1ST AND 2ND ORDER TRANSITIONS IN SOME METALLIC FERROMAGNETS

Second order transitions are discussed for compounds of the heavy rare earths and yttrium with cobalt. The calculated Curie temperatures agree well with those observed and an analogy is established between the effect of rare earth additions and of pressure. First order transitions in critical fields and at critical temperatures occur in some of these compounds. The effects of magnetoelasticity on such transitions are investigated by reformulating the Bean-Rodbell theory of 1962 in itinerant electron terms. It is found that in general these effects are smaller than those arising from the itinerant electron character itself, meaning the temperature dependence of the Landau coefficient B of M4 which is completely different from the Bean-Rodbell case.