Actinide magnetic susceptibility

An approach other than steric hindrance has been used to overcome the previously mentioned instability of the actinide homoalkyls. It was found that the inclusion of jT-bonding ligands in the coordination sphere considerably enhanced the stability of the alkyl complex. Recently, the same line of reasoning has also yielded a new series of 7r-cyclopentadienyl lanthanide alkyls (C5H5)2LnR where Ln =Gd, Er, Yb and R = C=C, and CH3 120,121). The infrared data for these complexes are consistent with u-bonded structures and the room temperature magnetic susceptibilities are very close to the free ion values. The actinide complexes (75,... 

For solids in which IN([Xf) is very near to 1, often, although no magnetic order occurs, long-range fluctuations of coupled spins may take place, giving particular form to properties such as the (Stoner enhanced) magnetic susceptibility x, the electrical resistivity, and the specific heat of the solid. Spin fluctuations have been observed in actinides, and will be discussed in more detail in Chap. D. 

Table 3. Density of states at the Fenni level for actinide metals from band calculations (model) from the electronic contribution y to the specific heat from magnetic susceptibility measurements. The increasing values indicate a decreasing 5 f bandwidth pinned at Ep for americium metal (not shown) there is a sudden decrease in N(np)...

Magnetic susceptibility measurements are basic to the study of the magnetic properties of a compound samples under powder form are sufficient to start with and, what is very important in the case of actinides, small amounts of material are satisfactory (typically 100 mg). When working with transuranium compounds, safety requirements are fulfilled by working with sealed containers ... 

The interaction of the actinides or of their hydrides with chalcogens or H2X, respectively, give a number of nonstoichiometric phases with a composition close to AnX, An2X3, A11X2, An2Xs, or A11X3. Their thermal stability decreases in the order S > Se > Te. The magnetic susceptibility and Mossbauer spectroscopy show that the latter compounds may be formulated as [An +]2(S )2(S-Sf-, [An +]2(S -)3(S-S)2-, and [An +](S2-)(S-S)2-. These compounds have coordination numbers of 8, 10, and... 

Basic characteristics of actinide metals. X300K s the magnetic susceptibility at T— 300 K jiet( and 6p the Curie-Weiss parameters Tc N the temperature of magnetic ordering y the linear coefficient of... 

In this section we describe how the specific heat, magnetic susceptibility and electrical resistivity of anomalous lanthanide and actinide intermetallics respond to applied pressure. Generally each subsection is organized by material type first Ce-based compounds, then those based on Yb and finally U-based systems. Only in the last subsection on semiconductors are these systematics broken. Although on occasions we digress into a brief discussion of the experimental observations, ihe bulk of critical discussion related to data presented here and in sect. 3 is reserved for sect. 4. 

We have focused on two issues (1) the degree to which the pressure response of the electrical resistivity, magnetic susceptibility and specific heat is similar in a given material or class of materials and how this pressure dependence is related to the Griineisen parameter obtained from ambient pressure measurements and (2) the extent to which this comparison holds in both anomalous lanthanide and actinide compounds. 

Fig. 42. The magnetic susceptibility per lanthanide or actinide atom as a function of temperature, as predicted by the electronic polaron model. The susceptibility is in units of /iln/ri, where the effecitve moment includes the orbital contribution, as discussed in Liu (1988).

---