High Field Anomalies of Equilibrium and Ultrafast Magnetism in Rare-Earth-Transition Metal Ferrimagnets

TL;DR

This study investigates the intrinsic magnetic anomalies in rare-earth ferrimagnets under high magnetic fields, revealing that triple hysteresis loops and ultrafast magnetic behaviors are inherent properties linked to orbital momentum, not sample inhomogeneities.

Contribution

It demonstrates that the observed magnetic anomalies are intrinsic to rare-earth ferrimagnets and provides a theoretical model incorporating orbital momentum to explain equilibrium and ultrafast magnetic phenomena.

Findings

Triple hysteresis loops near compensation temperature are intrinsic.

Theoretical model reproduces equilibrium magnetic behavior.

Orbital momentum influences ultrafast spin dynamics.

Abstract

Magneto-optical spectroscopy in fields up to 30 Tesla reveals anomalies in the equilibrium and ultrafast magnetic properties of the ferrimagnetic rare-earth-transition metal alloy TbFeCo. In particular, in the vicinity of the magnetization compensation temperature, each of the magnetizations of the antiferromagnetically coupled Tb and FeCo sublattices show triple hysteresis loops. Contrary to state-of-the-art theory, which explains such loops by sample inhomogeneities, here we show that they are an intrinsic property of the rare-earth ferrimagnets. Assuming that the rare-earth ions are paramagnetic and have a non-zero orbital momentum in the ground state and, therefore, a large magnetic anisotropy, we are able to reproduce the experimentally observed behavior in equilibrium. The same theory is also able to describe the experimentally observed critical slowdown of the spin dynamics in the vicinity of the magnetization compensation temperature, emphasizing the role played by the orbital momentum in static and ultrafast magnetism of ferrimagnets.