Actinide elements magnetic properties

Evidence other than that of ion-exchange favours the view of the new elements as an inner transition series. The magnetic properties of their ions are very similar to those of the lanthanides whatever range of oxidation states the actinides display, they always have -1-3 as one of them. Moreover, in the lanthanides, the element gado-... 

The transition metal ions generally have a number of d electrons in their outer shell, and because the energy difference between the various configurations is small, the arrangement adopted will depend upon a variety of external factors, such as the geometry of the crystal structure (see also Chapter 12 and Section S4.5). The lanthanides have an incomplete 4f shell of electrons, and the actinides an incomplete 5f shell. In these elements, the f orbitals are shielded from the effects of the surrounding crystal structure. The d and f electrons control many of the important optical and magnetic properties of solids. 

An additional problem a moveable muon might create is that its diflfusional path may lead to a lattice defect (most important are impurities and vacancies). Once reached, the muon is likely to be trapped and the pSR signal no longer relates to the bulk properties of the magnet. In rare-earth and actinide materials this is less of a problem than in transition element magnets where Tm tends to be high. 

Magnetic properties of actinide compounds with high content of transition element... 

It was already mentioned that only one binary compound of actinide metal ThMni2 is known, but its magnetic properties have not been reported. The ternaries are known to exist in a bulk crystalline form with Fe, Co and Ni as transition element and with Si, Mo and Re as stabilizing components. 

Although the outer electron configuration of the transition metals is not always the same within a group and there is often no regular pattern in the way the electron configuration changes from one metal to the next in the same period, all transition metals share many characteristics (multiple oxidation states, richly colored compounds, magnetic properties, and so on) that set them apart from other elements. These properties are similar because aU these metals have incompletely fiUed d subshells. Likewise, the lanthanide and actinide elements resemble one another because they have incompletely filled/subshells. 

Most textbooks discuss transition metal complexes separately from those of the main group elements. There is, in fact, much in common between the two classes and, whenever possible, we shall treat them as one. However, complexes of the transition metal ions may possess an incomplete shell of d electrons which necessitate separate discussion. This characteristic makes it particularly useful to determine the magnetic and spectral properties of members of this class of complexes and the exploration of these properties will require separate chapters devoted to them. In a similar way, complexes of the lanthanide and actinide elements, with, typically, an incomplete shell of f electrons tucked rather well inside the atom and away from the ligands—and so behaving rather as if they are in an isolated atom—require their own discussion. 

Although little use is made now of the theory presented in this chapter, it contains the basis of all of those that are used. It provides the foundation, particularly for the understanding of spectral and magnetic properties all else is elaboration and refinement. A knowledge of simple crystal field theory is therefore essential to an understanding of the key properties of transition metal complexes and particularly those covered in Chapters 8 and 9. This chapter deals exclusively with transition metal complexes. In one or more of their valence states, the ions of transition metals have their d orbitals incompletely filled with electrons. As a result, their complexes have characteristics not shared by complexes of the main group elements. It is the details of the description of these incompletely filled shells which is our present concern this is in contrast to the discussion of the previous chapter where the topic was scarcely addressed. Ions of the lanthanides and actinides elements have incompletely filled f orbitals and so necessitate a separate discussion which will be given in Chapter 11. 

Mossbauer spectroscopy is a powerful tool to gain essential information on the difference in electron structure between intermetallic compounds of 4f and 5f elements. In the latter series the work concentrates on Np materials. For this actinide bulk magnetic and transport data are still scarce and even neutron diffraction results are not plentiful. Mossbauer spectroscopy is thus in some sense a forerunner. It has been shown that measurements under high pressures are pivotal for a deeper insight of electronic properties, in particular with the question of 3d-like itinerant versus 4f-like localized electron behavior of the 5f electrons in Np. It becomes more and more apparent that U and Np behave often quite differently mainly because of the somewhat more pronounced tendency of the latter towards f localization. Nevertheless, the formation of 5f bands via hybridization plays a central role also in Np metallic compounds. 

In chapter 114, O. Vogt and K. Mattenberger examine the magnetic behaviors of the lanthanide and actinide Bl, NaCl-type structures. The magnetic properties of a sample depend upon the spectroscopic state of the f-element and the possibility of J-mixing, the electric crystalline field, the exchange interactions and hybridization. The competition between these various factors can make the materials complicated or simple with respect to their magnetic behaviors. 

The importance of Mossbauer spectroscopy in probing electronic structures of intermetallic compounds, especially those reflected in the magnetic properties, is discussed by W. Potzel, G.M. Kalvius and J. Gal (chapter 116). The authors have focused their discussions on selected samples where the differences between lanthanides and actinides can be best contracted. As the authors note, the two most interesting elements, at least with respect to anomalous f-electron behaviors, Ce and U, cannot be studied by Mossbauer spectroscopy because of the lack of a suitable isotope in the case of Ce, and just the experimental difficulty in getting Mossbauer spectra for U. 

The first edition consisted of a serial description of the individual actinide elements, with a single chapter devoted to the six heaviest elements (lawrendum, the heaviest actinide, was yet to be discovered). Less than 15 % of the text was devoted to a consideration of the systematics of the actinide elements. In this edition nearly half of the work consists of survey chapters in which such subjects as the metallic state, thermochemistry, solid state chemistry, solution chemistry, atomic and electronic spectroscopy, magnetic properties, organometallic chemistry, and the biological and environmental properties of the actinide elements are treated in comparative fashion. Because of the expansion of the discipline and of the scope of the second edition, many cdleagues were asked to contribute chapters that reflected their expert knowledge. 

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