Volume 58, Number 4, May 2002
|Page(s)||603 - 609|
|Section||Condensed matter: electronic structure, electrical, magnetic, and optical properties|
|Published online||01 May 2002|
Thermodynamics of two-dimensional magnetic nanoparticles
Departamento de Física, Universidad Técnica
Federico Santa María Valparaíso, Chile
2 Max-Planck Institut für Festkörperphysik - D-70569 Stuttgart, Germany
3 Departamento de Física, Universidad de Santiago de Chile - Av. Ecuador 3493, Santiago, Chile
4 Instituto de Física Gleb Wataghin, Universidad Estadual de Campinas (UNICAMP) Caixa Postal 6165, Campinas 13083-970, SP, Brasil
5 Instituto de Física, Universidad Católica de Valparaíso - Valparaíso, Chile
Accepted: 22 February 2002
A two-dimensional magnetic particle in the presence of an external magnetic field is studied. Equilibrium thermodynamical properties are derived by evaluating analytically the partition function. When the external field is applied perpendicular to the anisotropy axis the system exhibits a second-order phase transition with order parameter being the magnetization parallel to the field. In this case the system is isomorph to a mechanical system consisting of a particle moving without friction in a circle rotating about its vertical diameter. Contrary to a paramagnetic particle, equilibrium magnetization shows a maximum at finite temperature. It is also shown that uniaxial anisotropy in a system of noninteracting particles can be misinterpreted as a ferromagnetic or antiferromagnetic coupling among magnetic particles, depending on the angle between the anisotropy axes and magnetic field.
PACS: 75.10.-b – General theory and models of magnetic ordering / 75.30.Gw – Magnetic anisotropy / 75.50.Tt – Fine-particle systems; nanocrystalline materials
© EDP Sciences, 2002
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