Model of ultrafast demagnetization driven by spin-orbit coupling in a photoexcited antiferromagnetic insulator Cr2O3

Tuning the photodynamics of sub-nanometer neutral chromium oxide clusters through sequential oxidation

Sub-nanometer neutral chromium oxide clusters were produced in the gas phase through laser ablation and their low-lying excited state lifetimes were measured using femtosecond pump-probe spectroscopy. Time-dependent density functional theory calculations relate the trends in experimental lifetimes to the cluster's electronic structure. The photoexcited (CrO₂)_n (n < 5) cluster transients with the absence of up to four O atoms (Cr_nO_2n-x, x < 5) exhibit a ∼30 fs and sub-ps lifetime, attributed to instantaneous metallic e-e scattering and vibrationally mediated charge carrier relaxation, respectively. A long-lived (>2 ps) response is found in both small and clusters with low O content, indicating that terminal CrO bonds facilitate efficient excited state relaxation. The ∼30 fs transient signal fraction grows nearly linearly with oxidation, matching the amount of O-2p to Cr-3d charge transfer character of the photoexcitation and suggesting a gradual transition between semiconducting and metallic behavior in chromium oxide clusters at the molecular level. The results presented herein suggest that the photocatalytic properties of chromium oxides can be tunable based on size and oxidation.

Increased Excited State Metallicity in Neutral Cr2On Clusters (n < 5) upon Sequential Oxidation

Excited state lifetimes of neutral Cr₂O_n (n < 5) clusters were measured using femtosecond pump-probe spectroscopy. Density functional theory calculations reveal that the excited state dynamics are correlated with changes in the cluster's electronic structure with increasing oxidation. Upon absorption of a UV (400 nm) photon, the clusters exhibit features attributed to three separate relaxation processes. All clusters exhibit similar subpicosecond lifetimes, attributed to vibrational relaxation. However, the ∼30 fs transient signal fraction grows linearly with oxidation, matching the amount of O to Cr charge transfer character of the photoexcitation and highlighting a gradual transition between semiconducting and metallic behavior at the molecular level. A long-lived (>2.5 ps) response is recorded only in clusters with significant d-electron character, suggesting that adiabatic relaxation back to the ground state is efficient in heavily oxidized clusters, due to the presence of terminal O atoms. The simple picture of sequential oxidation of Cr₂O_n reveals a linear variation in the contributions of each relaxation component to the total transient signals, therefore opening possibilities for the design of new molecular spintronic materials.

Ultrafast photoinduced dynamics in Prussian blue analogues

A review on ultrafast photoinduced processes in molecule-based magnets with an emphasis on Prussian blue analogues.