Weak magnetic transitions in pyrochlore Bi2Ir2O7

TL;DR

This study reveals a weak magnetic transition in Bi2Ir2O7 at 1.84 K with exceptionally small magnetic moments and persistent dynamics, indicating a novel magnetic state distinct from other pyrochlore iridates.

Contribution

It provides the first muon spin relaxation evidence of weak magnetic ordering and a second transition in Bi2Ir2O7, highlighting its unique magnetic properties.

Findings

Magnetic transition at 1.84 K with small magnetic moments

Weak magnetic field of 0.7 mT at low temperature

Second transition at 0.23 K with increased relaxation rate

Abstract

Muon spin relaxation measurements on Bi2Ir2O7 show that it undergoes a bulk magnetic transition at 1.84(3) K. This is accompanied by increases in the muon spin relaxation rate and the amplitude of the non-relaxing part of the signal. The magnetic field experienced by muons is estimated to be 0.7 mT at low-temperature, around two orders of magnitude smaller than that in other pyrochlore iridates. These results suggest that the low-temperature state represents ordering of exceptionally small magnetic moments with persistent weak dynamics. The relaxation rate increases further below 0.23(4) K, coincident with a growth in the specific heat, suggesting the existence of a second low-temperature magnetic transition.