OR2 : Dynamics of magnetization and multiferroïc materials

Inertial dynamics of the magnetization

Hard disk writing and data storage in MRAM memories are controlled by the process of magnetization reversal by applying a magnetic field to magnetic bits. The dynamics of the magnetization during this reversal is described by the Landau-Lifshitz-Gilbert (LLG) phenomenological equation which correctly reproduces the reversal of the magnetic bit on the time scale of the nanosecond. The possibility of magnetization dynamics at much faster time scales has recently been taken into account by incorporating an inertial term in the LLG equation which generates much faster dynamics and notably induces nutation motion magnetization which is added to the usual dynamics of precession.
Our recent theoretical studies and numerical simulations of the inertial regime of the magnetization could offer a major interest in the ultrafast spin dynamics for spintronic device applications.


FMR peaks obtained by numerical simulations for a single spin dynamics.
The nutation peak at high frequency is the signature of inertia. In the case of interacting spins, a new collective mode appears, called the nutation wave which has distinct properties compared to the usual spin wave.

Interacting spins

Dispersion relation of the nutation wave (upper curve, Higgs mode with a gap at k=0) and spin wave (lower curve, gapless Goldstone mode).

Nutation wave

Multiferroïc materials

Multiferroic materials
Polarized Raman scattering on orthorhombic RCrO3 (R = La, Pr, Nd, and Sm) single crystals was measured at room temperature. Phonon frequency evolutions as a function of orthorhombic distortion were investigated and highlighted a complex behavior for several modes. phonon modes were unambiguously assigned on the basis of both Raman selection rules and lattice dynamics calculations within density functional perturbations theory.

Polarized raman