Abstract
Controlling magnetic order on ultrashort timescales is crucial for engineering the next-generation magnetic devices that combine ultrafast data processing with ultrahigh-density data storage. An appealing scenario in this context is the use of femtosecond (fs) laser pulses as an ultrafast, external stimulus to fully set the orientation and the magnetization magnitude of a spin ensemble. Achieving such control on ultrashort timescales, e.g., comparable to the excitation event itself, remains however a challenge due to the lack of understanding the dynamical behavior of the key parameters governing magnetism: The elemental magnetic moments and the exchange interaction. Here, we investigate the fs laser-induced spin dynamics in a variety of multi-component alloys and reveal a dissimilar dynamics of the constituent magnetic moments on ultrashort timescales. Moreover, we show that such distinct dynamics is a general phenomenon that can be exploited to engineer new magnetic media with tailor-made, optimized dynamic properties. Using phenomenological considerations, atomistic modeling and time-resolved X-ray magnetic circular dichroism (XMCD), we demonstrate demagnetization of the constituent sub-lattices on significantly different timescales that depend on their magnetic moments and the sign of the exchange interaction. These results can be used as a “recipe” for manipulation and control of magnetization dynamics in a large class of magnetic materials.
Highlights
Femtosecond laser-induced controlling of ferromagnetic order[1] has intrigued researchers since the pioneering work of Beaurepaire et al.,[2] who found that fs optical excitation of ferromagnetic Ni can demagnetize the sample on a sub-picosecond time-scale
Atomistic modeling and time-resolved X-ray magnetic circular dichroism (XMCD), we demonstrate demagnetization of the constituent sub-lattices on signicantly di®erent timescales that depend on their magnetic moments and the sign of the exchange interaction
Using phenomenological modeling and atomistic spin simulations, we show that their demagnetization dynamics is distinct and elementspecic
Summary
Femtosecond (fs) laser-induced controlling of ferromagnetic order[1] has intrigued researchers since the pioneering work of Beaurepaire et al.,[2] who found that fs optical excitation of ferromagnetic Ni can demagnetize the sample on a sub-picosecond time-scale. To understand qualitatively how the demagnetization time changes by going from the pure element to the alloy, we considerrst the limiting case of small x In this limit, we simplify the theory using eðxÞ The exchange relaxation in the Invar regime can make the dynamics of Ni and Fe more distinct than anticipated solely from the di®erence of the magnetic moments, which is the trend observed in the atomistic and experimental results shown below
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