Laser-driven first-order spin reorientation and Verwey phase transitions in magnetite Fe3O4 beyond the range of thermodynamic equilibrium

Ultrafast photo-induced phase transitions occurring under the impact of femtosecond laser pulses provide versatile opportunities for switching solids between distinctly-different crystalline, electronic, and magnetic states and thus modify their functional properties in a significant way. In this paper, we report on the laser-induced spin reorientation and Verwey phase transitions in a single crystalline ferrimagnetic magnetite Fe3O4. Using femtosecond optical and magneto-optical pump-probe techniques, we define the range of the initial sample temperatures and laser fluences when partial or complete photo-induced phase transitions occur from a monoclinic insulating to a cubic metallic state with concomitant switching of magnetic anisotropy from the uniaxial to the cubic one. We thus reveal a connection between these phase transitions when driven by femtosecond laser pulses. Using transient linear and quadratic magneto-optical effects, we examine magnetization dynamics launched the switching of the magnetic anisotropy axis. We unveil the presence of the domains undergoing the laser-induced phase transitions even below the established threshold fluence for the transitions, as well as when the material is initially in the cubic phase. This is the manifestation of the first order of these both laser-induced phase transitions beyond the range of thermodynamic equilibrium.

Automated summary

We report on the laser-induced spin reorientation and Verwey phase transitions in a single crystalline ferrimagnetic magnetite Fe3O4 using femtosecond optical and magneto-optical pump-probe techniques. By defining the range of initial sample temperatures and laser fluences, we observe partial or complete photo-induced phase transitions from a monoclinic insulating to a cubic metallic state, along with the switching of magnetic anisotropy. We also uncover the presence of laser-induced phase transition domains below the established threshold fluence and even when the material is initially in the cubic phase, demonstrating the first-order nature of these transitions beyond thermodynamic equilibrium.