Anisotropic superparamagnetic states of an isolated ferromagnetic nanoparticle with uniaxial single-ion anisotropy

✍ Scribed by E. E. Kokorina; M. V. Medvedev

• Book ID: 104557867
• Publisher: John Wiley and Sons
• Year: 2006
• Tongue: English
• Weight: 224 KB
• Volume: 3
• Category: Article
• ISSN: 1862-6351
• DOI: 10.1002/pssc.200563112

✦ Synopsis

Abstract

A molecular field approximation which takes into account both the thermal Brownian rotation of the total magnetic moment of a ferromagnetic nanoparticle and thermal deviations of atomic magnetic moments from the direction of the total magnetic moment has been elaborated. It has been shown by the example of an uniaxial single‐ion anisotropy of the second order that the different types of anisotropic superparamagnetic states can arise in such a nanoparticle depending on relationship between the anisotropy parameter (D > 0 or D < 0) and the intraparticle ferromagnetic exchange one (I > 0). In particular, for the case of a relatively weak anisotropy the ellipsoidal superparamagnetic state, as it is called, appears when the vector of the total magnetic moments moves during its Brownian rotation over the surface of prolated (at D > 0 – the easy‐axis anisotropy) or oblated (at D < 0 – the easy‐plane anisotropy) ellipsoid of rotation. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)