Effect of localization of $5f$-electrons and pressure on magnetism in uranium intermetallics in spin-fluctuation theory

UCoGa and URhGa, two isostructural compounds, show opposite signs of the initial response of Curie temperature to applied hydrostatic pressure. To determine the physical origin of this difference the magnetization data measured with respect to temperature, magnetic field, and hydrostatic pressure were analyzed in the framework of the Takahashi spin-fluctuation theory. The parameters $T_0$ and $T_{\mathrm{A}}$ characterizing the distribution widths of the spin-fluctuation spectrum in the energy and wave-vector space, respectively, and $T_{\mathrm{C}}/T_0$, the degree of the $5f$-electron localization, have been determined. Examination of available experimental data for the other UTX ($T=\mathrm{a}$ transition metal, $X=\mathrm{Al}$, Ga) ferromagnets having the ZrNiAl-type structure revealed some correlations between the degree of the $5f$-electron localization represented by the spin-fluctuation parameters and the response of Curie temperature on the applied pressure. The extent to which this correlation can be used to describe the localization and magnetic behavior of other uranium ferromagnetic compounds is discussed.

Figure 1

Temperature dependence of the magnetization of UCoGa at different pressures, in an applied field of 0.1 T.

Figure 2

Temperature dependence of the magnetization of URhGa at different pressures, in an applied field of 0.1 T.

Figure 3

Magnetization curves of UCoGa and URhGa measured at 1.8 K in magnetic fields applied along the $c$ axis at various pressures with contribution from pressure cell already subtracted. The contribution from the pressure cell was determined by comparing data in 0 GPa and ambient pressure. Lines are used as a guide to the eye.

Figure 4

The Arrot plots of magnetization isotherm data UCoGa and URhGa measured at different pressures.

Figure 5

Pressure dependence of degree of localization, $T_{\mathrm{C}}/T_0$, for UCoGa and URhGa.