Ultrafast and Distinct Spin Dynamics in Magnetic Alloys

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 signi¯-cantly di®erent 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.

Thermally induced magnetization switching in Gd/Fe multilayers

“…5 that the thinner layer as a whole switches on a faster time-scale driven by the AFM exchange which "accelerates" magnetization dynamics, consistent with Ref. 39. The non-monotonic variation of the reversal times of each sublattice with pump fluence is an interesting feature of the reversal processes.…”

“…The initiation of the reversal at the Fe planes furthest from the interface is due to the fact that the presence of Gd at the interface slows the motion of the Fe plane closest to it. The ultrafast demagnetization of Gd has been shown to be much slower than its transition metal counterparts 38 , however, in the presence of antiferromagnetic exchange coupling its demagnetisation rate is decreased 39 . This is consistent with the results of Fig.…”

Multiscale modeling of ultrafast element-specific magnetization dynamics of ferromagnetic alloys

“…From a fundamental viewpoint, however, it is also important to understand the element-specific magnetization dynamics in multielement ferromagnetic alloys. This is challenging from a modeling perspective and, moreover, contradicting results have been observed in NiFe alloys [24][25][26].…”

“…These dynamics were successfully reproduced by Günther et al [25] using the timeresolved magneto-optic Kerr effect in the extreme ultraviolet domain in combination with an infrared pump laser. However, recently Radu et al [26] measured Py in the soft-x-ray regime and obtained different demagnetization rates, with Ni being significantly faster than Fe.…”

Conditions for thermally induced all-optical switching in ferrimagnetic alloys: Modeling of TbCo

“…Finally, we note that the complete set of conditions for the TIMS is still elusive, most likely due to the fact that too many parameters simultaneously play a role in determining the magnetization dynamics, e.g., the exchange, the damping, and the magnetic moments [44]. We believe that in the present work we have made a step forward in this respect by establishing that (i) different demagnetizing rates of the materials and (ii) femtosecond laser pulse durations are necessary conditions.…”