Orthogonal Magnetization and Symmetry Breaking in Pyrochlore Iridate Eu2Ir2O7

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 $\mathbf{H}$ 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.

23 pages, 14 figures

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• Single-ion anisotropy in the gadolinium pyrochlores studied by an electron paramagnetic resonance
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