The effect of magnetic interactions on low temperature saturation remanence in fine magnetic particle systems

In studies of fine magnetic particle systems, saturation remanence is often measured during warming from liquid helium temperature in order to determine the distribution of blocking temperatures. These data have usually been treated as if they are unaffected by magnetic interactions. However, this treatment is often inconsistent with the experimental data. Furthermore, the thermal decay of saturation remanence often gives values for the mean blocking temperature that are inconsistent with other measurements, such as low temperature ac susceptibility and zero-field-cooled magnetization curves. As an alternative interpretation of these remanence data, we suggest that interactions destabilize the saturation remanence state and accelerate its decay with increasing temperature. As a result, the blocking temperatures associated with the thermal decay of remanence are effectively reduced. We have modeled the effects of interactions on low temperature saturation remanence data using a simple mean interaction field model. This model produces remanence curves that have a steep slope at low temperatures, consistent with experimental curves frequently reported in the literature. (C) 2000 American Institute of Physics. [S0021-8979(00)05713-3].