Orthogonal Magnetization and Symmetry Breaking in Pyrochlore Iridate Eu2Ir2O7

TL;DR

This study reveals unconventional magnetic responses in Eu2Ir2O7, showing orthogonal magnetization and symmetry breaking linked to octupolar order and possible additional order parameters, advancing understanding of pyrochlore iridates.

Contribution

It uncovers a nonlinear orthogonal magnetization and symmetry breaking in Eu2Ir2O7, indicating novel octupolar magnetic order and potential additional order parameters.

Findings

Observation of nonlinear orthogonal magnetization $M_ot$

Detection of $d$-wave field-angle pattern consistent with octupolar order

Sensitivity of $d$-wave pattern to field-cooling direction

Abstract

Electrons in the pyrochore iridates experience a large interaction energy in addition to a strong spin-orbit interaction. Both features make the iridates promising for realizing novel states such as the Topological Mott Insulator. The pyrochlore iridate Eu$_2$Ir$_2$O$_7$ shows a metal-insulator transition at $T_N \sim$ 120 K below which a magnetically ordered state develops. Using torque magnetometry, we uncover a highly unusual magnetic response. A magnetic field $\bf H$ applied in its $a$-$b$ plane produces a nonlinear magnetization $M_\perp$ orthogonal to the plane. $M_\perp$ displays a $d$-wave field-angle pattern consistent with octupolar order, with a handedness dictated by field cooling, leading to symmetry breaking of the chirality $\omega$. A surprise is that the lobe orientation of the $d$-wave pattern is sensitive to the direction of the field when the sample is field-cooled below $T_N$, suggestive of an additional order parameter $\eta$ already present at 300 K.