Magnetic phase transitions under pressure

The SmS semiconductor to metal transition was later verified by the direct observation of a discontinuous change in the optical reflectivity at 6 kbar (Kirk et al., 1972). This is consistent with a first order magnetic phase transition which was directly verified by magnetic susceptibility measurements under pressure by Maple and Wohlleben (1971). In the collapsed phase the susceptibility of SmS showed no magnetic order down to 0.35 iC and was almost identical to the susceptibility of SmBa (see fig. 20.10 of volume 2). Bader et al. (1973) measured the heat capacity (fig. 11.16) and electrical resistivity (fig. 11.17) of SmS under pressure. They found a large electronic contribution to the heat capacity ( y = 145 mJ/mole-K ) and a resistivity reminiscent of SmB. Mossbauer isomer shift measurements of SmS under pressure by Coey et al. (1976) reveal the transition from a Sm isomer shift at zero pressure to an intermediate value at pressures above 6 kbar (fig. 11.18). The isomer shift of SmS above 6 kbar was found to be about the same as the isomer shifts for chemically collapsed Smo.77Yo.23S and SmBo at zero pressure. 

Figure 95 shows the electrical resistivity p(T) for a- and c-axes as a function of temperature below 40 K under high pressures. At ambient pressure, the resistivity shows a sudden decrease near 35 K (=Tni). Moreover, the resistivity shows a small anomaly at 24 K (=Tn2)- The anomalies at and Tn2 correspond to the magnetic phase transitions which were mentioned before. The anomaly near Tni becomes less prominent with increasing pressure, corresponding to the pressure-induced decrease of the sublattice magnetization (Kawarazaki et al., 2000). Tni decreases with increasing pressure and disappears above 1.0 GPa ( Pci)-... 

Many authors have contributed to the study of die shift of magnetic phase transition temperatures under pressure in the heavy lanthanides and their alloys - see tables 1-3... 

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