Rdsum6.-On expose une thdorie gdndrale des fluctuations de spins et les propriiStds thermodynamiques du magndtisme dlectronique itingrant, interpolation entre les limites faible et forte du ferromagndtisme. On donne une expression unifide de la tempdrature de Curie et on discute la signification physique de la susceptibilit6 magn6tique statique de Curie-Weiss. En tant que phdnomSnes nouveaux ddcoulant de cette thdorie, on discute les moments magndtiques locaux ddpendant de la tempdrature c o m e ceux observds dans CoS2, CoSez, etc. et les propridtds magnstiques et thermiques des semiconducteurs presque magndtiques connus de Si.Abstract.-A general theory of spin fluctuations and thermodynamical properties of itinerant electron magnets is developed, interpolating between the weakly and strongly ferromagnetic limits. A unified expression is given for the Curie temperature and the physical meaning of the Curie-Weiss magnetic susceptibility is discussed. As new phenomena derived from this theory the temperature-induced local magnetic moments as observed in CoSz, CoSe2, etc. and peculiar magnetic and thermal properties of nearly ferromagnetic semiconductors such as FeSi are discussed.
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