Magnetic order, pressure dependence

In order to analyze the dynamic behavior of a magnetic head, time-dependent pressure should be calculated. This can be attained by solving the modified Reynolds equation including a squeezing term, i.e.. 

This table was derived from empirical data on conductivity and magnetism in solids. The shaded area maps the first order Mott transition between localised and itinerant behaviour in the solid, and the elements which lie on it have sensitive (e.g. pressure-dependent) properties. However, they are also remarkable in atomic physics for their giant resonances, are noted catalysts, or provide good materials for H storage, and then exhibit photon-stimulated desorption peaks which replicate the giant resonance profiles. Many of these properties seem to depend on the critical localisation of / and d electrons. 

We made some preliminary experiments on the pressure dependence of NHo production. At 25 e.v. it was nearly first order while at 16 e.v. it was closer to second order. We cannot say anything about magnetic field dependence. To explain the increase in radical yield observed at higher magnetic field (700 oe.), it is necessary to perform more elaborate calculations on the magnetic field dependence of the ion-molecule reactions (4 and 5). 

The thermal expansion behaviour in the magnetically ordered regime is closely connected with the pressure dependence of the Curie temperature. Measurements of Tc as a function of pressure were made on Nd2Fe14B by Fukamichi et al. (1986) and for several other R2Fe14B compounds by Kamarad et al. (1987) and Nagata et al. (1987). These authors showed that the Curie temperature of these compounds decrease strongly with applied pressure. By contrast, Kamarad et al. found that the spin reorientation temperature remains unaffected under pressure. 

The light lanthanides also exhibit some unusual electrical and magnetic properties. The superconductivity of lanthanum has already been mentioned. But when its behavior is compared to the superconductivity in scandium, yttrium and lutetium, we find lanthanum is unusual. The ordering temperature T, and pressure dependence of T are both larger in lanthanum than in the other three superconductors (see section 3.7.3 and fig. 12a). 

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