Influence of radial and tangential anisotropy components in single wall magnetic nanotubes. A Monte Carlo approach

• Published in: Physica A Vol. 466; pp. 440 - 449
• Main Authors: Agudelo-Giraldo, J.D., Morales-Rojas, S., Hurtado-Marín, V.A., Restrepo-Parra, E.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15.01.2017
• Subjects: Magnetocrystalline anisotropy; Radial and tangential states; Single wall nanotubes; Transition temperatures; Magnetocrystalline anisotropy; Transition temperatures; Single wall nanotubes; Radial and tangential states
• ISSN: 0378-4371; 1873-2119
• DOI: 10.1016/j.physa.2016.08.030

Magnetic behaviour of nanotubes with square cell has been studied by the Monte Carlo Method, under the Metropolis algorithm and Heisenberg model. The Hamiltonian used includes nearest neighbour exchange interaction and radial and tangential direction for uniaxial anisotropy. Periodic boundary conditions were implemented at the sample’s edges. Simulations were carried out varying the nanotube’s diameter by changing the number of magnetic moments per ring and anisotropy values. Two transition temperatures were identified corresponding to states where moments were aligned as either ferromagnetic type or anisotropy direction. At low temperatures and low anisotropy values, the system exhibited a ferromagnetic alignment; as the anisotropy was increased, and continued in the low temperature range, spins were aligned in the anisotropy (radial or tangential) direction. As the temperature was increased, spins were reoriented in the ferromagnetic direction, generating a radial (tangential) anisotropy to ferromagnetic transition temperature. When the temperature continued increasing, the system transited toward the paramagnetic phase, appearing a ferromagnetic to paramagnetic transition phase temperature. In several cases studied here, between these two transition temperatures (anisotropy to ferromagnetic and ferromagnetic to paramagnetic transition phases), the magnetization of the system exhibited instabilities. These instabilities are caused because of the influence of the anisotropy values and the diameter of the nanotubes on the magnetic domains formation. As a consequence, there exist anisotropy values and diameters where metastable states were formed. •Magnetic behaviour of nanotubes with square cell has been studied by the Monte Carlo Method.•Competition between exchange interaction and radial and tangential anisotropy is analysed.•Ferromagnetic, radial or tangential and paramagnetic phases depend on anisotropy constant and temperatures values.