Abstract: Dynamics of magnetic response of iron whiskers near the Curie point

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Abstract
Iron whiskers are used as the core of a transformer with concentric windings to find the magnetic frequency response near the Curie temperature Tc. In this review we emphasize the dynamics at high temperatures. We discuss the magnetic viscosity and the role of magnetic fluctuations using the phenomenology of magnetic memory functions. We have introduced a new memory function from which we extract evidence for critical slowing down. The time scale of critical slowing down, which becomes as low as 10−4 sec, is given by the response time of rapidly growing correlation clusters near Tc. For temperatures slightly below Tc (Tc−.3c−.03, the curling region) we apply equations we have developed to interpret the magnetic response of conducting soft magnetic materials. We are able to extract the intrinsic magnetic response. It is shown that in the curling region the role of the intrinsic damping is dominant and it is described by a temperature independent coefficient for the Gilbert damping. The measured loss in the curling region is higher (∼10×) than anticipated from resonance measurements. It is argued that this difference is caused by a large magnetization disorder in the curling region, contrary to resonance measurements where the disorder is small and all in the spin waves. The full paper will be submitted for publication elsewhere.

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