Evidence for a dynamical ground state in a frustrated pyrohafnate Tb2Hf2O7

TL;DR

This study provides evidence that Tb2Hf2O7 exhibits a dynamical ground state characterized by persistent spin fluctuations and no long-range magnetic order down to very low temperatures, indicating complex frustrated magnetism.

Contribution

The paper demonstrates the existence of a dynamical ground state in Tb2Hf2O7 through comprehensive magnetic and neutron scattering measurements, revealing slow spin dynamics and persistent fluctuations.

Findings

No long-range magnetic order down to 0.1 K

Presence of slow spin dynamics and persistent fluctuations

Dominant antiferromagnetic interactions

Abstract

We report the physical properties of Tb2Hf2O7 based on ac magnetic susceptibility \chi_ac(T), dc magnetic susceptibility \chi(T), isothermal magnetization M(H), and heat capacity C_p(T) measurements combined with muon spin relaxation (\muSR) and neutron powder diffraction measurements. No evidence for long-range magnetic order is found down to 0.1 K. However, \chi_ac(T) data present a frequency-dependent broad peak (near 0.9 K at 16 Hz) indicating slow spin dynamics. The slow spin dynamics is further evidenced from the \muSR data (characterized by a stretched exponential behavior) which show persistent spin fluctuations down to 0.3 K. The neutron powder diffraction data collected at 0.1 K show a broad peak of magnetic origin (diffuse scattering) but no magnetic Bragg peaks. The analysis of the diffuse scattering data reveals a dominant antiferromagnetic interaction in agreement with the negative Weiss temperature. The absence of long-range magnetic order and the presence of slow spin dynamics and persistent spin fluctuations together reflect a dynamical ground state in Tb2Hf2O7.