Electrical manipulation of the magnetic order in antiferromagnetic PtMn pillars

Spin-orbit torque switching of an antiferromagnetic metallic heterostructure

“…Our sputtered films, however, have a polycrystalline structure. Previous studies pointed out that significant magnetostriction coefficient 44 and the sensitivity of Mn-based AFMs to crystallinity and/or chemical composition 29,30,32,45 (e.g., effects of Mn substitution/doping and valence electron number) could induce an easy-plane magnetic anisotropy [46][47][48] , resulting in multiple stable Néel vector orientations in the polycrystalline films. Note that our observation of a reversible XMLD contrast along LV and LH configurations ( Fig.…”

“…Note that the current-polarity dependent switching in our PtMn/Pt structures is significantly different from the unipolar characteristics in PtMn/Ru and to those previously observed in AFM-insulator NiO/HM structures [22][23][24]57 , calling for additional factors leading to the observed results. As stated before, a combination of uniaxial and easy-plane anisotropies along with interfacial DMI can lead to the spontaneous multidomain configuration comprising Néel DWs and/or topological spin textures 47,48,[52][53][54] in PtMn/Pt structures. In fact, these predictions have been confirmed by recent experiments demonstrating imprinted antiferromagnetic vortex states on an adjacent ferromagnetic layer in AFM/FM 52,53 or exotic topological meronantimeron pairs in AFM/HM structures 54 .…”

Prospect of Spin-Orbitronic Devices and Their Applications

“…One representative solution is to utilize the current-induced domain wall motion within the FM free layer ( Sengupta et al., 2015a ; Lequeux et al., 2016 ; Yue et al., 2019 ; Yang et al., 2019c ; Siddiqui et al., 2019 ; Azam et al., 2020 ; Zhang et al., 2019b ), for instance, by tuning the pinning potential of FM domain wall motions, SOT-induced multilevel magnetization switching as well as the typical synaptic functionality of spike-timing dependent plasticity (STDP) have been experimentally demonstrated ( Cao et al., 2019 ). Other strategies include the fine-magnetic domain switching in antiferromagnetic (AFM) ( Wadley et al., 2016 ; Olejník et al., 2017 ; Shi et al., 2020 ) or AFM/FM ( Liu et al., 2020b ; Zhou et al., 2020 ; Yun et al., 2020 ) heterostructures where multiple ∼100 nm-sized binary FM domains fixed by the polycrystalline AFM could reverse independently under the applying current ( Fukami et al., 2016 ; Kurenkov et al., 2017 ; Borders et al., 2016 ) and the SOT-induced skyrmion (a topological magnetic state) motions where the number of skyrmions within the signal reading area is proposed to represent the analog synaptic weight ( Song et al., 2020a ). In addition to the above efforts that try to form holistic multilevel magnetization by combining in-plane distributed binary magnetic solitons, which are difficult to achieve scalable multilevel spin-orbitronic synapses, the methodologies of innovating multilevel magnetization with out-of-plane multilevel mechanisms might be more practical and warrant more reliable solutions ( Hong et al., 2018 ; Hu et al., 2020 ; Sheng et al., 2018b ).…”

Electrical manipulation of antiferromagnetic easy axis in IrMn/NiFe exchange-biased structures

“…Wide ranges of AFMs are explored in the bilayer structures, including metallic AFMs of IrMn [26][27][28][29][30] , PtMn 31,32 , and MnN 33 , an insulating AFM of NiO [34][35][36][37] , and a Weyl semimetal AFM of Mn3Sn 38 .…”

“…Notably, AFM switching typically shows multi-level characteristics 17,31 ; the (transverse) resistance of an AFM sample, representing the AFM moment direction, is gradually modulated by the magnitude and polarity of a writing current. This, however, relies on the AFM domain structure because the current-induced SOT controls the overall AFM moments by switching the AFM moment in some domains and/or by driving the AFM domain wall 10,28,32,39 .…”