Magnetoelasticity-driven phase inversion of ultrafast spin precession in NixFe100-x thin films

TL;DR

This study demonstrates that magnetoelastic effects critically influence ultrafast spin precession phase inversion in NixFe100-x thin films, revealing a new mechanism beyond traditional temperature-dependent magnetic field considerations.

Contribution

It provides the first comprehensive evidence that magnetoelasticity governs phase inversion in ultrafast spin dynamics without structural changes, highlighting its importance in spintronic materials.

Findings

Sudden Pi-phase inversion occurs in NixFe100-x films without structural change.

Magnetoelastic fields compete with conventional magnetic fields near x=95.3.

Temperature and composition-dependent parameters determine spin dynamics.

Abstract

We present strong evidences for the deterministic role of magnetoelasticity in ultrafast spin dynamics of ferromagnetic NixFe100-x alloy films. Without a change in the crystal structure, we observed sudden Pi-phase inversion of the spin precession in the range of x = 87.0 - 97.5. In addition, it was found that the phase was continuously changed and reversed its sign by varying the pump fluence. These cannot be explained simply by temperature dependence of magnetocrystalline, demagnetizing, and Zeeman fields which have been conventionally considered so far in describing the spin dynamics. Through the temperature- and composition-dependent simulations adding the magnetoelastic field generated from the lattice thermal strain, we revealed that the conventional and magnetoelastic fields were competing around x = 95.3, where the spin dynamics showed the largest phase shift. For analytic understanding, we further show that the temperature-dependent interplay of the Curie temperature, saturation magnetization, and magnetostriction, which are demonstrated to be the most important macroscopic parameters, determines the ultrafast spin dynamics. Our extensive study emphasizes that magnetoelasticity is the key ingredient for fully understanding the driving mechanism of ultrafast spin dynamics.