Magnetic excitations in NdAl2

Abstract

The magnetic excitation spectrum of the ferromagnet Nd${\mathrm{Al}}_2$ has been studied at 4.2 K by neutron inelastic scattering. Three acoustical, three optical branches, and partly a fourth optical branch have been resolved. Crystal-field and exchange parameters have been obtained by analyzing the results in terms of a pseudoboson theory that includes all ten levels of the free-ion ground state of ${\mathrm{Nd}}^{3+}$. A good description of the observed excitation energies and intensities is obtained. The reliability of the model parameters is supported by internal consistency checks and by comparison with various physical properties of Nd${\mathrm{Al}}_2$. The interatomic exchange parameters exhibit a Ruderman-Kittel-Kasuya-Yosida-like qualitative behavior.