Fig. 4: Modelled thermal conductivity profiles of lower mantle minerals along a representative mantle geotherm.

a The red solid line represents the Λ_Fp75 with a conventional T ^–0.5 dependence for high-spin state and a weaker T ^–0.23 dependence as we experimentally found for low-spin state, while, for comparison, the red dashed line indicates the Λ_Fp75 with the conventional T ^–0.5 dependence for both high- and low-spin states. The black solid line shows the Λ_Fp25 with the conventional T ^–0.5 dependence for high-spin state and a weaker T ^–0.39 dependence for low-spin state; the black dashed line is the Λ_Fp25 with the conventional T ^–0.5 dependence for both high- and low-spin states. Overall, both Λ_Fp25 and Λ_Fp75 increase with depth, except for the range where the spin transition occurs. The low-spin Λ_Fp75 remains nearly a constant of ~3.6–3.8 W m⁻¹ K⁻¹ due to its weak temperature dependence. The small artifact discontinuities at the start and end of the spin transition result from the assumed temperature dependence in the mixed-spin state. Profiles of Ʌ_FeAl-Bm (FeAl-Bm, green dashed line) and Ʌ_davemaoite (Dvm, blue dashed line) are plotted for comparison. b From the top to the bottom of the lower mantle, the Ʌ_LM (blue solid line) increases two fold and converges to the previously modelled one (green dash-dotted line)¹⁴ at 8 W m⁻¹ K⁻¹ at the lowermost mantle. The sudden decrease in Ʌ profile above the CMB is due to the steep temperature rise.