Susceptibilities and Negative Knight Shifts of Intermetallic Compounds

Knight shift measurements have recently been made on a series of compounds having the $\beta$-Wolfram structure ${\mathrm{V}}_{3}X$, namely ${\mathrm{V}}_3$As, ${\mathrm{V}}_3$Au, ${\mathrm{V}}_3$Ga, ${\mathrm{V}}_3$Ge, ${\mathrm{V}}_3$Pt, ${\mathrm{V}}_3$Sb, ${\mathrm{V}}_3$Si, and ${\mathrm{V}}_3$Sn. More recently susceptibilities have been measured on some of these compounds. It is observed that (a) materials with a high superconducting transition temperature show temperature-dependent Knight shifts and susceptibilities, (b) the vanadium shifts $K_{\mathrm{V}}$ are positive and decrease with decreasing temperature, and (c) the $X$-site shifts $K_X$ are negative and increase in magnitude with decreasing temperature. A simple model is offered which uses the exchange polarization mechanism to relate the sign and temperature dependence of $K_{\mathrm{V}}$ and $K_X$ to the temperature-dependent susceptibility.