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The motive of the research is to develop multi-level magnetic memory using multi-state magnetic structures, which can be manipulated using spin-orbit torques. The multi-state magnetic structures are fabricated using multiple crossing ellipses. We showed that “N” crossing ellipses (where N = 1, 2, 3, 4, 5) can be stabilized in 2N number of discrete remanent states by applying (and removing) external magnetic field [1-3]. The field-free switchings between the remanent states have been performed by spin-orbit torques which is generated by flowing current in the adjacent heavy metal layer. Second harmonic Hall measurements along with micro-magnetic simulations reveal that switching is dominated by Slonczewski torque and occurred via domain wall propagation [2]. Further manipulating individual ellipse of N crossing ellipses structures by spin-orbit torques, the number of states grows to 2N, and when each arm of individual ellipse manipulated separately the number of remanent states jump to 22N, including the states which consists of a π-type Néel domain wall in the overlap area [3]. So in principle, two, three and four crossing ellipses can be stabilized in 16, 64 and 256 distinct states, respectively. Considering such large number of states in a relatively simple structures and the ability to switch between them by spin orbit torques in absence of any external magnetic field make such structures extremely viable for various spintronics applications; such as multi-level MRAM and neuromorphic computing etc. Further, we fabricate a magnetic tunnel junction using a single ellipse and a two crossing ellipses as ferromagnetic layers on top of a heavy metal layer [4]. The MTJ exhibits four distinct states corresponding to the four remanent states of two crossing ellipses structure. The field-free reversible switchings between the states of magnetic tunnel junction are performed by spin-orbit torques [4]. We believe that the demonstrated four-states MTJ is important steps towards fabricating multi-level MTJ with numerous numbers of states.
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