Emergence of Tetrahedral Magnetic Order in Ultrathin Pyrochlore Iridate Films

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Journal Article



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We report on thickness-dependent magnetotransport in (111)-oriented Pb2Ir2O7–x (Pb227) epitaxial thin films. For thicknesses greater than 4 nm, the magnetoresistance (MR) of metallic Pb227 is positive, linear and non-saturated up to 14 T. However, at 4 nm, the conduction turns nonmetallic and the MR becomes negative and asymmetric upon field-cooling; such traits are reminiscent of all-in-all-out (AIAO) magnetic order in the insulating pyrochlore iridates. Low-field magnetic hysteresis and field-cooled resistivity bifurcations indicate the presence of magnetic, conducting domain walls. In addition to AIAO order, field-orientation-dependent MR suggests a magnetic phase space hosting 2-in-2-out "spin ice" order. Such anomalous magnetotransport calls for reevaluation of the pyrochlore iridate phase diagram, as the metallic end-members do not simply lie in a paramagnetic regime when subject to epitaxial constraints; in fact, strained ultrathin Pb227 exhibits traits reminiscent of both the insulating magnetic and metallic spin-liquid members.

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