Local-moment magnetism

Within the general trend in the behavior across the actinide series, their alloys, and their metallic compounds from superconductors to local moment magnets, the only serious irregularity occurs in some plutonium compounds. These compounds should be magnetic but turn out to be temperature independent paramagnets. 

The problem could be stated from another point of view. In an isostructural series the uranium and neptunium compounds tend to be itinerant electron magnets or band magnets (like iron) and their orbital contribution is at least partially quenched. For much heavier actinides we know that the compounds will make local moment magnets with orbital contributions. It is quite possible that in between these two clear cut forms of magnetism that the intermediate case could be dominated by fluctuations, and no recognizable form of magnetism would occur. To state that the... 

Characteristics of some local-moment magnets T, lattice-Kondo temperature a-T , f-T , antiferromagnetic, ferromagnetic ordering temperatures y(2T ) and y(T—>0), Sommerfeld coefficients in the paramagnetic and magnetically ordered phases averaged ordered moment per f-ion,... 

The effect of pressure on the magnetism of Eu containing clathrates has been studied by means of electrical resistivity and Hall effect measurements [43, 48]. From pressure-dependent electrical resistivity measurements on type-I Eu2Ba6AlgSi36, Tc was shown to increase from 32.8 K at ambient pressure to 36.5 K at 16 kbar this was interpreted as evidence for local-moment magnetism [43]. In the RKKY picture this behavior suggests that pressure moves the system towards the extremum of the first (ferromagnetic) oscillation of /rkky-... 

Even though the macroscopic magnetization can be understood, we must not overlook the fact that the paramagnetic moment and the ordered moment are far from the values of the trivalent (or tetravalent) uranium ion. Lam and Ellis (1985) stress in a theoretical paper the importance of the hybridization of the 5f electrons with other electrons in the valence or conduction bands. Only if we accept that such an effect actually reduces the still more or less localized actinide moment are we entitled to use the terminology of localized-moment magnetism. 

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