Seminar : Ultrafast Magnetization Manipulation in Multisublattice Magnets

On December 4,  we have the pleasure to welcome Marwan Deb from Université de Lorraine, France.

At 11H, he will give a seminar on “Ultrafast Magnetization Manipulation in Multisublattice Magnets” in room 434A.

Femtomagnetism is a relatively new and rapidly growing area of research that focuses on the ultrafast magnetization dynamics driven by fs laser pulses. It promises several potential applications in the fields of magnetic storage and spintronic technologies. In this talk, I will present my recent works on the ultrafast magnetization manipulation in metallic and insulating rare-earth transition-metal ferrimagnetic materials using ultrashort laser and hot-electron pulses.
The first part of the presentation is dedicated to the study of the magnetization dynamics in a specially engineered Gdx[FeCo]1-x based metallic structure with perpendicular magnetic anisotropy. Deterministic switching of the magnetization without any external magnetic field is demonstrated using either light or hot-electron single fs pulses. In both cases the switching is obtained for a broad range of composition, i.e. for a magnetic compensation temperature below or above room temperature. By performing time resolved measurements, we demonstrated that the magnetization reversal process induced by light and hot-electron excitation are similar, and that the full magnetization reversal takes place within 40 ps in either Gd-rich or FeCo-rich alloys. We suggest that the similar magnetization dynamics obtained by both types of excitation is related to the ballistic nature of hot-electron transport, which was clearly demonstrated in our structure.
In the second part, I will discuss the optical control of the magnetization dynamics in a 7 µm thick insulator film of Bi doped gadolinium iron garnet with uniaxial magnetic anisotropy perpendicular to the plane of the film. In addition to the ferromagnetic resonance mode, fs laser pulse allows exciting the Gd↔Fe exchange resonance mode over a broad range of temperature (50 to 300K) and magnetic fields (0 to 10T). We demonstrate that the frequency fexch associated to this exchange mode varies from the THz range at low temperature to GHz one when it approaches the compensation temperature TM. It also exhibits a linear decrease with the external magnetic field Hext in the vicinity of TM. These overall behaviors are shown to be consistent with the ferromagnetic resonance theory.

Keywords: Ultrafast magnetization dynamics and switching, ferrimagnetics, magneto-optical effects, ultrafast spectroscopy, electronic transport effects.

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