SPICE Workshop on Nanomagnetism in 3D, April 30th - May 2nd 2024
Riccardo Tomasello
Magnetic skyrmions are fascinating topological textures with a number of intriguing fundamental and applicative properties. Thanks to the use of the 3rd dimension in magnetic multilayer, the experimental observation of these topological textures has been achieved in the form of skyrmion tubes1. Here, we show the existence of skyrmions in different multilayer systems. First, we show a strategy to distinguish the two typical types of skyrmion tubes, hybrid and pure Néel, based on their applied
filed responses2.The pure Néel skyrmion is characterized by two irreversible phase transitions to labyrinth domains and, subsequently, to skyrmions with opposite polarity. Whereas, the hybrid skyrmion exhibits a reversible phase transition to larger skyrmions. The identification of the type of skyrmion is crucial for skyrmion dynamics3.
Second, we prove the stabilization of two distinct skyrmion phases in a novel hybrid ferromagnetic/ferrimagnetic multilayer4. We identify one skyrmion which goes through the whole thickness of the multilayer – tubular skyrmion – and another one which exists only in the external ferromagnetic multilayers but not in the internal ferrimagnetic material – incomplete skyrmion. The
two skyrmions exhibit very distinct MFM contrasts, and this can be used to code the different
information bit in a racetrack memory.
Eventually, we deal with the achievement of skyrmions in a magnetic tunnel junction (MTJ)5. We design an innovative system where a standard multilayer is coupled with a standard CoFeB-based MTJ. In particular, the multilayer acts as “skyrmion generator” for the MTJ free layer. We can measure a TMR of about 20%, and each skyrmion provide a resistance change of about 50 . The
existence of skyrmions in MTJ paves the way to applications, such as skyrmion oscillators, detectors, memristors, which are still only theorized.
1. Li et al. Adv. Mater. 31, 1807683 (2019).
2. Tomasello et al., Phys. Rev. B 107, 184416 (2023).
3. Wang et al. Nat. Electron. 3, 672–679 (2020).
4. Mandru et al. Nat. Commun. 11, 6365 (2020); Yıldırım et al., Appl. Mater. Inter. 14, 34002 (2022).
5. Guang et al. Adv. Electron. Mater. 9, 2200570 (2023).