OPTICAL PROPERTIES OF NICKEL ABOVE AND BELOW CURIE TEMPERATURE

The temperature dependence of the optical absorption spectrum of nickel has been measured over the wavelength range of 0·21-2·7 μm by means of Drude's method up to 500°K in ultra-high vacuum. The following characteristics were found: (i) a small bump near 1·4 ev which nearly disappears above the Curie temperature, whose energy is unchanged with temperature; (ii) a large absorption peak centred at about 5 ev. The peak position decreases linearly with temperature at a rate of 4·4 × 10-4 ev°K-1. The width of this peak decreases with increasing temperature up to the Curie temperature. The change in width is interpreted in terms of exchange splitting of the bands. We assign the low energy (1·4 ev) bump to the transition between the bands near the W and K symmetry points and the main peak (similar 5 ev) to the transition from L 2prime to L1 upper.