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

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 Tm≈700 K and across the Curie point at Tc≈1400K. However, P shows a rapid decrease for T≳1000K 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.