Abstrakt
The integration of spintronic devices in electronics may provide a potential solution to satisfy the endless demand for high-bit-density and fast data-processing-speed storage media. So far, magnetization or spin manipulation in spintronic devices has generally been achieved by applying external magnetic fields leading to switching speeds in the hundreds of picoseconds. Magnetization switching induced by femtosecond lasers shows vast potential for enhancing data processing speed. Particularly, all-optical helicity-dependent switching (AOHDS) can trigger magnetization switching on tens of femtosecond timescales. In the AOHDS process, the magnetization is induced with circularly polarized light via the optical angular momentum transfer.
We have studied the magnetic response of a demagnetized FePt granular media sample to polarized light with a final aim of AOHDS. The resulting magneto-optical (MO) images of lines written by polarized femtosecond laser pulses have shown a strong contribution to the signal, particularly for high laser powers. In previously published papers, demagnetization was observed in the area of the highest intensity - the middle of the recorded line/spot. However, in our case, the signal contribution same sign for both helicities and its shape indicates that the signal has a non-magnetic origin. The amplitude of the non-magnetic signal decays exponentially over several minutes as the reflection of the sample surface changes. Gradually, the original state is restored to some extent due to the cooling of the sample. The non-magnetic contribution is, to our best knowledge, not observed in previous works addressing AOHDS in FePt nanograin media. Understanding all-optical magnetic switching and its artifacts are critical for commercial applications in electronic/spintronic devices, which is the ultimate goal.