Evidence for a Pressure-Induced Magnetic-Nonmagnetic Transition of Pr Impurities in La

The depression of the superconducting transition temperature of lanthanum due to the presence of praseodymium impurities shows a pronounced maximum as a function of pressure at ≃230 kbar. We conclude that the $4f^2$ shell of Pr delocalizes under such high pressure and hence demagnetizes in analogy to the familiar case of the $4f^1$ configuration of Ce impurities in La at low pressure.