Using micromagnetic simulations, we demonstrate the tilted perpendicular anisotropy-induced spin-orbit ratchet effect. In spin-orbit torque(SOT)-induced magnetization switching, the critical currents required to switc...Using micromagnetic simulations, we demonstrate the tilted perpendicular anisotropy-induced spin-orbit ratchet effect. In spin-orbit torque(SOT)-induced magnetization switching, the critical currents required to switch between the two magnetization states(upward and downward magnetization) are asymmetric. In addition, in the nanowire structure, tilted anisotropy induces formation of tilted domain walls(DWs). The tilted DWs exhibit a ratchet behavior during motion. The ratchet effect during switching and DW motions can be tuned by changing the current direction with respect to the tilting direction of anisotropy. The ratchet motion of the DWs can be used to mimic the leaky-integrate-fire function of a biological neuron, especially the asymmetric property of the “potential” and “reset” processes. Our results provide a full understanding of the influence of tilted perpendicular anisotropy on SOT-induced magnetization switching and DW motion, and are beneficial for designs of further SOT-based devices.展开更多
Magnetic bubbles have again become a subject of significant attention following the experimental observation of topologically nontrivial magnetic skyrmions. In recent work, tailoring the shape of the bubbles is consid...Magnetic bubbles have again become a subject of significant attention following the experimental observation of topologically nontrivial magnetic skyrmions. In recent work, tailoring the shape of the bubbles is considered a key factor for their dynamics in spintronic devices. In addition to the reported circular, elliptical, and square bubbles, here we observe triangular bubble domains in bismuth-doped yttrium iron garnet(Bi-YIG) using Kerr microscopy. The bubble domains evolve from discrete circular to latticed triangular and hexagonal shapes. Further, the orientation of the triangular bubbles in the hexagonal lattices can be flipped by decreasing the magnetic field. The sixfold in-plane magnetic anisotropy of Bi-YIG(111) crystal, which is presumably the mechanism underlying the triangular shape of the bubbles, is measured as1179 erg/cm~3. The study of the morphologies of topologically trivial bubbles in YIG offers insight into nontrivial spin textures, which is appealing for future spintronic applications.展开更多
Precise and ultrafast control over photo-induced charge currents across nanoscale interfaces could lead to important applications in energy harvesting,ultrafast electronics,and coherent terahertz sources.Recent studie...Precise and ultrafast control over photo-induced charge currents across nanoscale interfaces could lead to important applications in energy harvesting,ultrafast electronics,and coherent terahertz sources.Recent studies have shown that several relativistic mechanisms,including inverse spin-Hall effect,inverse Rashba–Edelstein effect,and inverse spin-orbit-torque effect,can convert longitudinally injected spinpolarized currents from magnetic materials to transverse charge currents,thereby harnessing these currents for terahertz generation.However,these mechanisms typically require external magnetic fields and exhibit limitations in terms of spin-polarization rates and efficiencies of relativistic spin-to-charge conversion.We present a nonrelativistic and nonmagnetic mechanism that directly utilizes the photoexcited high-density charge currents across the interface.We demonstrate that the electrical anisotropy of conductive oxides RuO2 and IrO2 can effectively deflect injected charge currents to the transverse direction,resulting in efficient and broadband terahertz radiation.Importantly,this mechanism has the potential to offer much higher conversion efficiency compared to previous methods,as conductive materials with large electrical anisotropy are readily available,whereas further increasing the spin-Hall angle of heavy-metal materials would be challenging.Our findings offer exciting possibilities for directly utilizing these photoexcited high-density currents across metallic interfaces for ultrafast electronics and terahertz spectroscopy.展开更多
