Thermal Fluctuations In A Titanomagnetite Mineral: A Two-Level Subsystem Approach

We present measurements of the field and temperature dependences of the relaxation of the magnetic moment of a magnetic mineral consisting of nanodimensional particles of titanomagnetite Fe3-xTixO4, with x congruent to 0.1, embedded in a volcanic glass, over an observation time window of 10 s <= t <= 10(4) s, following recoil from a positive saturating field to negative holding fields in the vicinity of the coercive field. The relaxation data are analyzed within the framework of a model which decomposes the free energy landscape into an ensemble of double well potentials, and the thermal fluctuation field H-f for this system is shown to exhibit a maximum as a function of temperature. Numerical simulations of viscosity isotherms based on the double well formalism are presented, which show that this maximum is a natural feature of the formalism, related to the distribution of characteristic energies of the double wells, and thus does not contradict the assumption of Arrhenius relaxation dynamics based on Maxwell-Boltzmann statistics. (C) 2006 American Institute of Physics.