We have synthesized a novel material, Sr3OsO6. The Tc value of this material is above 1000 K, which surpasses the Tc record among insulators for the first time in 88 years by more than 100 K. Density functional theory calculations revealed that the Jeff = 3/2 ferromagnetic insulating state of Sr3OsO6 originates from the large spin-orbit coupling of the 5d element Os.

Y. K. Wakabayashi*, et al.
Nature communications 10, 535 (2019).