Monday, February 20, 2012

1202.3874 (Andreas Mann et al.)

Insights into ultrafast demagnetization in pseudo-gap half metals    [PDF]

Andreas Mann, Jakob Walowski, Markus Münzenberg, Stefan Maat, Matthew J. Carey, Jeffrey R. Childress, Claudia Mewes, Daniel Ebke, Volker Drewello, Günter Reiss, Andy Thomas
Interest in femtosecond demagnetization experiments was sparked by Bigot's
discovery in 1995. These experiments unveil the elementary mechanisms coupling
the electrons' temperature to their spin order. Even though first quantitative
models describing ultrafast demagnetization have just been published within the
past year, new calculations also suggest alternative mechanisms.
Simultaneously, the application of fast demagnetization experiments has been
demonstrated to provide key insight into technologically important systems such
as high spin polarization metals, and consequently there is broad interest in
further understanding the physics of these phenomena. To gain new and relevant
insights, we perform ultrafast optical pump-probe experiments to characterize
the demagnetization processes of highly spin-polarized magnetic thin films on a
femtosecond time scale. Previous studies have suggested shifting the Fermi
energy into the center of the gap by tuning the number of electrons and thereby
to study its influence on spin-flip processes. Here we show that choosing
isoelectronic Heusler compounds (Co2MnSi, Co2MnGe and Co2FeAl) allows us to
vary the degree of spin polarization between 60% and 86%. We explain this
behavior by considering the robustness of the gap against structural disorder.
Moreover, we observe that Co-Fe-based pseudo gap materials, such as partially
ordered Co-Fe-Ge alloys and also the well-known Co-Fe-B alloys, can reach
similar values of the spin polarization. By using the unique features of these
metals we vary the number of possible spin-flip channels, which allows us to
pinpoint and control the half metals electronic structure and its influence
onto the elementary mechanisms of ultrafast demagnetization.
View original: http://arxiv.org/abs/1202.3874

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