Itinerant Ferromagnetic Materials

In the past the effort to improve the understanding of finite temperature magnetic properties has mainly concentrated on itinerant ferromagnetic materials like Fe, Co, and Ni. The theoretical starting point was the one-electron finite temperature band theory which is known under the name Stoner-theory [108, 109]. Within... 

Correspondingly, there exist (i) paramagnetic, (ii) weakly itinerant ferromagnetic, and (iii) strongly itinerant ferromagnetic materials. 

Our elucidation of the structure helps in the understanding of the ferromagnetism in this material. It was argued previously that TDAE-Cso is an itinerant ferromagnet that is, the unpaired spins are carried by delocalized electrons. We have measured the electron paramagnetic resonance signal in this material, and find a relatively low value for the g-factor, g = 2.0008. This implies that the open-shell species reside principally on the C. and to a lesser extent on the TDAE. 

Very weak itinerant ferromagnets, defined as materials for which the splitting in energy between the + and - bands is very small, are predicted to have a number of distinctive properties. In particular, the value of the ratio qc/q% should be much greater than unity and roughly inversely proportional to the Curie temperature (Rhodes and Wohlfarth 1963). Here qc is obtained from the observed paramagnetic susceptibility using the relationship... 

A considerable number of compounds are found to have a large value of this ratio and the number of those with Curie temperatures below 50 K with values approaching unity seems rather small (Moriya 1979, Wohlfarth 1977). A value considerably in excess of unity is usually taken to be a strong indication of the itinerant nature of the magnetic electrons in a material. Other predictions of the theory of weak ferromagnetism include ... 

UPt has been reported to order ferromagnetically (or maybe ferrimagnetically) below Tc = 27-30 K by several authors (Matthias et al. 1969, Huber et al. 1975, Franse et al. 1981). The most profound study of UPt (magnetic, electrical resistivity, specific heat and neutron diffraction measurements) was made by Frings and Franse (1985a). Itinerant character of the magnetism in UPt follows from a rather low value of the spontaneous magnetic moment [(0.4-0.45)jlib per formula unit as measured on polycrystalline material]. This picture is also supported by a small... 

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