Orthogonal magnetization and symmetry breaking in pyrochlore iridate Eu2Ir2O7

Abstract

Electrons in the pyrochlore 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 Eu₂Ir₂O₇ shows a metal-insulator transition at T[subscript N] 1/4 120 K below which a magnetically ordered state develops. Using torque magnetometry, we uncover an unusual magnetic response. A magnetic field H applied in its a-b plane produces a nonlinear magnetization M⊥ orthogonal to the plane. M⊥ 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. 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[subscript N], suggestive of an additional order parameter 𝞰 already present at 300 K.