Magnetic field dependence of the neutron spin resonance in CeB6

TL;DR

This study investigates how magnetic fields influence spin excitations in CeB6, revealing a unique ferromagnetic resonance behavior in a heavy-fermion metal through inelastic neutron scattering and ESR measurements.

Contribution

It provides the first detailed analysis of magnetic field effects on spin fluctuations in CeB6, highlighting the coexistence of ESR and INS observations of ferromagnetic resonance.

Findings

No field splitting of the exciton peak in CeB6.

Observation of a second field-induced magnon with increasing energy.

Reappearance of a single mode at the ferromagnetic zone center at higher fields.

Abstract

In zero magnetic field, the famous neutron spin resonance in the f-electron superconductor CeCoIn5 is similar to the recently discovered exciton peak in the non-superconducting CeB6. Magnetic field splits the resonance in CeCoIn5 into two components, indicating that it is a doublet. Here we employ inelastic neutron scattering (INS) to scrutinize the field dependence of spin fluctuations in CeB6. The exciton shows a markedly different behavior without any field splitting. Instead, we observe a second field-induced magnon whose energy increases with field. At the ferromagnetic zone center, however, we find only a single mode with a non-monotonic field dependence. At low fields, it is initially suppressed to zero together with the antiferromagnetic order parameter, but then reappears at higher fields inside the hidden-order phase, following the energy of an electron spin resonance (ESR). This is a unique example of a ferromagnetic resonance in a heavy-fermion metal seen by both ESR and INS consistently over a broad range of magnetic fields.