Ultrafast Racetrack Based on Compensated Co/Gd‐Based Synthetic Ferrimagnet with All‐Optical Switching

Abstract

the Dzyaloshinskii-Moriya interaction (DMI) [6][7][8] with synthetic antiferromagnets (SAFs), which resulted in reported DW velocities close to 750 m s -1 . [9] Despite the large improvement, the energy efficiency is still limited due to the weak strength of the antiferromagnetic (AF) coupling. Therefore, the materials platform of rare earth (RE)-transition metal (TM) compounds garnered considerable attention, [1] promising faster CIDWM due to the much stronger direct AF coupling than the indirect exchange coupling [10] utilized in SAFs. Furthermore, the SOTs used to drive the DW promise to be highly efficient in the RE-TM systems as a result of the long spin coherence length. [11] Cosequently, high velocity CIDWM has been reported in Co-Gdbased ferrimagnetic alloy systems [12,13] when the angular momentum in the magnetic material is compensated, being at least a factor of three faster than that of the previously reported SAFs.Besides the efficient CIDWM, single pulse all-optical switching (AOS) of the magnetization [14,15] in the RE-TM systems has obtained significant attention thanks to its subpicosecond [16] energy efficient [14,17,18] magnetization switching enabled by the ultrafast angular momentum transfer upon laser excitation. [19] This can be useful as a new generation of ultrafast magnetic memory, as well as a data buffer between electronics and integrated photonics. [14,20,21] Recently, a synthetic ferrimagnetic system based on a Pt/Co/Gd- [18,22] layered structure has shown high robustness [23] for such a hybrid integration. These kinds of synthetic ferrimagnets have some distinct advantages over RE-TM alloys. For instance, AOS is not limited by the exact composition. [24] They also withstand thermal annealing [25] and offer easier magnetic composition control at wafer scale than the alloy system, as well as better access to interface engineering. Therefore, it has been proposed that such a materials platform has high potential to realize a hybrid integration of DW memory in photonic platforms to further enhance their storage density. [20,26] So far, the CIDWM of Co/Gd bilayers [26,27] has been investigated. However, the highest reported velocity, achieved at cryogenic conditions, [27] was several times lower than that reported in alloys, [12] in part due to large net angular momentum, low compensation temperature as well as DW pinning effects. In this report, we therefore propose a materials platform based on the [Co/Gd] 2 synthetic ferrimagnet capable of accommodating both efficient CIDWM of over 2 km s -1 ) at room temperature

Exploring THz exchange resonances in synthetic ferrimagnets with ultrashort optically induced spin currents

“…Additionally, ultrafast domain wall motion close to the compensation point of angular momentum has been observed very recently [27]. The coexistence of these properties makes this material a promising candidate for hybrid spintronic-photonic memory applications [27,28].…”

“…Co/Gd multilayers are highly relevant for a variety of spintronic applications as they exhibit energy-efficient single-shot all-optical magnetization switching [26]. Additionally, ultrafast domain wall motion close to the compensation point of angular momentum has been observed very recently [27]. The coexistence of these properties makes this material a promising candidate for hybrid spintronic-photonic memory applications [27,28].…”

Ultralow Power and Shifting-Discretized Magnetic Racetrack Memory Device Driven by Chirality Switching and Spin Current

“…3 Due to its nonvolatility, high storage capacity, fast speed, and flexible design, it has huge application potential at various levels in the on-chip memory hierarchy. 4,5 Over the past decades, the racetrack memory has evolved 6 rapidly in terms of density, 7 speed, 8 and write energy 9 by employing more efficient spin torques or novel film structures. Regardless of the application direction, however, there are still several challenges before domain wall (DW) devices become commercially available.…”

“…Nonvolatile memory, a type of computer storage that retains data even when the power is turned off, is an important and hot research direction for ultralow power consumption and high density storage today. , Among these memories, magnetic racetrack memory, in which a train of up and down magnetic bits is moved electrically along a magnetic track, has become the research focus of spintronic community since its first experimental demonstration . Due to its nonvolatility, high storage capacity, fast speed, and flexible design, it has huge application potential at various levels in the on-chip memory hierarchy. , Over the past decades, the racetrack memory has evolved rapidly in terms of density, speed, and write energy by employing more efficient spin torques or novel film structures. Regardless of the application direction, however, there are still several challenges before domain wall (DW) devices become commercially available.…”

Magnetostatics of room temperature compensated Co/Gd/Co/Gd-based synthetic ferrimagnets

“…[17][18][19] Interestingly, the combination of AOS and efficient CIDWM in this material system is also very promising to bridge the gap between photonics and spintronics. 6,[20][21][22] Co/Gd-based synthetic ferrimagnetic bilayers, where the 3d and 4f-materials are grown as discrete layers, have a few distinct advantages over 3d-4f alloys. The layered structure of these synthetic ferrimagnets allows for easier adaptation to wafer scale production.…”