PRESSURE-DEPENDENCE OF MAGNETIC-ORDERING IN CORRELATED-ELECTRON MATERIALS

Magnetic ordering response to hydrostatic pressure provides a sensitiv e experimental probe of correlated-electron behavior. A striking featu re is that the ordering temperature may be relatively insensitive or e ven rise initially with pressure, while the ordered moment decreases o r indeed plunges dramatically. We will show that this is expected as t he f spectral density distribution in space and time is driven by incr eased band-f hybridization, and that this picture can be quantified us ing the theoretical framework we have developed for the diminution of ordered moment in highly correlated systems. We validate this theory b y detailed calculation for the ferromagnet UTe where Link et al. have shown that T(c) increases from 104 K to a maximum of 181 K at 7.5 GPa and then decreases to 156 K at 17.5 GPa. Our calculations (1) match th e experimental lattice change with pressure within 2% and provide the decrease in average 5f electron number, (2) calculate the increase in two-ion coupling with pressure (from increased f spectral admixture in to the bands) giving the initial increase in T(c), (3) calculate the d ecrease in ordering temperature (in terms of coupling) with decreased 5f number (decreased localized 5f spectral density giving ordered mome nt) which gives the ultimate decrease in T(c). The influence of the lo ss of localized f spectral weight on magnetic ordering is simulated by an Ising model with holes, where the LDA-calculated number of holes i ncreases with pressure, and each site fluctuates between being occupie d by a moment or empty.