Pressure Dependence of the Magnetic Transition Temperatures in Terbium from Resistance Measurements

The pressure coefficient of the Curie and Néel temperatures, $T_{\mathrm{cf}}$ and $T_N$, are determined using electricalresistance $R$ measurements. The resistance of polycrystalline terbium at constant pressure is determined over the temperature range 200 to 400°K. Pressures to 14.22 kbar are employed. Resistance measurements were made using the standard four-probe method. The Curie and Néel temperatures are determined from (1) plots of $R$ versus $T$ and (2) plots of $\frac{\mathrm{dR}}{\mathrm{dT}}$ versus $T$. The values of $T_{\mathrm{cf}}$ and $T_N$ thus obtained agree to within ±1°K. The pressure coefficient of the Néel temperature is found to be -1.05°K/kbar; while the coefficient for the ferromagnetic Curie point is determined at -1.24K°/kbar. The variation of the ratio of the Néel temperature to the de Gennes factor, $T_N{\mathrm{}(g-1\mathrm{})\mathrm{}}^{2}J(J+1\mathrm{})\mathrm{}$, with pressure is discussed in terms of the variation of the shape of the Brillouin zone, the number of energy states per atom, and the density of states per energy level in the zone with pressure which is directly related to the variation of the $\frac{c}{a}$ ratio with pressure.