Fig. 3: Lattice expansion of FeRh in FeRh/Cu heterostructure.
From: Spin current driven by ultrafast magnetization of FeRh
a, b The reflectivity change (ΔR) during the phase transition of FeRh. The color indicates the pump fluence in a unit of J m−2: 0.9 (black square), 2.2 (red circles), 3.5 (blue up-triangles), 5.3 (green down-triangles), and 7.1 (magenta diamonds). a The raw ΔR consists of the temperature-induced (ΔRT). acoustic-wave-induced (ΔRA), and lattice-expansion-induced (ΔRL) ones: temperature rise produces a fast rising in ΔRT at around time zero; acoustic wave produces a peak of ΔRA at 5 ps, which corresponds to a round trip of acoustic wave through the FeRh thickness; a non-linear dependence on the pump fluence comes from ΔRL, which is caused by the phase transition. b The magnetic-field-dependent part of ΔR, difference of ΔR with and without an external magnetic field of 0.15 T, comes from a partial change of ΔRL by the magnetic field without a contribution from ΔRT and ΔRA. It shows a significant rising at 2.5 ps, which has a nontrivial dependence on the pump fluence: a threshold at pump fluence of >2 J m−2 and a saturation at a pump fluence of >5 J m−2.
