Revealing the Nature of the Ultrafast Magnetic Phase Transition in Ni by Correlating Extreme Ultraviolet Magneto-Optic and Photoemission Spectroscopies

TLDR

The study employs time‑ and angle‑resolved photoemission together with time‑resolved transverse magneto‑optical Kerr effect at extreme ultraviolet wavelengths to uncover the universal ultrafast photoinduced magnetic phase transition in Ni. The ultrafast magnetic response of Ni depends on laser fluence, showing a modest magnetization drop at low fluence and complete quenching at high fluence; demagnetization and recovery timescales are identical across probes, with spin energy absorbed within 20 fs, spectroscopic signatures appearing after ~200 fs, and recovery spanning 500 fs to >70 ps, revealing two competing channels and coexisting phases.

Abstract

By correlating time- and angle-resolved photoemission and time-resolved transverse magneto-optical Kerr effect measurements, both at extreme ultraviolet wavelengths, we uncover the universal nature of the ultrafast photoinduced magnetic phase transition in Ni. This allows us to explain the ultrafast magnetic response of Ni at all laser fluences-from a small reduction of the magnetization at low laser fluences, to complete quenching at high laser fluences. Both probe methods exhibit the same demagnetization and recovery timescales. The spin system absorbs the energy required to proceed through a magnetic phase transition within 20 fs after the peak of the pump pulse. However, the spectroscopic signatures of demagnetization of the material appear only after ≈200 fs and the subsequent recovery of magnetization on timescales ranging from 500 fs to >70 ps. We also provide evidence of two competing channels with two distinct timescales in the recovery process that suggest the presence of coexisting phases in the material.