Magnetic pressure dependence

Uranium metal is weaMy paramagnetic, with a magnetic susceptibility of 1.740 X 10 A/g at 20°C, and 1.804 x 10 A/g (A = 10 emu) at 350°C (51). Uranium is a relatively poor electrical conductor. Superconductivity has been observed in a-uranium, with the value of the superconducting temperature, being pressure-dependent. This was shown to be a result of the fact that there are actually three transformations within a-uranium (37,52). 

Fig. 5.10. The pressure dependence of saturation magnetization for iron-nickel alloys shows a strong pressure dependence in the neighborhood of the Invar alloys (28.5 to 40-at. % nickel in the fee phase). The shock data shown are in excellent agreement with the static high pressure data (after Wayne [69W01]).

The physical description of strongly pressure dependent magnetic properties is the object of considerable study. Edwards and Bartel [74E01] have performed the more recent physical evaluation of strong pressure and composition dependence of magnetization in their work on cobalt and manganese substituted invars. Their work contrasts models based on a localized-electron model with a modified Zener model in which both localized- and itinerant-electron effects are incorporated in a unified model. Their work favors the latter model. 

In a solution where a nonzero volume change between the electronic isomers, HS and LS, is encountered, the position of the spin equilibrium will depend on pressure. The volume change, usually denoted here AF°, may be obtained from the study of the pressure dependence of equilibrium properties such as the magnetic susceptibility or the electronic spectrum. In favorable cases, A F° values may be derived from the amplitude of sound absorption observed in ultrasonic relaxation measurements of a spin equilibrium as will be shown in the... 

Results obtained from the alkali iodides on the isomer shift, the NMR chemical shift and its pressure dependence, and dynamic quadrupole coupling are compared. These results are discussed in terms of shielding by the 5p electrons and of Lbwdins technique of symmetrical orthogonalization which takes into account the distortion of the free ion functions by overlap. The recoilless fractions for all the alkali iodides are approximately constant at 80°K. Recent results include hybridization effects inferred from the isomer shifts of the iodates and the periodates, magnetic and electric quadrupole hyperfine splittings, and results obtained from molecular iodine and other iodine compounds. The properties of the 57.6-k.e.v. transition of 1 and the 27.7-k.e.v. transition of 1 are compared. 

The Stoner product of UN (see Chaps. A and D) is greater than one, in agreement with the antiferromagnetic behaviour of this solid. The antiferromagnetism was attributed to itinerant band magnetism (as in some d-metals and compounds but unlike light actinide metals). In fact, cohesive properties of this solid have been well explained in a pure spin-polarised picture and Fournier et al. have shown that the magnetic uranium sublattice moment and the Neel temperature have a similar pressure dependence. Discrepancies existed, however, between calculations and experiments ... 

Since the application of pressure may modify strongly the charge density distribution in a solid, and therefore affects the orbital more than the spin moment, magnetic form factors and magnetic anisotropy may become much more pressure-dependent than usually assumed. 

Magnetic resonance studies have been performed in a number of different materials. In most cases the pressure dependence of the spin-Hamiltonian crystal-field parameters have... 

The kinetic effect on (1/72—1/7)) is proportional to (Amagnetic field as shown in Fig. 7.23. From the temperature and pressure dependence, the kinetic parameters presented in Table 7.13 were obtained. The two activation parameters, namely the entropy and the volumes of activation, are negative and also are of the same magnitude for all the lanthanide ions. These activation parameters imply a common water exchange mechanism for all the lanthanides studied and possibly an associative activation path of exchange. The activation volume, AV of —6.0 cm3 mol-1 probably reflects the difference between a large negative contribution due to the transfer of a water molecule electrostricted in the second coordination sphere to the first coordination sphere and a positive contribution due to the difference in partial molar volumes of N + 1 coordinated transition state and N coordinated aquo lanthanide ion. It should be noted that the latter difference (in partial molar volumes of Fn(H20)w+i and Fn(H20)jv is due to the increase in Fn-O bond distance (Fig. 7.16). 

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