High resolution measurements of the de Haas–van Alphen frequency associated with the minority-spin electron 'lens' sheets of the Fermi surface of iron have been carried out between 1 and 4.2 K. The variation of the frequency over this temperature range is found to be less than one part in 105 (the resolution of our experiment) and is virtually identical to that found for the corresponding electron lenses in molybdenum. By contrast, a variation of one part in 104 would be expected for the Fe lenses on the basis of a literal interpretation of the Stoner model, in which the exchange splitting of the energy bands is proportional to the magnetization at all temperatures. The absence of any significant change of the frequency with temperature can be understood if the magnetization decreases almost entirely by spin wave excitations, and if the spin waves have negligible effect on the exchange splitting.

Lonzarich, G., & Gold, A. V. (1974). Temperature Dependence of the Exchange Splitting in Ferromagnetic Metals I. Information from the de Haas–van Alphen Effect in Iron. Canadian Journal of Physics, 52(8), 694–703.