Dresden 2006 – scientific programme

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MA: Magnetismus

MA 33: Spin-Dynamics, Magnetization Reversal III

MA 33.7: Talk

Thursday, March 30, 2006, 16:45–17:00, HSZ 403

Ultrafast Demagnetization of Ferromagnetic Films Probed by XMCD — •Christian Stamm, Cosmin Lupulescu, Hermann Dürr, and Wolfgang Eberhardt — BESSY, Albert-Einstein-Str. 15, 12489 Berlin, Germany

We investigate the dynamic response of magnetic thin films subjected to high-intensity fs laser pulses. Using the X-ray magnetic circular dichroism (XMCD) we observe the evolution of the magnetization as a function of time delay between laser pump and X-ray probe pulse. This technique complementary to the magneto-optic Kerr effect, allows us to separately determine spin and orbital moments by a sum rule calculation. Our goal is to get new insight into the process of fs demagnetization, especially concerning the conservation of the total angular momentum.

The experiments were performed at the BESSY Synchrotron source using gated detection of single X-ray bunches following a pump pulse from a synchronized fs laser. During normal operation, the X-ray pulse length is ~50 ps. To further improve the time resolution we also used the No-dqlow-alphaNo-dq mode of the Synchrotron reducing the pulse length down to 5 ps.

We find that a Ni thin film with in-plane magnetization and a CoPd multilayer with perpendicular anisotropy both can be demagnetized in less than 10 ps. Additionally, X-ray dichroism spectra are recorded at different time delays, allowing the determination of spin and orbital moments of the excited film. The use of fs X-ray pulses from the slicing source currently under commissioning at BESSY will further increase the time resolution of our experiments to the fs regime.