Muon spin relaxation and inelastic neutron scattering investigations of all-in/all-out antiferromagnet Nd2Hf2O7

TL;DR

This study investigates the spin dynamics and crystal field states of Nd2Hf2O7, revealing persistent spin fluctuations and detailed crystal field excitations, advancing understanding of its magnetic properties in frustrated pyrochlore systems.

Contribution

It provides the first combined muSR and INS analysis of Nd2Hf2O7, elucidating its magnetic ordering, spin fluctuations, and crystal field states with detailed anisotropy and multiplet information.

Findings

Confirms long-range magnetic order with persistent spin fluctuations.

Identifies crystal electric field excitations and determines crystal field parameters.

Reveals strong Ising-type anisotropy and dipolar-octupolar ground state character.

Abstract

Nd2Hf2O7, belonging to the family of geometrically frustrated cubic rare earth pyrochlore oxides, was recently identified to order antiferromagnetically below T_N = 0.55 K with an all-in/all-out arrangement of Nd3+ moments, however with a much reduced ordered state moment. Herein we investigate the spin dynamics and crystal field states of Nd2Hf2O7 using muon spin relaxation (muSR) and inelastic neutron scattering (INS) measurements. Our muSR study confirms the long range magnetic ordering and shows evidence for coexisting persistent dynamic spin fluctuations deep inside the ordered state down to 42 mK. The INS data show the crytal electric field (CEF) excitations due to the transitions both within the ground state multiplet and to the first excited state multiplet. The INS data are analyzed by a model based on CEF and crystal field states are determined. Strong Ising-type anisotropy is inferred from the ground state wavefunction. The CEF parameters indicate the CEF-split Kramers doublet ground state of Nd3+ to be consistent with the dipolar-octupolar character.