Higher harmonics in planar Hall effect induced by cluster magnetic multipoles

Abstract

Antiferromagnetic (AFM) materials are attracting tremendous attention due to their spintronic applications and associated novel topological phenomena. However, detecting and identifying the spin configurations in AFM materials are quite challenging due to the absence of net magnetization. Herein, we report the practicality of utilizing the planar Hall effect (PHE) to detect and distinguish “cluster magnetic multipoles” in AFM Nd2Ir2O7 (NIO-227) fully strained films. By imposing compressive strain on the spin structure of NIO-227, we artificially induced cluster magnetic multipoles, namely dipoles and A2- and T1-octupoles. Importantly, under magnetic field rotation, each magnetic multipole exhibits distinctive harmonics of the PHE oscillation. Moreover, the planar Hall conductivity has a nonlinear magnetic field dependence, which can be attributed to the magnetic response of the cluster magnetic octupoles. Our work provides a strategy for identifying cluster magnetic multipoles in AFM systems and would promote octupole-based AFM spintronics.

Engineering structural homogeneity and magnetotransport in strained Nd2Ir2O7 films

“…The strained NIO-227 thin films were grown using the "repeated rapid high-T synthesis epitaxy (RRHSE)" method, which utilizes the ablation of two targets (NIO-227 and IrO 2 ) and rapid thermal annealing. 41,42 We observed that controlling the amount of IrO 2 ablation results in a homogeneous and strained NIO-227 film structure and an enhancement of AHE in the NIO-227 film. This enhancement of AHE in NIO-227 films can be attributed to a decrease in defects and structural inhomogeneity.…”

“…This distinct behavior of semimetallic NIO-227 films can be elucidated by the compressive strain effect. 41,42 According to previous studies 41,42 of strained NIO-227 films, the valence and conduction bands move and cross near the Fermi level due to compressive strain. Notably, the ρxx reaches its lowest at 90% IrO 2 ablation and slightly increases at 95% IrO 2 ablation.…”

“…25,26,30 A further increase in IrO 2 ablation from 75% to 90% leads to the appearance of "odd-numbered peaks" (111) and (333) in the XRD patterns of the films, indicating excellent crystallization of the pyrochlore phase. 41,42 The peaks in the XRD patterns of the films with 85% and 90% IrO 2 ablation indicate the growth of high-quality NIO-227 films. In addition, it is worth noting that the growth of strained NIO-227 films is sensitive to both oxygen pressure and annealing temperature.…”

“…The finite value of σxy AHE (H = 0 T) in NIO-227 film is known as the strain-induced nontrivial contribution of antiferromagnetic ordering (T 1 -octupole) to the Berry curvature. 41,42 The σxy AHE should follow a ∝ σxx 1.6 scaling relationship. Our films with NIO-227 structure (85%, 90%, and 95% IrO 2 ablation) fall on the σxy AHE ∝ σxx 1.6 relationship, whereas the films with defects (75% and 80% IrO 2 ablation) do not [Fig.…”