THE BARRIER PLOT AS A TOOL IN MAGNETIC-RELAXATION STUDIES

The analysis of magnetic relaxation in composites is greatly complicated by the great sensitivity of relaxation to the parameters that characterize the systems and the concomitant distribution of these parameters in any given sample. At the same time, the current interest in seeking evidence of quantum tunneling of magnetization has introduced an urgency for improving our ability to carry out an analysis of experimental results to such a degree of accuracy and reliability as to enable us to rule out classical processes as an explanation for any anomalous behavior. In this paper we present a refinement of the work of Street and Woolley and of Gaunt on magnetic relaxation in a fixed applied field. Our results center on the 'barrier plot', which is a surface plot of the distribution of energy barriers versus energy barrier and applied field. The barrier plot greatly facilitates analysis of experiments. We show, in particular, that some anomalous behavior of the magnetic viscosity can be understood in terms of purely classical thermal activation.