Influence of the demagnetization on the polarization of the thermal radiation emitted by hot cobalt wires

Abstract The polarization P of thermal radiation emitted by a hot cobalt wire in the temperature range from T ≈ 400 . K up to melting is studied for the first time. The radiation is linearly polarized perpendicularly to the wire. P decreases from 30 % . just above room temperature down to 6.5 % near melting and is continuous across the martensitic hcp − fcc transition at T m ≈ 700 K and across the Curie point at T c ≈ 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 thermal demagnetization of the wire with magnetic domain size change.