Exploring structure and magnetism of collapsed lanthanides

By using DFT within VASP [1] and DFT+DMFT within CASTEP codes [2], we study the collapsed phases of Tb, Gd, Dy, Sm, Nd and Y at extreme pressure up to 240GPa.
In Tb, Gd, Dy we show that the collapsed phases have a 16-atom orthorhombic structure (oF16) not previously seen in the elements, whereas in Nd we show that it has an eight-atom orthorhombic structure (oF8) previously reported in several actinide elements. oF16 and oF8 are members of a new family of layered elemental structures, the discovery of which reveals that the high-pressure structural systematics of the lanthanides, actinides, and group-III elements (Sc and Y) are much more related than previously imagined. Our electronic structure calculations of Tb, combined with quantum many-body corrections, confirm previous and recent experimental observations by using synchrotron x-ray diffraction (see the Ref.[3] and the references therein), and predict that the collapsed orthorhombic phase is a ferromagnet, nearly degenerate with an antiferromagnetic state between 60 and 80 GPa. We also discuss in detail the magnetic properties of the lanthanides studied.

[1] G. Kresse and et al., Phys. Rev. B 59, 1758 (1999).
[2] M. I. McMahon, et al. Phys. Rev. B 100, 024107 (2019).
[3] E. Plekhanov et al. Phys. Rev. B 98, 075129 (2018).