Subpicosecond Magnetization Reversal across Ferrimagnetic Compensation Points

Subpicosecond magnetization reversal is experimentally demonstrated by ultrafast heating of a ferrimagnet across its compensation points, under an applied magnetic field. While the reversal is initiated by crossing the magnetization compensation temperature, the short reversal time is related to the angular momentum compensation, where the dynamics of the system is highly accelerated owing to the divergence of the gyromagnetic ratio. These results demonstrate the feasibility of subpicosecond magnetization reversal previously believed impossible.

Figure 1

Transient Faraday effect traces at different pump fluences. The variation of the magneto-optical signal was plotted relative to the total Faraday rotation at room temperature. The data are offset for clarity. Insets: hysteresis loops measured at negative delay for distinct pump fluences.

Figure 2

(a) Temperature dependence of the coercive field $H_{\mathbf{c}}$ in the GdFeCo sample. The divergence of $H_{\mathbf{c}}$ indicates the presence of $T_{\mathbf{M}}$. The inset of the figure shows schematically the ferrimagnetic system in an applied magnetic field below and above $T_{\mathbf{M}}$. Depending on the strengths of the applied magnetic field, two different dynamic regimes can be distinguished: ($\mathbf{A}$) for ${\mathbf{H}}_{\mathrm{ext}}>H_c^{\mathrm{room}}$ and ($\mathbf{B}$) for ${\mathbf{H}}_{\mathrm{ext}}<H_c^{\mathrm{room}}$. (b) Qualitative description of the magnetization dynamics induced by the first pump pulses, at a $6.29\mathrm{mJ}/{\mathrm{cm}}^2$ fluence, for the two different conditions [($\mathbf{A}$) and ($\mathbf{B}$)]. The arrows indicate the time when the pump pulses hit the sample (1 ms between two pulses). The inset shows the hysteresis loop measured at negative delay for the $6.29\mathrm{mJ}/{\mathrm{cm}}^2$ pump fluence.

Figure 3

Transient magnetization reversal dynamics measured for a pump fluence of $6.29\mathrm{mJ}/{\mathrm{cm}}^2$. Insets show hysteresis loops measured at distinct pump-probe delays. The loops demonstrate the magnetization reversal after about 700 fs.

Figure 4

Faraday rotation ${\theta }_{\mathbf{F}\mathbf{e}\mathbf{C}\mathbf{o}}$ at $\lambda =805\mathrm{nm}$ as a function of temperature representing the temperature dependence of the FeCo sublattice magnetization. Here, ${\mathbf{M}}_{\mathbf{F}\mathbf{e}\mathbf{C}\mathbf{o}}$ represents the FeCo sublattice magnetization at the room temperature.