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Copper oxide selenite is an inorganic compound with the chemical formula Cu₂OSeO₃. It is an electrically insulating, piezoelectric and piezomagnetic material, which becomes a ferrimagnet upon cooling below 58 K. As of 2021, Cu₂OSeO₃ is the only insulating material that hosts magnetic skyrmions.

Synthesis

Cu₂OSeO₃ polycrystals can be grown by heating a 2:1 molar mixture of CuO and SeO₂ powders at 600 °C for 12 hours in vacuum. They can be converted into olive-green single crystals ca. 4 mm in size by chemical vapor transport. NH₄Cl is used as the transport agent; it sublimes at 340 °C, yielding NH₃ and HCl gases.

Structure

Cu₂OSeO₃ crystals have a cubic, distorted pyrochlore structure built by Cu₄O and SeO₃ units. The spins on three Cu ions in each tetrahedron (Cu1 sites) are aligned, while the Cu2 spin is facing in the opposite direction, resulting in a ferrimagnetic order. The helical spin and skyrmion textures emerge at low magnetic fields due to the Dzyaloshinskii-Moriya interaction.

• (a) Crystal structure of Cu₂OSeO₃ consisting of (b) Cu1 bipyramids and (c) Cu2 distorted square-based pyramids. Bonds to Se ions are omitted for clarity. (d) The ferrimagnetic structure of Cu₂OSeO₃ with spins (green arrows) on Cu1 site antiparallel to the spins (red arrows) on Cu2 sites.

Properties

Cu₂OSeO₃ is a ferrimagnet, and all its properties below the Curie temperature strongly depend on magnetic field. With increasing field, its spin texture changes from helical stripes to conical stripes or skyrmion lattice, and then to a "field polarized", i.e., ferrimagnetic alignment. Thermal conductivity peaks around 9 K with a value of ca. 400 W/(m·K). The magnetization damping constant is 1×10 at 5 K. This value is only 4 times larger than that of yttrium iron garnet, which has the lowest magnetization damping value among all materials. This property is advantageous for high-frequency electronic applications, as it results in low current-induced heat.

References

1. ^ Panella, Jessica R.; Trump, Benjamin A.; Marcus, Guy G.; McQueen, Tyrel M. (2017). "Seeded Chemical Vapor Transport Growth of Cu₂OSeO₃". Crystal Growth & Design. 17 (9): 4944–4948. arXiv:1706.02411. doi:10.1021/acs.cgd.7b00879. S2CID 103302936.
2. ^ Bos, Jan-Willem G.; Colin, Claire V.; Palstra, Thomas T. M. (2008). "Magnetoelectric coupling in the cubic ferrimagnet Cu₂OSeO₃". Physical Review B. 78 (9): 094416. arXiv:0808.3955. Bibcode:2008PhRvB..78i4416B. doi:10.1103/PhysRevB.78.094416. S2CID 56431702.
3. Versteeg, R. B.; Vergara, I.; Schäfer, S. D.; Bischoff, D.; Aqeel, A.; Palstra, T. T. M.; Grüninger, M.; van Loosdrecht, P. H. M. (2016). "Optically probed symmetry breaking in the chiral magnet Cu₂OSeO₃". Physical Review B. 94 (9): 094409. arXiv:1605.01900. Bibcode:2016PhRvB..94i4409V. doi:10.1103/PhysRevB.94.094409. S2CID 118390265.
4. ^ Prasai, N.; Akopyan, A.; Trump, B. A.; Marcus, G. G.; Huang, S. X.; McQueen, T. M.; Cohn, J. L. (2019). "Spin phases of the helimagnetic insulator Cu₂OSeO₃ probed by magnon heat conduction". Physical Review B. 99 (2): 020403. arXiv:1901.01242. Bibcode:2019PhRvB..99b0403P. doi:10.1103/PhysRevB.99.020403. S2CID 119506811.
5. Stasinopoulos, I.; Weichselbaumer, S.; Bauer, A.; Waizner, J.; Berger, H.; Maendl, S.; Garst, M.; Pfleiderer, C.; Grundler, D. (2017). "Low spin wave damping in the insulating chiral magnet Cu₂OSeO₃". Applied Physics Letters. 111 (3): 032408. arXiv:1705.03416. Bibcode:2017ApPhL.111c2408S. doi:10.1063/1.4995240. S2CID 13560805.

• Selenites
• Copper(I) compounds