The ability to generate and manipulate broadband chiral terahertz waves is essential for applications in material imaging,terahertz sensing,and diagnosis.It can also open up new possibilities for nonlinear terahertz s...The ability to generate and manipulate broadband chiral terahertz waves is essential for applications in material imaging,terahertz sensing,and diagnosis.It can also open up new possibilities for nonlinear terahertz spectroscopy and coherent control of chiral molecules and magnetic materials.The existing methods,however,often suffer from low efficiency,narrow bandwidth,or poor flexibility.Here,we propose a novel type of laser-driven terahertz emitters,consisting of metasurface-patterned magnetic multilayer heterostructures,that can overcome the shortcomings of the conventional approaches.Such hybrid terahertz emitters combine the advantages of spintronic emitters for being ultrabroadband,efficient,and highly flexible,as well as those of metasurfaces for the powerful control capabilities over the polarization state of emitted terahertz waves on an ultracompact platform.Taking a stripe-patterned metasurface as an example,we demonstrate the efficient generation and manipulation of broadband chiral terahertz waves.The ellipticity can reach>0.75 over a broad terahertz bandwidth(1 to 5 THz),representing a high-quality and efficient source for few-cycle circularly polarized terahertz pulses with stable carrier waveforms.Flexible control of ellipticity and helicity is also demonstrated with our systematic experiments and numerical simulations.We show that the terahertz polarization state is dictated by the interplay between laser-induced spintronic-origin currents and the screening charges/currents in the metasurfaces,which exhibits tailored anisotropic properties due to the predesigned geometric confinement effects.Our work opens a new pathway to metasurface-tailored spintronic emitters for efficient vector-control of electromagnetic waves in the terahertz regime.展开更多
A high-sensitivity DC magneto-optical Kerr effect(MOKE)apparatus is described in this Letter.Via detailed analysis on several dominatingnoise sources,we have proposed solutions that significantly lower the MOKE noise,...A high-sensitivity DC magneto-optical Kerr effect(MOKE)apparatus is described in this Letter.Via detailed analysis on several dominatingnoise sources,we have proposed solutions that significantly lower the MOKE noise,and a sensitivity of 1.5×10^(-7)rad/√Hz is achieved with long-term stability.The sensitivity of the apparatus is tested by measuring a wedgeshaped Ni thin film on SiO_(2)with Ni thickness varying from 0 to 3 nm.A noise floor of 1.5×10^(-8)rad is demonstrated.The possibility of further improving sensitivity to 10^(-9)rad via applying AC modulation is also discussed.展开更多
L1_(0)-FePt distinguishes itself for its ultrahigh perpendicular magnetic anisotropy(PMA),enabling thermally stabile memory cells to scale down to 3 nm.The recently discovered“bulk”spin−orbit torques in L1_(0)-FePt ...L1_(0)-FePt distinguishes itself for its ultrahigh perpendicular magnetic anisotropy(PMA),enabling thermally stabile memory cells to scale down to 3 nm.The recently discovered“bulk”spin−orbit torques in L1_(0)-FePt provide an efficient and scalable way to manipulate the L1_(0)-FePt magnetization.However,the existence of an external field during the switching limits its practical application,and therefore field-free switching of L1_(0)-FePt is highly demanded.In this manuscript,by growing the L1_(0)-FePt film on vicinal MgO(001)substrates,we realize the field-free switching of L1_(0)-FePt.This method is different from previously established strategies as it does not need to add other functional layers or create asymmetry in the film structure.The dependence on the vicinal angle,film thickness,and growth temperature demonstrates a wide operation window for the fieldfree switching of L1_(0)-FePt.We confirm the physical origin of the field-free switching is due to the tilted anisotropy of L1_(0)-FePt induced by the vicinal surface.We also quantitatively characterize the spin-orbit torques in the L1_(0)-FePt films.Our results extend beyond the established strategies to realize field-free switching,and potentially could be applied to mass production.展开更多
基金supported by the National Natural Science Foundation of China (Grant No.12274108)the Natural Science Foundation of Zhejiang Province (Grant Nos.LY23A040008 and LY23A040008)the Basic Scientific Research Project of Wenzhou (Grant No.G20220025)。
文摘Using micromagnetic simulations, we demonstrate the tilted perpendicular anisotropy-induced spin-orbit ratchet effect. In spin-orbit torque(SOT)-induced magnetization switching, the critical currents required to switch between the two magnetization states(upward and downward magnetization) are asymmetric. In addition, in the nanowire structure, tilted anisotropy induces formation of tilted domain walls(DWs). The tilted DWs exhibit a ratchet behavior during motion. The ratchet effect during switching and DW motions can be tuned by changing the current direction with respect to the tilting direction of anisotropy. The ratchet motion of the DWs can be used to mimic the leaky-integrate-fire function of a biological neuron, especially the asymmetric property of the “potential” and “reset” processes. Our results provide a full understanding of the influence of tilted perpendicular anisotropy on SOT-induced magnetization switching and DW motion, and are beneficial for designs of further SOT-based devices.
