the decrease of aJa. The competition of physical parameters resulting in metastable stateoccurs, hysteresis loops exhibits more than one loop.The shape of total magnetization of the square nanotube system is great influencedby surface sublattice. Within certain parameters, magnetization curve appears two orthree compensation points. Compared with the same structure of nanowires, nanotubeshave smaller absolute values of total magnetization and lower phase transitiontemperature. The variation of initial susceptibility, phase transition temperature, internalenergy and specific heat are similar with the hexagonal nanotube. Hysteresis loops alsoexhibits more than one loop.