Entropy-stabilized materials as a platform to explore terbium-based pyrochlore frustrated magnets

Abstract

Two decades of work have shown that the physics of Tb-based pyrochlores is controlled by a subtle equilibrium between quadrupole-quadrupole and dipolar-dipolar magnetic interactions, as exemplified by the ordered spin ice Tb2Sn2O7 and the quantum spin liquid candidate Tb2Ti2O7. The high-entropy approach is thus quite promising, as it offers the possibility of a delicate tuning of chemical disorder. In this work, we investigate the entropy-stabilized pyrochlore compound Tb2(TiZrHfGeSn)2O7. We report the lack of long range magnetic order, yet the observed magnetic diffuse scattering is characteristic of antiferromagnetic first-neighbor correlations. The crystal field excitation spectrum, with broaden levels, visibly reflects the smooth environmental disorder of the Tb environment. The low energy dynamics are characterized by a narrow mode at about 0.4 meV, consistent with specific heat. Remarkably, as illustrated by a model of random isotropic shifts of oxygen atoms around Tb ions, the spectral weight of this mode is a direct consequence of deviations from the D3d symmetry at Tb sites. In the light of these results, quadrupolar interactions are also discussed. Frustrated magnetic systems such as pyrochlores are interesting for the complexity of their competing low-temperature phases. Here, the intrinsic disorder of the entropy-stabilized compound Tb2(TiZrHfGeSn)2O7 is utilized to investigate the elusive ground state of Tb-based pyrochlore magnets.