Ultrafast spin dynamics in ferrimagnets with compensation point

Area of Science:

• Condensed Matter Physics
• Ultrafast Magnetism
• Materials Science

Background:

• Ferrimagnetic materials, particularly rare-earth-transition metal alloys like GdFeCo, exhibit complex magnetization dynamics.
• Understanding these dynamics is crucial for developing advanced magnetic technologies.
• Previous studies have reported ultrafast demagnetization phenomena in these materials, especially near specific magnetic transitions.

Purpose of the Study:

• To derive an effective Lagrangian for modeling magnetization dynamics in ferrimagnets with a magnetization compensation point.
• To explain the observed ultrafast magnetization dynamics in GdFeCo amorphous alloys near the spin-flop transition.
• To provide a theoretical framework applicable to other ultrafast magnetism phenomena in similar materials.

Main Methods:

• Derivation of an effective Lagrangian.
• Modeling of magnetization dynamics under ultrafast demagnetization.
• Analysis of the noncollinear magnetic phase and sublattice torques.
• Investigation of temperature and magnetic field dependencies.

Main Results:

• The derived model successfully explains magnetization dynamics in the noncollinear phase of GdFeCo alloys.
• Ultrafast demagnetization by a femtosecond laser pulse induces a torque on sublattice magnetizations.
• Dynamics show strong dependence on temperature and magnetic field, with critical slowdown near the spin-flop transition.
• Amplitude of dynamics dramatically increases near the spin-flop phase transition.

Conclusions:

• The developed theoretical framework accurately describes ultrafast magnetization dynamics in ferrimagnets near their compensation point.
• The model provides insights into the role of laser-induced demagnetization and sublattice torques.
• This work is expected to stimulate further research into ultrafast magnetism in noncollinear spin systems.