基金support by the National Natural Science Foundation of China (Grant Nos. 52061135105 and 12074025)support by the National Natural Science Foundation of China (Grant Nos. 11974079, 12274083, and 12221004)the Shanghai Municipal Science and Technology Basic Research Project (Grant No. 22JC1400200)。
文摘Magnetic bubbles have again become a subject of significant attention following the experimental observation of topologically nontrivial magnetic skyrmions. In recent work, tailoring the shape of the bubbles is considered a key factor for their dynamics in spintronic devices. In addition to the reported circular, elliptical, and square bubbles, here we observe triangular bubble domains in bismuth-doped yttrium iron garnet(Bi-YIG) using Kerr microscopy. The bubble domains evolve from discrete circular to latticed triangular and hexagonal shapes. Further, the orientation of the triangular bubbles in the hexagonal lattices can be flipped by decreasing the magnetic field. The sixfold in-plane magnetic anisotropy of Bi-YIG(111) crystal, which is presumably the mechanism underlying the triangular shape of the bubbles, is measured as1179 erg/cm~3. The study of the morphologies of topologically trivial bubbles in YIG offers insight into nontrivial spin textures, which is appealing for future spintronic applications.
基金the support from the National Key Research and Development Program of China (Grant No. 2022YFA1404700)the support from the National Key Research and Development Program of China (Grant No. 2021YFA1400200)+7 种基金the support from the National Natural Science Foundation of China (Grant No. 12221004)the support from the National Natural Science Foundation of China (Grant No. 12174028)the support from the National Natural Science Foundation of China (Grant No. 12274091)the National Natural Science Foundation of China (Grant Nos. 11974079 and 12274083)the support from the Shanghai Municipal Science and Technology Basic Research Project (Grant No. 22JC1400200)the support from the National Key Research Program of China (Grant No. 2022YFA1403300)the Shanghai Municipal Science and Technology Major Project (Grant No. 2019SHZDZX01)the support from the Natural Science Foundation of Shanghai (Grant No. 20JC1414601)
文摘Precise and ultrafast control over photo-induced charge currents across nanoscale interfaces could lead to important applications in energy harvesting,ultrafast electronics,and coherent terahertz sources.Recent studies have shown that several relativistic mechanisms,including inverse spin-Hall effect,inverse Rashba–Edelstein effect,and inverse spin-orbit-torque effect,can convert longitudinally injected spinpolarized currents from magnetic materials to transverse charge currents,thereby harnessing these currents for terahertz generation.However,these mechanisms typically require external magnetic fields and exhibit limitations in terms of spin-polarization rates and efficiencies of relativistic spin-to-charge conversion.We present a nonrelativistic and nonmagnetic mechanism that directly utilizes the photoexcited high-density charge currents across the interface.We demonstrate that the electrical anisotropy of conductive oxides RuO2 and IrO2 can effectively deflect injected charge currents to the transverse direction,resulting in efficient and broadband terahertz radiation.Importantly,this mechanism has the potential to offer much higher conversion efficiency compared to previous methods,as conductive materials with large electrical anisotropy are readily available,whereas further increasing the spin-Hall angle of heavy-metal materials would be challenging.Our findings offer exciting possibilities for directly utilizing these photoexcited high-density currents across metallic interfaces for ultrafast electronics and terahertz spectroscopy.
基金support from the National Key Research and Development Program of China (Grant No.2017YFA0303504)the National Natural Science Foundation of China(Grant No.11734007)+8 种基金the Natural Science Foundation of Shanghai(Grant No.20JC1414601)support from the National Natural Science Foundation of China(Grant Nos.11734006 and 11974079)the National Key Research and Development Program of China(Grant No.2016YFA0300703)the Shanghai Municipal Science and Technology Major Project(Grant No.2019SHZDZX01)financial support from the National Natural Science Foundation of China(Grant No.11874121)the Shanghai Municipal Science and Technology Basic Research Project(Grant No.19JC1410900)support from the National Natural Science Foundation of China(Grant No.11874123)the Shanghai Science and Technology Committee(Grant No.20ZR1406000)the Alexander von Humboldt Foundation for support.
