Inverted anisotropy of the partially screened magnetic impurity

TL;DR

This paper reveals that in systems with strong spin-orbit coupling and anisotropy, the magnetic anisotropy can invert at finite temperatures before the impurity is fully screened, affecting magnetic behavior.

Contribution

It demonstrates the inversion of magnetic anisotropy in a single impurity due to strong coupling, using numerical and analytical methods, with implications for heavy-fermion materials.

Findings

Finite temperature window with anisotropy flip identified

Numerical renormalization group confirms anisotropy inversion

Coexistence of Curie response and Kondo fluctuations along hard axis

Abstract

We investigate a single magnetic impurity in the presence of strong spin-orbit coupling and single-ion anisotropy. We show that at sufficiently strong coupling there exists a finite temperature window, before the moment is completely screened, where the magnetic anisotropy of the system flips: the hard-axis becomes the easy-axis or vice versa. We derive this rigorously for a single impurity using numerical renormalization group calculations as well as Nozieres' strong-coupling limit and discuss its relevance to heavy-fermion compounds which order magnetically along the hard-direction. We show that the coexistence of Curie-like response and Kondo fluctuations is stabilized along the initially hard direction leading to the anisotropy switch.