Influence of irreversible demagnetization on the polarization of thermal radiation emitted by a hot cobalt wire

Abstract

We report measurements of the polarization P of thermal radiation emitted by a cobalt wire in the temperature range from T ≈ 400 K up to melting. The radiation is linearly polarized perpendicular to the wire. P decreases from 30 % just above room temperature down to 6.5 % near melting and does not show any particular behavior neither at the martensitic hcp−fcc transition at ≈ 700 K nor at the Curie point at ≈ 1400 K. However, P shows a rapid decrease for T 1000 K and, contrary to previous measurements with tungsten wires, it hysteretically behaves if the temperature change is reversed. This behavior is rationalized by accounting for the irreversible thermal demagnetization of the wire with magnetic domain size change.