Spintronic control of magnetostatically coupled dot assemblies

Author / Creator

MMM 2020 (2020)

Conferences

MMM 2020 R3: MRAM, Magnetic Logic, and Related Devices (2020)

Available as

Online

Summary

Magnetostatically coupled monodomain patterns have been studied for use as cellular automata and logic gates [1, 2]. Here the external magnetic field clocked switching is deterministic, and the mag...

Magnetostatically coupled monodomain patterns have been studied for use as cellular automata and logic gates [1, 2]. Here the external magnetic field clocked switching is deterministic, and the magneto-optic Kerr (MOKE) effect microscopy or magnetic force microscopy (MFM) characterization only detects slow dynamics. We investigate similar systems, but with the use of spintronics for fast, all-electronic control and measurement. This is relevant both for low power magnetic logic, and for detection of fast dynamics in coupled superparamagnets that could be used in reservoir computing. We have demonstrated the ability to deterministically switch the state of a magnetic tunnel junction (MTJ) using spin orbit torque (SOT) [3], and this is used to switch the control dot at the beginning of the coupled patterns (Fig.1a). We have also detected magnetization changes in patterned nanodot MTJs using tunnel magnetoresistance (TMR) and a conductive atomic force microscopy (C-AFM) probe tip [4], and this is used to detect the dot magnetization at different locations. The dots were patterned by E-beam lithography from an MTJ thin film stack with a 3 nm thick CoFeB free layer. Fig.1b shows the schematic for a control dot and a neighboring secondary dot. Mumax3 simulations were conducted to match the magnetic field generated by the control dot with the coercive field of the secondary dot to facilitate the signal processing in magnetically coupled dots [5]. Fig.2 shows the magnetic field profile along +x direction. Inside the secondary dot, the magnetic field ranged from 2 to 15 mT, comparable to the 8 mT coercive field of the secondary dot, as shown in the Fig.2 inset. This ensures us that we could propagate a signal inside magnetically coupled dots. C-AFM measurements test the predicted switching and propagation along the nanodot chain of Fig.1.References: 1. R. P. Cowburn and M. E. Welland, Science 287 1466 (2000). 2. A. Imre, et al., Science 311 205 (2006). 3. M. Bapna, et al., Phys. Rev. Applied 10, 024013 (2018). 4. B.Parks, et al., Phys. Rev. Applied 13, 014063 (2020). 5. A. Vansteenkiste et al., AIP Adv. 4, 107133 (2014).

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