Abstract
Topological whirls or ‘textures’ of spins such as magnetic skyrmions represent the smallest realizable emergent magnetic entities1,2,3,4,5. They hold considerable promise as robust, nanometre-scale, mobile bits for sustainable computing6,7,8. A longstanding roadblock to unleashing their potential is the absence of a device enabling deterministic electrical readout of individual spin textures9,10. Here we present the wafer-scale realization of a nanoscale chiral magnetic tunnel junction (MTJ) hosting a single, ambient skyrmion. Using a suite of electrical and multimodal imaging techniques, we show that the MTJ nucleates skyrmions of fixed polarity, whose large readout signal—20–70% relative to uniformly magnetized states—corresponds directly to skyrmion size. The MTJ exploits complementary nucleation mechanisms to stabilize distinctly sized skyrmions at zero field, thereby realizing three non-volatile electrical states. Crucially, it can electrically write and delete skyrmions to both uniform states with switching energies 1,000 times lower than the state of the art. Here, the applied voltage emulates a magnetic field and, in contrast to conventional MTJs, it reshapes both the energetics and kinetics of the switching transition, enabling deterministic bidirectional switching. Our stack platform enables large readout and efficient switching, and is compatible with lateral manipulation of skyrmionic bits, providing the much-anticipated backbone for all-electrical skyrmionic device architectures9,10. Its wafer-scale realizability provides a springboard to harness chiral spin textures for multibit memory and unconventional computing8,11.
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Data availability
Source data for the results presented in the paper and Supplementary Information are available at https://oar.a-star.edu.sg/communities-collections/articles/19631. Other relevant data are available from the corresponding author.
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Acknowledgements
We acknowledge helpful discussions with F. Ernult and B. Chen, and experimental inputs from J. Qiu, A. Kumar, P. Chauhan, Y.V. Bhobia, Z. Ma, Y. Niu and W.Y. Gan. This work was supported by the SpOT-LITE programme (grant no. A18A6b0057), funded by Singapore’s RIE2020 initiatives.
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J.L., P.H. and S.L.K.Y. designed the MTJ stack and wafer-level fabrication process, with inputs from H.J.C., S.T.L. and S.C. H.K.T., S.L.K.Y. and Y.T.T. performed the fabrication, aided by R.J.J.L., I.L. and N.C.B.L. S.C. performed the electrical and magnetometry measurements with help from R.J.J.L. and J.Z., and inputs from J.L. and X.C. A.K.J.T. and M.I.S. performed MFM, H.R.T. performed TEM, T.S.S. conducted BLS measurements, and J.H. supported their data analysis. J.H. performed simulations with inputs from X.C. S.C., J.L., P.H., and A.S. wrote the manuscript with inputs from all authors. A.S. coordinated and supervised the work.
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Extended data figures and tables
Extended Data Fig. 1 Schematic of Multilayer Stacks.
Layer-wise structures of the three chiral multilayer stacks studied in this work: (a) full MTJ, (b) companion MTJ, and (c) composite free layer (FL). The SK-MTJ and P-MTJ compositions use different FM thicknesses within the FL (details in Methods).
Extended Data Fig. 2 Field Evolution of FL & SK-MTJ Films.
(a) OP M(H) loop of FL film and corresponding in-field LTEM images (arrow indicates sweep direction, field values indicated). (b) OP M(H) minor loops for SK-MTJ film and corresponding in-field LTEM images (saturated at −1.5 T). Top insets for (a-b) show colour bars indicating the field evolution of magnetic states: uniform magnetization (UM ↑,↓); skyrmion (SK ↑,↓), and labyrinthine stripes (LS).
Extended Data Fig. 3 Field Evolution of SK-MTJ and FL Dots.
MFM images of WDot ≃ 300 nm dot arrays (referenced to positively magnetized tip) for (a-b) SK-MTJ, after (a) −1.5 T saturation, and (b) +1.5 T saturation (flipped x-axis for ease-of-comparison), and (c) FL, respectively. Middle insets show colour bars indicating the field evolution of magnetic states: UM ↑,↓ and SK ↑,↓, respectively (c.f. Extended Data Fig. 2).
