Itinerant magnetic state

As shall be discussed in sections 4 and 5, the change in electronic structure properties under the application of external pressure gives important information. It may lead to novel phenomena and in addition the volume dependence is a crucial parameter in testing theoretical models. For example, certain intermetallics may be driven from a localized to an itinerant magnetic state with reduced volume. Mdssbauer spectroscopy is well suited for such studies. 

NpOs2 this intermetallic Laves phase is ferromagnetic below T = 7.5 K with p d = 0.4 Pb while p ff = 3.3 Pb - The magnetie entropy is 0.2 RLn2 while y = 205 mJ/mol j 238) y dditional evidence for itinerant magnetism comes from the very large superimposed susceptibility in the ordered state... 

I shows a magnetic moment of 2.71 between 100 and 300 K. Since there is no specific short contact between the molecules, there is no ferromagnetic interaction in the solid state. Among the nonmetallic molecular magnets known, Cgo TDAE where TDAE = (Mc2N)2 C=C(NMe)2, which orders into an itinerant ferromagnetic state with a of... 

For a deeper discussion of the subject, I refer to a book by Yosida [127] and, for itinerant magnetism and general solid state physics with any relation to magnetism, a book by Kiibler [128]. 

In order to test the 5f origin of the magnetic moments in UTX ternaries and to follow the transition from the itinerant non-magnetic state to a more localized state with magnetic ordering several pseudo-ternary series were studied. 

When spin-fluctuation effects are taken into account, the state can no longer be regarded as magnetically uniform. Instead of the free energy mentioned in eq. (8) for an itinerant magnet, we must now study the free energy density per unit volume A/(r), which is given as (Shimizu 1981, Yamada 1991, 1993)... 

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... 

In the Introduction the problem of construction of a theoretical model of the metal surface was briefly discussed. If a model that would permit the theoretical description of the chemisorption complex is to be constructed, one must decide which type of the theoretical description of the metal should be used. Two basic approaches exist in the theory of transition metals (48). The first one is based on the assumption that the d-elec-trons are localized either on atoms or in bonds (which is particularly attractive for the discussion of the surface problems). The other is the itinerant approach, based on the collective model of metals (which was particularly successful in explaining the bulk properties of metals). The choice between these two is not easy. Even in contemporary solid state literature the possibility of d-electron localization is still being discussed (49-51). Examples can be found in the literature that discuss the following problems high cohesion energy of transition metals (52), their crystallographic structure (53), magnetic moments of the constituent atoms in alloys (54), optical and photoemission properties (48, 49), and plasma oscillation losses (55). 

The Stoner model, which we discuss in its simplest form, describes the formation of a net magnetic moment for itinerant electrons in a narrow band by adding to the basic Hamiltonian (11) of band theory a perturbing term accounting for total energy increase in case the itinerant electrons spins are not polarized (as in an atom for states not maximizing the spin). 

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