a Systematic Study of Mixed Valent Behavior: Resistivity, Specific Heat and Magnetic Susceptibility of Cerium

The pseudo-binary alloy systems Ce(Rh(,1-x)Ru(,x))(,2) and Ce(Rh(,1-y)Pt(,y))(,2) with 0 (LESSTHEQ) x, y (LESSTHEQ) 1 have been studied. We have measured the room temperature lattice constant, the electrical resistivity from 1.4 to 300K (600K for some samples), the magnetic susceptibility from 2 to 300K and the specific heat from 1.1 to 25K. The same set of measurements has also been performed on the lanthanum-analog systems, La(Rh(,1-x)Ru(,x))(,2) and La(Rh(,1 -y)Pt(,y))(,2). The valence of the cerium ions was determined directly using L(,III) absorption. The quantities measured indicate that we can separate the whole alloying range from CePt(,2) to CeRh(,2) to CeRu(,2) in two regions: a trivalent region from CePt(,2) to Ce(Rh(,.5)Pt(,.5))(,2) and a mixed valent region from Ce(Rh(,.5)Pt(,.5))(,2) to CeRh(,2) to CeRu(,2). The entire mixed valence range is spanned as the rhodium concentration is varied. CeRh(,2) is mixed valent in agreement with previous results. Parameters calculated from the data are compared to the predictions of two mixed valence theories based on the single impurity degenerate Anderson Hamiltonian, namely the large-N expansion and Bethe-ansatz methods. The two theories are equivalent and are found in qualitative agreement with the data.