Theory of magnetic ordering in the heavy rare earths: ab-initio electronic origin of pair- and four- spin interactions

TL;DR

This paper develops an ab-initio theory to explain the magnetic phase diagram of heavy rare earth elements, linking electronic structure changes to magnetic ordering and phase transitions.

Contribution

It introduces a comprehensive ab-initio disordered local moment theory that connects electronic structure to magnetic phases in heavy rare earths, including phase transition mechanisms.

Findings

Generic magnetic phase diagram for heavy rare earths.

Loss of Fermi surface nesting drives HAFM-FM transition.

Electronic structure influences magnetic phase stability.

Abstract

We describe an ab-initio disordered local moment theory for long period magnetic phases and investigate the temperature and magnetic field dependence of the magnetic states in the heavy rare earth elements (HRE), namely paramagnetic, conical and helical anti-ferromagnetic(HAFM), fan and ferromagnetic (FM) states. We obtain a generic HRE magnetic phase diagram which is consequent on the response of the common HRE valence electronic structure to f-electron magnetic moment ordering. The theory directly links the first order HAFM-FM transition to the loss of Fermi surface nesting as well as providing a template for analysing the other phases and exposing where f-electron correlation effects are particularly intricate. Gadolinium, for a range of hexagonal, close-packed lattice constants, c and a, is the prototype and applications to other HREs are made straightforwardly by scaling the pair and quartic local moment interactions with de Gennes factors and choosing appropriate lanthanide contracted c and $a$ values.