Gap in the magnetic excitation spectrum of Ce3Bi4Pt3

Abstract

Static-susceptibility and thermal-expansion measurements indicate that ${\mathrm{Ce}}_3$ ${\mathrm{Bi}}_4$ ${\mathrm{Pt}}_3$ is mixed-valent-like, whereas transport measurements reveal a gap of Δ=5 meV in the electronic excitation spectrum. We report the magnetic response of ${\mathrm{Ce}}_3$ ${\mathrm{Bi}}_4$ ${\mathrm{Pt}}_3$, at temperatures between 2 and 150 K, determined with incident neutron energies of 3.1, 17, and 69 meV. The isostructural, nonmagnetic reference compound ${\mathrm{La}}_3$ ${\mathrm{Bi}}_4$ ${\mathrm{Pt}}_3$ was also studied at the same temperatures and energies so that phonon contributions could be subtracted accurately. At 2 K, a gap ${\mathrm{\Delta }}_{\mathit{m}}$=12 meV is present in the magnetic excitation spectrum: the 3.1-, 17-, and 69-meV data consistently show that the magnetic intensity is zero for energy transfers less than 12 meV, rises sharply between 12 and 20 meV, and falls off smoothly beyond. Above 50 K, the gap in the spin-spin correlation function starts to fill. The neutron results reproduce the temperature dependence of the bulk susceptibility. The relationship between these and other measurements will be discussed.