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

A polymorph of Cu 2 OSeO 3 with the distorted kagome lattice is successfully obtained using the high‐pressure synthesis technique (Cu 2 OSeO 3 ‐HP). The structural analysis using X‐ray and neutron powder diffraction suggests that the tetrahedral Cu 2+ clusters [similar to those in Cu 2 OSeO 3 ambient‐pressure phase (Cu 2 OSeO 3 ‐AP)] exist in Cu 2 OSeO 3 ‐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 Cu 2 OSeO 3 ‐HP, indicating a large enhancement compared to that of Cu 2 OSeO 3 ‐AP (≈0.61 µ B ). By applying a uniaxial stress, finite enhancement of weak ferromagnetic component in the noncollinear antiferromagnetic phase in Cu 2 OSeO 3 ‐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.