THEORY OF PRESSURE EFFECTS AND THE CORRELATED-ELECTRON BEHAVIOR OF URANIUM MONOCHALCOGENIDES

Experimentally, hydrostatic pressure experiments provide a very sensit ive way to probe the development of magnetic ordering in correlated-el ectron systems. The recent high pressure experiments of Link et al. on UTe provide extremely interesting results. With applied pressure, the Curie temperature T-C for UTe increases from 104 K to a maximum of 18 1 K at 7.5 GPa and then decreases to 156 K at 17.5 GPa. This experimen tal behavior is qualitatively what we expect on the basis of our theor y of the correlated-electron behavior. Basically, increasing pressure causes increased hybridization which causes an increase in coupling be tween the moments associated with the relatively localized part of the f spectra density at each lattice site. However, as the pressure incr eases further, the loss of localized f spectra density caused by the i ncreased merger with the non-f-band density causes a decrease in order ed moment and hence a decrease in T-C. We have performed calculations quantifying the above picture for UTe. First we calculate the pressure dependence of the lattice constant and obtain good agreement with the experiment. Next, at calculated lattice constants we calculated T-C u sing our correlated-electron theory for magnetic ordering. These resul ts capture the initial increase in T-C resulting from increased hybrid ization as well as the reversal of this initial increase caused by the loss of localized f density.