文摘The ability to generate and manipulate broadband chiral terahertz waves is essential for applications in material imaging,terahertz sensing,and diagnosis.It can also open up new possibilities for nonlinear terahertz spectroscopy and coherent control of chiral molecules and magnetic materials.The existing methods,however,often suffer from low efficiency,narrow bandwidth,or poor flexibility.Here,we propose a novel type of laser-driven terahertz emitters,consisting of metasurface-patterned magnetic multilayer heterostructures,that can overcome the shortcomings of the conventional approaches.Such hybrid terahertz emitters combine the advantages of spintronic emitters for being ultrabroadband,efficient,and highly flexible,as well as those of metasurfaces for the powerful control capabilities over the polarization state of emitted terahertz waves on an ultracompact platform.Taking a stripe-patterned metasurface as an example,we demonstrate the efficient generation and manipulation of broadband chiral terahertz waves.The ellipticity can reach>0.75 over a broad terahertz bandwidth(1 to 5 THz),representing a high-quality and efficient source for few-cycle circularly polarized terahertz pulses with stable carrier waveforms.Flexible control of ellipticity and helicity is also demonstrated with our systematic experiments and numerical simulations.We show that the terahertz polarization state is dictated by the interplay between laser-induced spintronic-origin currents and the screening charges/currents in the metasurfaces,which exhibits tailored anisotropic properties due to the predesigned geometric confinement effects.Our work opens a new pathway to metasurface-tailored spintronic emitters for efficient vector-control of electromagnetic waves in the terahertz regime.
基金support from the National Natural Science Foundation of China(Nos.12125403 and 11874123)the Shanghai Science and Technology Committee(No.20ZR1406000)。
文摘A high-sensitivity DC magneto-optical Kerr effect(MOKE)apparatus is described in this Letter.Via detailed analysis on several dominatingnoise sources,we have proposed solutions that significantly lower the MOKE noise,and a sensitivity of 1.5×10^(-7)rad/√Hz is achieved with long-term stability.The sensitivity of the apparatus is tested by measuring a wedgeshaped Ni thin film on SiO_(2)with Ni thickness varying from 0 to 3 nm.A noise floor of 1.5×10^(-8)rad is demonstrated.The possibility of further improving sensitivity to 10^(-9)rad via applying AC modulation is also discussed.
基金This work was supported by the“Pioneer”and“Leading Goose”RD Program of Zhejiang Province(Grant No.2022C01053)the National Natural Science Foundation of China(Grant No.12274108,11874135 and 12104119)+1 种基金the Key Research and Development Program of Zhejiang Province(Grant No.2021C01039)the Natural Science Foundation of Zhejiang Province,China(Grant Nos.LQ20F040005 and LQ21A050001).
文摘L1_(0)-FePt distinguishes itself for its ultrahigh perpendicular magnetic anisotropy(PMA),enabling thermally stabile memory cells to scale down to 3 nm.The recently discovered“bulk”spin−orbit torques in L1_(0)-FePt provide an efficient and scalable way to manipulate the L1_(0)-FePt magnetization.However,the existence of an external field during the switching limits its practical application,and therefore field-free switching of L1_(0)-FePt is highly demanded.In this manuscript,by growing the L1_(0)-FePt film on vicinal MgO(001)substrates,we realize the field-free switching of L1_(0)-FePt.This method is different from previously established strategies as it does not need to add other functional layers or create asymmetry in the film structure.The dependence on the vicinal angle,film thickness,and growth temperature demonstrates a wide operation window for the fieldfree switching of L1_(0)-FePt.We confirm the physical origin of the field-free switching is due to the tilted anisotropy of L1_(0)-FePt induced by the vicinal surface.We also quantitatively characterize the spin-orbit torques in the L1_(0)-FePt films.Our results extend beyond the established strategies to realize field-free switching,and potentially could be applied to mass production.