Fragile singlet ground state magnetism in pyrochlore osmates R2Os2O7 (R=Y and Ho)

TL;DR

This study investigates the fragile singlet ground state magnetism in pyrochlore osmates Y2Os2O7 and Ho2Os2O7, revealing a spin-glass state in the former and long-range magnetic order in the latter, highlighting the influence of weak 4f-5d interactions.

Contribution

It demonstrates the sensitivity of singlet ground state magnetism in R2Os2O7 to weak 4f-5d interactions, showing different magnetic ground states in Y and Ho variants.

Findings

Y2Os2O7 exhibits a spin-glass ground state below 4 K.

Ho2Os2O7 shows long-range magnetic order below 36 K.

Fragile singlet ground state can be disturbed by weak 4f-5d interactions.

Abstract

The singlet ground state magnetism in pyrochlore osmates Y$_2$Os$_2$O$_7$ and Ho$_2$Os$_2$O$_7$ is studied by DC and AC susceptibility, specific heat, and neutron powder diffraction measurements. Despite the expected non-magnetic singlet in the strong spin-orbit coupling (SOC) limit for Os$^{4+}$ ($5d^4$), Y$_2$Os$_2$O$_7$ exhibits a spin-glass (SG) ground state below 4 K with weak magnetism, suggesting possible proximity to a quantum phase transition between the non-magnetic state in the strong SOC limit and the magnetic state in the strong superexchange limit. Ho$_2$Os$_2$O$_7$ has the same structural distortion as occurs in Y$_2$Os$_2$O$_7$. However, the Os sublattice in Ho$_2$Os$_2$O$_7$ shows long-range magnetic ordering below 36\,K. The sharp difference of the magnetic ground state between Y$_2$Os$_2$O$_7$ and Ho$_2$Os$_2$O$_7$ signals the singlet ground state magnetism in $R_2$Os$_2$O$_7$ is fragile and can be disturbed by the weak $4f-5d$ interactions.