Dresden 2009 – scientific programme

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MA: Fachverband Magnetismus

MA 31: Magnetic Particles and Clusters I

MA 31.9: Talk

Thursday, March 26, 2009, 12:15–12:30, HSZ 401

Splitting of the Curie temperature for two-dimensional anisotropic nanoparticles — •Elena Y. Vedmedenko, Thim Stapelfeldt, and Roland Wiesendanger — University of Hamburg, Jungiusstr. 11, 20355 Hamburg

The Curie temperature Tc is defined as the critical temperature above which magnetization vanishes. For superparamagnets the magnetization vanishes at the so-called blocking temperature Tb < Tc. Therefore, the determination of the Curie point via measurements of the mean magnetization is often impossible. In another common procedure the Curie point is determined via the peak in the susceptibility and/or the peak in the specific heat, which should appear at the same characteristic temperature. We demonstrate by means of Monte-Carlo simulations that for two-dimensional superparamagnets with uniaxial anisotropy these two peaks appear at different, size-dependent characteristic temperatures Tc > Ts. At temperatures Tb < T < Tc such a particle is in the regime of thermally induced switching. The Néel-Brown switching mechanism is only possible below Ts. The attempt frequency of the switching via a domain wall is size- and form-dependent.