Resonance-Like Magnetic Excitations in Spinel Ferrimagnets FeCr_2O_4 and NiCr_2O_4 Observed by Neutron Scattering(Condensed matter: electronic structure and electrical, magnetic, and optical properties)

概要

論文の詳細を見る
We performed powder neutron scattering experiments on spinel ferrimagnets ACr_2O_4 with magnetic and Jahn-Teller A^<2+> ions (A=Fe, Ni, Cu). In both FeCr_2O_4 and NiCr_2O_4, although geometric frustration had been expected to vanish so far, resonance-like magnetic excitation modes were discovered around Q≃1.4Å^<-1> and E≃5 and 8 to 9meV in a low-temperature magnetic order phase, similar to the local spin resonance modes early reported in highly frustrated spinel antiferromagnets ACr_2O_4 with nonmagnetic and non-Jahn-Teller A^<2+> ions (A=Mg, Zn). In a high-temperature magnetic order phase the resonance-like inelastic scattering transformed into quasielastic scattering. In CuCr_2_O4 no such diffusive scattering was observed. We interpret the resonance-like magnetic excitations as a dynamical spin-frustration effect, and discuss a necessary condition for the appearance of them.
2008-12-15