Observation of Thermally Induced Piezomagnetic Switching in Cu2OSeO3 Polymorph Synthesized under High-Pressure

A polymorph of Cu₂OSeO₃ with the distorted kagome lattice is successfully obtained using the high-pressure synthesis technique (Cu₂OSeO₃-HP). The structural analysis using X-ray and neutron powder diffraction suggests that the tetrahedral Cu²⁺ clusters [similar to those in Cu₂OSeO₃ ambient-pressure phase (Cu₂OSeO₃-AP)] exist in Cu₂OSeO₃-HP but with three symmetry inequivalent sites. No structural change is observed between 1.5 K and the room temperature. The complex magnetic H-T phase diagram is established based on the temperature- and field-dependent magnetization data, indicating two distinct antiferromagnetic phases at low and intermediate temperatures, in addition to the higher-temperature spin-glass-like phase. The low temperature phase is identified by neutron powder diffraction refinements as a canted noncollinear antiferromagnetic order with a weak ferromagnetic component along the b-axis. Size of the refined ordered moment is ≈1.00(4) µ_B in Cu₂OSeO₃-HP, indicating a large enhancement compared to that of Cu₂OSeO₃-AP (≈0.61 µ_B). By applying a uniaxial stress, finite enhancement of weak ferromagnetic component in the noncollinear antiferromagnetic phase in Cu₂OSeO₃-HP is observed, which is the clear evidence of the piezomagnetic effect. Interestingly, the sign of the induced magnetization changes on heating from the low-temperature to the intermediate-temperature phases, indicating a novel piezomagnetic switching effect in this compound.