Theoretical methods of femtomagnetism and ultrafast spintronics

Today’s society is based on the processing and storage of large amounts of data. The urgent need for increased data storage capacity and the rapid energy consumption of data centers require the optimization and innovation of magnetic data storage devices, in which data is stored with the orientation of tiny magnetic regions. Specifically, the goal is to reduce power consumption and allow higher data read and write speeds.

For his Ph.D. research, Maarten Beens discovered that the use of very short laser pulses is a promising candidate for developing faster magnetic memory devices.

Femtomagnetism

The research field that focuses on controlling magnetic order with ultrashort (femtosecond) laser pulses is referred to as femtomagnetism. The field emerged in the late 1990s when it was discovered that when excited by a laser pulse, the magnetization of a magnetic thin film changes surprisingly quickly and is extinguished within a trillionth of a second.

Later, it was shown that laser pulses can be used to change the direction of magnetization in certain types of magnetic alloys, a phenomenon called all-optical switching (AOS). Since it provides a way to direct the magnetic order from a “0” state to a “1” state, the AOS discovery proved that phemomagnetism can lead to the development of innovative data recording technologies.

More recent studies show that the control of magnetism with laser pulses goes beyond influencing at the local level and can be used to create so-called “spin currents” that allow magnetization to be manipulated over a finite distance. Here, “spin” refers to the elementary magnetic property of an electron. The procedures listed create several opportunities to create a robust and reliable data recording scheme.

Building on the past

In order to realize the full applicability of phemomagnetism in future memory devices, an understanding of the aforementioned phenomena at the microscopic level is required. In his Ph.D. research, Maarten Beens and his collaborators build on the theoretical principles developed in recent decades and present new insights into the mechanisms behind ultrafast magnetism.

For example, the mathematical models developed by Beens and colleagues result in a better understanding of the connection between local damping of magnetization and the generation of spin currents. In agreement with recent experimental studies, it was shown that the two processes appear to have the same physical origin. Here, the key components are the heating caused by the laser pulse and the subsequent wave-like magnetic excitations generated inside the magnet.

In addition, Beens developed a theoretical model that makes it possible to compare the various magnetic material systems that enable all-optical switching. A double layer consisting of a cobalt layer and a gadolinium layer proved to be an ideal candidate with respect to the robustness and reliability of the switching process. The layered structure allows a relatively simple way to tune the magnetic characteristics of the entire system so that the material properties critical to the AOS process can be optimized.

In addition, the clever engineering of the magnetic stacks allows the generated spin currents to play a role in assisting the switching process. Results Been’s simulations highlight that the use of femtosecond laser pulses remains a promising data recording tool for future magnetic memory devices. However, the underlying physics is still not fully understood and needs to be further investigated in the coming years to determine its full potential.