Extended Data Fig. 4 Estimation of VCMA Coefficient.
(a, c) Minor R(H) loops acquired on a WCell ≈ 300 nm SK-MTJ, with varying DC bias voltages, VDC of +1 V, 0 V, and −1 V (top to bottom) applied to the TE of the MTJ. (b, d) Variation with VDC of (b) perpendicular energy, E⊥ (represented by shaded regions in a). Red line indicates a linear fit, with extrapolated x-intercept ∼ +3.95 V.
Extended Data Fig. 5 Calculated VCMA Modulation of Skyrmion-to-Uniform Transition Energetics.
(a) GNEB-simulated magnetization images of the skyrmion (SK, left) to uniform state (UM, right) transition at ZF for a WDot = 300 nm FL dot (procedural details in Methods). (b) Energy profiles of the transition with VCMA modulation of the CoFeB (FL(i)) by \({\triangle K}_{{\rm{u}}}^{{\rm{CFB}}}\) = 0 (unchanged) and ±120 kJ/m3. The absolute total energy of the UM state was unchanged with ∆KuCFB (c,d). Evolution of (c) energy barrier, Eb and (d) energy difference, ∆E, with \({\triangle K}_{{\rm{u}}}^{{\rm{CFB}}}\) = 0 varied approximately over the voltage range used for electrical switching (VCMA estimation details in Methods). Coloured markers correspond to the curves in (b).
Extended Data Fig. 6 Bidirectional All-Electrical Switching of SK-MTJ.
(a) MR(H) loop of WCell ≃ 300 nm SK-MTJ (tCo ≃ 1.33 nm) used for switching measurements. (b) Bidirectional AP ↔ SK switching at constant H (−32 to −34 mT, green loops), with SK → AP switching (Vp < 0: left), followed by AP → SK switching (Vp > 0: right). Included for comparison: unidirectional AP → SK switching for varying H (−21 to −32 mT: blue curves). Dashed arrows indicate switching direction, solid asterisks represent MR of switched SK state for Vp ≃ +4.2 V. (c) MFM images at −20 mT, 0 mT, and +20 mT for major (top) and FORC (Hrev = +30 mT) loops (bottom). (d) Final MR of switched SK state (open-red, filled-orange asterisks from b) for varying H, compared to the major MR(H) loop (red, blue) and expected FORC minor loop (dashed orange line, see Fig. 4). Open-red and filled-orange squares indicate MFM-estimated MR for major and FORC (Hrev = +20 mT) loops, respectively.
Extended Data Fig. 7 Skyrmion Motion in FL Wires.
(a) In situ MFM image of 2 × 10 µm FL wire device (stack and fabrication details in Methods) at µ0H ≃ 74 mT. Highlighted box shows region of interest for c-e. (b) Schematic of experimental protocol: current pulses of alternating polarity, J ≃ ±(3.5 − 6.5) × 1011 A/m2, were applied sequentially, and the device was imaged before and after each pulse. (c) Top: representative zoom-in MFM images acquired before and after successive current pulses of opposite polarities (J ≃ 6.3 × 1011 A/m2). Small circles indicate positions of a few representative skyrmions across images; large, dashed circle identifies a prominent defect used for registration. Bottom: tracked positions of skyrmions across pulses (representative skyrmions highlighted), with arrows indicating extent of motion. (d) Polar plot of skyrmion motion statistics for µ0H ≃ 74 mT, compiled for selected J (data for J < 0 rotated by 180◦), showing a spread of velocities and deflections. (e) Plot of the average skyrmion velocity, ⟨vS⟩ against J. Error bars represent standard deviation.
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Supplementary sections 1–12, including Figs. 1–30, Tables 1–3 and References.
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Chen, S., Lourembam, J., Ho, P. et al. All-electrical skyrmionic magnetic tunnel junction. Nature 627, 522–527 (2024). https://doi.org/10.1038/s41586-024-07131-7
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DOI: https://doi.org/10.1038/s41586-024-07131-7
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