Correlations of the Nd Magnetic Moments and Their Influence on the Specific Heat inNd2−xCexCuO4

Abstract

We study the effect of Ce substitution on the magnetic excitations of Nd in ${\mathrm{Nd}}_{2\ensuremath{-}x}{\mathrm{Ce}}_{x}{\mathrm{CuO}}_{4}$ by inelastic neutron scattering. A strong softening of the spin waves upon doping is observed, due to a decrease of the Cu-Nd exchange field at the Nd site. Consequently, a high spin-wave density of states is created at low energies, which leads to giant $\ensuremath{\gamma}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}C/T$ values at low temperatures. This demonstrates that the magnetism of the Nd ions is the only source of the large $\ensuremath{\gamma}$ values found in specific-heat experiments, i.e., ${\mathrm{Nd}}_{2\ensuremath{-}x}{\mathrm{Ce}}_{x}{\mathrm{CuO}}_{4}$ has to be excluded as a prototype of a novel heavy-fermion system.