Unconventional spin dynamics in the non-collinear phase of a ferrimagnet

TL;DR

This study explores how the magnetic phase (non-collinear vs. collinear) in ferrimagnets influences ultrafast spin dynamics, revealing new effects and potential for data storage and processing.

Contribution

It is the first to analyze laser-induced spin dynamics in the non-collinear phase of ferrimagnets, highlighting phase-dependent effects on spin modes.

Findings

Non-collinearity affects the sensitivity of the quasi-antiferromagnetic mode to magnetic fields.

The quasiferromagnetic mode peaks near the magnetization compensation point.

At the phase transition, the quasiferromagnetic mode softens and its amplitude increases significantly.

Abstract

Ferrimagnets containing several partially compensated magnetic sublattices are considered the most promising materials for all-optical data storage and for ultrafast communications based on spin waves. There are two magnetic phases of the ferrimagnets: collinear and non-collinear ones. Up to now spin dynamics in ferrimagnets has been studied mostly in the collinear state without paying much attention to the kind of the magnetic phase. Here we investigate laser induced ultrafast spin dynamics in a rare-earth iron garnet film in the noncollinear phase as well. We identify a crucial influence of the magnetic phase on the excited spin modes which allowed us to discover several prominent effects previously overlooked. In particular, the non-collinearity makes the quasi-antiferromagnetic mode sensitive to the external magnetic field and brings its frequency close to the frequency of the quasiferromagnetic mode. The latter maximizes near the magnetization compensation point and vanishes towards the collinear phase. Spectacularly, at the phase transition the quasiferromagnetic mode becomes soft and its amplitude significantly increases reaching 7{\deg}. This opens new opportunities for the ultrafast control of spins in ferrimagnets for nonthermal data storage and data processing.