Strain engineering of the magnetic multipole moments and anomalous Hall effect in pyrochlore iridate thin films

Abstract

The recent observation of the anomalous Hall effect (AHE) without notable magnetization in antiferromagnets has suggested that ferromagnetic ordering is not a necessary condition. Thus, recent theoretical studies have proposed that higher-rank magnetic multipoles formed by clusters of spins (cluster multipoles) can generate the AHE without magnetization. Despite such an intriguing proposal, controlling the unconventional AHE by inducing these cluster multipoles has not been investigated. Here, we demonstrate that strain can manipulate the hidden Berry curvature effect by inducing the higher-rank cluster multipoles in spin-orbit–coupled antiferromagnets. Observing the large AHE on fully strained antiferromagnetic Nd2Ir2O7 thin films, we prove that strain-induced cluster T1-octupoles are the only source of observed AHE. Our results provide a previously unidentified pathway for generating the unconventional AHE via strain-induced magnetic structures and establish a platform for exploring undiscovered topological phenomena via strain in correlated materials.

Correlated Magnetic Weyl Semimetal State in Strained Pr2Ir2O7

“…[1] This also explains the resistivity of Nd 2 Ir 2 O 7 (NIO) strained film becomes significantly enhanced compared to the bulk. [34] To further check the strain effect, sample with larger compressive strain was fabricated and it shows that larger strain leads to higher resistivity (Figure S6, Supporting Information), which is consistent with our above statement. However, the influence of the crystalline order or detects on the resistivity cannot be excluded completely.…”

“…The SHE observed in the PIO film indicates both cubic symmetry breaking and TRS breaking. [ 34 ] The cubic symmetry is broken by the compressive strain at the (111) plane, and the strain‐induced AIAO ordering breaks the TRS. It should be mentioned that the observed AHE in the PIO film is different from the conventional AHE in ferromagnetic materials where the anomalous Hall resistivity is proportional to its magnetization ( M ).…”

“…As demonstrated earlier in the magnetotransport results, the strained PIO film can have AIAO ordering. Then, in the pyrochlore lattice, a higher‐rank magnetic multipole, called the A 2 ‐octupole (ω xyz ) [ 34,54 ] can be formed by the clusters of spins. Even though AIAO ordering does not carry any dipole moments, an A 2 ‐octupole can induce the orthogonal magnetization M ⊥ when the magnetic field is applied.…”

“…[31][32][33] The resulting phase diagram is presented in Figure 1d, in terms of U and δ (the change ratio of the hopping parameter). Note that we use δ to simulate the strain effect for the calculation, [34] and δ > 0 corresponds to the compressive strain. More details about δ are provided in Figure S2, Supporting Information.…”

“…As demonstrated earlier in the magnetotransport results, the strained PIO film can have AIAO ordering. Then, in the pyrochlore lattice, a higher-rank magnetic multipole, called the A 2 -octupole (ω xyz ) [34,54] can be formed by the clusters xy , measured at 2, 4, and 15 K with external magnetic field ± 9 T, respectively. Equations ( 2) and ( 4) are used for the fitting.…”