Optimal Control Drives Ultrafast and Energy-Efficient Magnetization Switching in Van der Waals Magnets.

Abstract

The accelerating expansion of data-centric technologies is sharply increasing the energy burden of information storage, placing unprecedented pressure on the efficiency of magnetic switching. Conventional field-driven reversal, once the foundation of magnetic memory, has become impractical in modern architectures due to its high energy cost, limited spatial selectivity, and poor scalability, leading to the dominance of current-driven techniques based on spin-transfer- and spin-orbit-torque (STT, SOT). Here we show that optimal control theory (OCT) enables precisely shaped magnetic-field pulses that unlock ultrafast, deterministic, and exceptionally energy-efficient magnetization switching in van der Waals magnets, making field-driven reversal competitive with, and in some regimes superior to, established current-based approaches. Using <math xmlns="http://www.w3.org/1998/Math/MathML"> <semantics> <mrow><msub><mi>Fe</mi> <mn>3</mn></msub> <msub><mi>GaTe</mi> <mn>2</mn></msub> </mrow> <annotation>${\rm Fe}_3{\rm GaTe}_2$</annotation></semantics> </math> , <math xmlns="http://www.w3.org/1998/Math/MathML"> <semantics> <mrow><msub><mi>Fe</mi> <mn>3</mn></msub> <msub><mi>GeTe</mi> <mn>2</mn></msub> </mrow> <annotation>${\rm Fe}_3{\rm GeTe}_2$</annotation></semantics> </math> , and CrSBr as representative systems, we show that OCT-induced uniform spin rotations completed within the picosecond range ( <math xmlns="http://www.w3.org/1998/Math/MathML"> <semantics><mrow><mn>1</mn> <mo>-</mo> <mn>10</mn></mrow> <annotation>$1-10$</annotation></semantics> </math> ps) with switching energies ( <math xmlns="http://www.w3.org/1998/Math/MathML"> <semantics><mrow><mn>9.7</mn> <mo>-</mo> <mn>0.94</mn></mrow> <annotation>$9.7-0.94$</annotation></semantics> </math> nJ) up to two orders of magnitude lower than conventional field protocols ( <math xmlns="http://www.w3.org/1998/Math/MathML"> <semantics><mrow><mn>91.2</mn> <mo>-</mo> <mn>42.8</mn></mrow> <annotation>$91.2-42.8$</annotation></semantics> </math> nJ). Optimized fields operate at amplitudes more than tenfold smaller than standard methods, and by exploiting material-specific parameters such as damping and anisotropy, low femtojoule switching energies become attainable, surpassing SOT or STT schemes. Our findings suggest that, rather than being obsolete, OCT-field implementations could complement or hybridize with current- and light-driven approaches, opening a new design space where magnetic switching is tailored by the interplay of fields, currents, and photons to achieve unprecedented efficiency, speed, and scalability.