Photoinduced Demagnetization and Insulator-to-Metal Transition in Ferromagnetic Insulating ${\mathrm{BaFeO}}_3$ Thin Films

We studied the electronic and magnetic dynamics of ferromagnetic insulating ${\mathrm{BaFeO}}_3$ thin films by using pump-probe time-resolved resonant x-ray reflectivity at the Fe $2p$ edge. By changing the excitation density, we found two distinctly different types of demagnetization with a clear threshold behavior. We assigned the demagnetization change from slow ($\sim 150\mathrm{ps}$) to fast ($<70\mathrm{ps}$) to a transition into a metallic state induced by laser excitation. These results provide a novel approach for locally tuning magnetic dynamics. In analogy to heat-assisted magnetic recording, metallization can locally tune the susceptibility for magnetic manipulation, allowing one to spatially encode magnetic information.

Figure 1

(a) Geometry of the measurements. (b) shows the reflectivity (top) and MCDR (bottom) intensity from ${\mathrm{BaFeO}}_3$ thin films as a function of $2\theta$. (c) shows the photon energy dependence of reflectivity (top) and MCDR (bottom).

Figure 2

Time evolution of (a) XMCD intensity and (b) reflectivity of ${\mathrm{BaFeO}}_3$ thin films for various pump laser fluence. All the curves, except for the case of $10\mathrm{mJ}/{\mathrm{cm}}^2$, are shifted upward for clarity. (c) The reflectivity spectra with and without the pump effect (top). The difference of the spectra (bottom).

Figure 3

The demagnetization time ${\tau }_{\text{decay}}$ (top), determined from Fig. 2, and the magnitude of decay of reflectivity due to the pump (bottom) are shown.

Figure 4

Mechanism of the insulator-to-metal transition induced by the strong laser excitation.