Coherent THz optical lattice and hybridized phonon–magnon modes are triggered by femtosecond laser pulses in the antiferromagnetic van der Waals semiconductor FePS₃. The laser‐driven lattice and spin dynamics are investigated in a bulk crystal as well as in a 380 nm‐thick exfoliated flake as a function of the excitation photon energy, sample temperature and applied magnetic field. The pump‐probe magneto‐optical measurements reveal that the amplitude of a coherent phonon mode oscillating at 3.2 THz decreases as the sample is heated up to the Néel temperature. This signal eventually vanishes as the phase transition to the paramagnetic phase occurs, thus revealing its connection to the long‐range magnetic order. In the presence of an external magnetic field, the optically triggered 3.2 THz phonon hybridizes with a magnon mode, which is utilized to excite the hybridized phonon–magnon mode optically. These findings open a pathway toward the optical control of coherent THz photo–magnonic dynamics in a van der Waals antiferromagnet, which can be scaled down to the 2D limit.

All-optical switching (AOS) of magnetization in ferri- and ferromagnetic thin films has in recent years attracted a strong interest since it allows magnetization reversal in the absence of applied magnetic field. Here we investigate AOS in ${[\mathrm{Co}/\mathrm{Pt}]}_N$ multilayers. The coercivity ($H_C$) of the multilayers was tuned either by varying the bilayer repetition number ($N$) or the sample temperature ($T$). During the AOS experiments, we first illuminated the multilayers by a sequence of femtosecond laser pulses with varying fluence, light polarization, and repetition rate. The optically affected area was then imaged with magneto-optical Kerr microscopy. Our results indicate that the optical pulses can trigger either AOS or initiate an all-optical domain formation (AODF). The laser fluence required for AOS scales linearly with $H_C$ and depends on a precise tuning of laser pulse fluence, repetition rate, and light polarization. Furthermore, the magnetic response of the samples at a varying ambient temperature (down to 50 K) and for different time intervals between subsequent laser pulses point to the crucial role of domain wall dynamics in optical control of magnetization in ferromagnetic multilayers.

We experimentally investigated magnetization relaxation dynamics in the largely unexplored time window extending from few picoseconds up to two nanoseconds following femtosecond laser pulse excitation. We triggered magnetization dynamics in ${\left[\mathrm{Co}\left(0.4\mathrm{nm}\right)/\mathrm{Pt}\left(0.7\mathrm{nm}\right)\right]}_3$ multilayers and measured the resulting magneto-optic response by recording both transient hysteresis loops as well as transients of magnetization dynamics. We observe that the coercive field of the sample is still strongly suppressed even ∼1 ms after the laser excitation, which is three orders of magnitude longer than the recovery time of the magnetization amplitude. In addition, we succeeded to fit the magnetization relaxation data in the entire experimentally observed time window by considering two phenomenological time constants ${\tau }_f^{*}$ and ${\tau }_s^{*}$ describing fast (ps) and slow (ns) magnetization relaxation processes, respectively. The fits of the data suggest a magnetic field dependent relaxation slowdown beyond 100 ps after excitation. We observe an explosion of the ${\tau }_f^{*}$ and ${\tau }_s^{*}$ values when the magnetization is completely quenched and relaxes intrinsically in the absence of an external magnetic field. We interpret the phenomenological time constants ${\tau }_f^{*}$ and ${\tau }_s^{*}$ using an intuitive physical picture based on the Landau-Lifshitz-Bloch model and numerical solutions of the extended three-temperature model [Shim et al., Sci. Rep. 10, 6355 (2020)].

The magnetic proximity effect provides a promising way to increase the low Curie temperature (T_C) of europium monoxide (EuO) toward or even above room temperature, while keeping its stoichiometry and insulating properties. This work studies EuO/Co bilayers using static and time‐resolved magneto‐optical Kerr effect measurements, and explores the influence of magnetic proximity on T_C and on the spin dynamics in EuO. Excitation above the EuO bandgap results in an ultrafast enhancement of the EuO magnetization followed by a demagnetization within nanoseconds. This behaviour is also visible upon selectively photoexciting Co in the EuO/Co bilayer placed in an out‐of‐plane magnetic field, which is attributed to propagation of a superdiffusive spin current from Co into EuO. As the spin dynamics of Co shows a transient thermal demagnetization, the bilayer provides a system where the transient magneto‐optical signal can be tuned in amplitude and sign by varying external parameters such as the sample temperature or pump fluence. Moreover, in a strong excitation regime it is possible to measure the magnetic hysteresis of the underlying EuO, which is present up to room temperature – giving experimental evidence for the presence of a tuneable magnetic proximity coupling between Co and EuO.