Integration of single-shot all-optical switching Tb/Co multilayer-based electrodes within perpendicular magnetic tunnel junctions INVITED

Author / Creator

MMM 2020 (2020)

Conferences

MMM 2020 P2: Magnetic Recording via Optical, Heat and Magnetic Excitation II (2020)

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Online

Summary

Since the observation of all-optical switching of magnetization in the ferrimagnetic alloy GdFeCo using femtosecond laser pulses, there has been a significant interest in exploiting this switching ...

Since the observation of all-optical switching of magnetization in the ferrimagnetic alloy GdFeCo using femtosecond laser pulses, there has been a significant interest in exploiting this switching process for data recording [1]. The ultrafast speed of the magnetization switching allows to push the writing speeds of magnetic memories towards THz frequencies. A first approach for the exploitation of all-optical switching in spintronic devices was explored by Chen et al. [2] on optically switchable GdFeCo layer integrated within a microsized magnetic tunnel junction pillar. In this talk we will discuss the recent advances on the development of perpendicular magnetic tunnel junctions incorporating [Tb/Co]-CoFeB electrodes whose magnetization can be optically controlled via helicity-independent single-shot switching. The ultrafast optical control of the magnetization in this system gives rise to capabilities to be exploited as a storage layer in a magnetic tunnel junction. Within our results we will highlight a first evidence of helicity-independent all-optical switching in a [Co/Tb] multilayered-based system coupled to CoFeB layers with both ps- and fs-long single laser pulses. We also explore the magneto-optical properties of multilayers and their thermal stability upon different annealing temperatures. The magneto optical response and the perpendicular magnetic anisotropy of our system was achieved even after annealing at 250°C. The laser pulse duration and fluence dependence for the CoFeB/[Tb/Co]5 electrodes were explored using single 70fs and 7ps laser pulses with fluences F = 3.1, 3.5 and 4.0mJ/cm2. As can be seen from Fig.1, images obtained for a laser pulse duration D = 7ps and 70fs, a clear magnetization reversal can be achieved for F = 3.5mJ/cm2. Results also determined that reducing the pulse duration to 70fs, the fluence required to induce thermal demagnetization on the sample increases. Our all-optical switching electrodes FeCoB/Ta/[Tb/Co]N were finally integrated into a magnetic tunnel junction. Electrical evaluation of nanopatterned AOS-MTJ showed TMR ratios up to 36 % depending on the diameter of the junctions and on the number of repetitions of the [Tb/Co] bilayers. The full structure of the junctions consist of: Ta(30Å)/FeCoB(11Å)/MgO(23Å)/FeCoB(13Å)/Ta(2Å)/[Tb(9.5Å)/Co(12.5Å)]5. The TMR values distribution of hundreds of MTJ with different diameters is shown in Fig. 2a. The maximum TMR ratio (36 %) was observed for a 200 nm-diameter junction with a minimum resistance of 6 kΩ. Fig. 2b shows the corresponding Resistance loop extracted from the 200 nm-diameter (yellow) distribution of Fig. 2a. To our knowledge, we are presenting the first study that reports the helicity-independent all-optical switching in a Co/Tb multilayered-based system. The integration of optically switchable electrodes within magnetic tunnel junctions is a key step towards future spintronic technologies. In this direction, the research presented here, related to the nanofabrication of high TMR ratio-magnetic tunnel junction using [Co/Tb]-CoFeB electrodes, are a contribution that can lead to substantial advances in hybrid spintronic-photonic devices and contribute to the development of magnetic tunnel junctions with new functionalities, particularly the ability to control the magnetization of the storage layer with ultrafast laser pulses. This research has received funding from the European Union's Horizon 2020 research and innovation program under FET-Open Grant Agreement No. 713481 SPICE.References: 1. A. V. Kimel et al. Nat. Mater. 13 225 (2014) 2. J. Y. Chen et al. Phys. Rev. Appl. 7 021001 (2017) 3. L. Avilés-Félix et al. Sci. Rep. 10 5211 (2020). 4. L. Avilés-Félix, et al. AIP Advances 9, 125328 (2019) 5. A. Olivier et al. Accepted in IOP Nanotechnology (2020)

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