Strong quantum fluctuations due to competition between magnetic phases in a pyrochlore iridate

TL;DR

This study investigates magnetic structures in pyrochlore iridates Yb2Ir2O7 and Lu2Ir2O7, revealing strong quantum fluctuations and phase competition effects that suppress magnetic moments, especially in Yb2Ir2O7.

Contribution

It provides neutron diffraction evidence of magnetic structures and highlights the role of phase competition in quantum fluctuations within pyrochlore iridates.

Findings

Both compounds exhibit all-in-all-out magnetic order below 150 K.

Yb2Ir2O7 shows suppressed Yb moments due to phase competition.

Reduced Yb moments are linked to coupling with Ir magnetic order.

Abstract

We report neutron diffraction measurements of the magnetic structures in two pyrochlore iridates, Yb2Ir2O7 and Lu2Ir2O7. Both samples exhibit the all-in-all-out magnetic structure on the Ir4+ sites below TN~ 150,K, with a low temperature moment of around 0.45 muB/Ir. Below 2\,K, the Yb moments in Yb2Ir2O7 begin to order ferromagnetically. However, even at 40 mK the ordered moment is only 0.57(3)muB/Yb, well below the saturated moment of the ground state doublet of Yb3+ (1.9 muB/Yb), deduced from magnetization measurements and from a refined model of the crystal field environment, and also significantly smaller than the ordered moment of Yb in Yb2Ti2O7 (0.9 muB/Yb). A mean-field analysis shows that the reduced moment on Yb is a consequence of enhanced phase competition caused by coupling to the all-in-all-out magnetic order on the Ir sublattice.