Pub Date : 2024-08-02DOI: 10.1038/s44306-024-00045-0
Taekoo Oh, Naoto Nagaosa
Spin–orbit coupling is a relativistic effect coupling the orbital angular momentum with the spin, which determines the physical properties of condensed matter. For instance, the spin–orbit coupling strongly influences spin dynamics, opening the possibility for promising applications. The topological insulator–ferromagnet heterostructure is a typical example exhibiting spin dynamics driven by current-induced spin–orbit torque. Recent observations of the sign flip of Hall conductivity imply that the spin–orbit torque is strong enough to flip magnetization within this heterostructure. Motivated by this, our study elucidates the conditions governing spin flips by studying the magnetization dynamics. We establish that the interplay between spin-anisotropy and spin–orbit torque plays a crucial role in the magnetization dynamics. Furthermore, we categorize various modes of magnetization dynamics, constructing a comprehensive phase diagram across distinct energy scales, damping constants, and applied frequencies. We also consider the effect of a magnetic field on the magnetization dynamics. This research not only offers insights into controlling spin direction but also charts a new pathway to the practical application of spin–orbit coupled systems.
{"title":"Unraveling the dynamics of magnetization in topological insulator-ferromagnet heterostructures via spin-orbit torque","authors":"Taekoo Oh, Naoto Nagaosa","doi":"10.1038/s44306-024-00045-0","DOIUrl":"10.1038/s44306-024-00045-0","url":null,"abstract":"Spin–orbit coupling is a relativistic effect coupling the orbital angular momentum with the spin, which determines the physical properties of condensed matter. For instance, the spin–orbit coupling strongly influences spin dynamics, opening the possibility for promising applications. The topological insulator–ferromagnet heterostructure is a typical example exhibiting spin dynamics driven by current-induced spin–orbit torque. Recent observations of the sign flip of Hall conductivity imply that the spin–orbit torque is strong enough to flip magnetization within this heterostructure. Motivated by this, our study elucidates the conditions governing spin flips by studying the magnetization dynamics. We establish that the interplay between spin-anisotropy and spin–orbit torque plays a crucial role in the magnetization dynamics. Furthermore, we categorize various modes of magnetization dynamics, constructing a comprehensive phase diagram across distinct energy scales, damping constants, and applied frequencies. We also consider the effect of a magnetic field on the magnetization dynamics. This research not only offers insights into controlling spin direction but also charts a new pathway to the practical application of spin–orbit coupled systems.","PeriodicalId":501713,"journal":{"name":"npj Spintronics","volume":" ","pages":"1-10"},"PeriodicalIF":0.0,"publicationDate":"2024-08-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s44306-024-00045-0.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141968511","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-08-02DOI: 10.1038/s44306-024-00049-w
Amal Aldarawsheh, Moritz Sallermann, Muayad Abusaa, Samir Lounis
Antiferromagnetic (AFM) skyrmions have emerged as a highly promising avenue in the realm of spintronics, particularly for the development of advanced racetrack memory devices. A distinguishing feature of AFM skyrmions is the cancellation of their net topological charge, leading to an anticipated absence of the skyrmion Hall effect (SkHE). Here, we unveil that the latter is finite under the influence of spin-transfer torque, depending on the direction of the injected current impinging on intrinsic AFM skyrmions emerging in Cr/Pd/Fe trilayer on Ir(111) surface. Hinging on first principles combined with atomistic spin dynamics simulations, we identify the origin of the SkHE, which is due to the ellipticity of the skyrmions, and we uncover that FM skyrmions in the underlying Fe layer act as effective traps for AFM skyrmions, confining them and affecting their velocity. These findings hold significant promise for spintronic applications, the design of multi-purpose skyrmion tracks while advancing our understanding of AFM–FM skyrmion interactions and hybrid soliton dynamics in heterostructures.
{"title":"Current-driven dynamics of antiferromagnetic skyrmions: from skyrmion Hall effects to hybrid inter-skyrmion scattering","authors":"Amal Aldarawsheh, Moritz Sallermann, Muayad Abusaa, Samir Lounis","doi":"10.1038/s44306-024-00049-w","DOIUrl":"10.1038/s44306-024-00049-w","url":null,"abstract":"Antiferromagnetic (AFM) skyrmions have emerged as a highly promising avenue in the realm of spintronics, particularly for the development of advanced racetrack memory devices. A distinguishing feature of AFM skyrmions is the cancellation of their net topological charge, leading to an anticipated absence of the skyrmion Hall effect (SkHE). Here, we unveil that the latter is finite under the influence of spin-transfer torque, depending on the direction of the injected current impinging on intrinsic AFM skyrmions emerging in Cr/Pd/Fe trilayer on Ir(111) surface. Hinging on first principles combined with atomistic spin dynamics simulations, we identify the origin of the SkHE, which is due to the ellipticity of the skyrmions, and we uncover that FM skyrmions in the underlying Fe layer act as effective traps for AFM skyrmions, confining them and affecting their velocity. These findings hold significant promise for spintronic applications, the design of multi-purpose skyrmion tracks while advancing our understanding of AFM–FM skyrmion interactions and hybrid soliton dynamics in heterostructures.","PeriodicalId":501713,"journal":{"name":"npj Spintronics","volume":" ","pages":"1-9"},"PeriodicalIF":0.0,"publicationDate":"2024-08-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s44306-024-00049-w.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141968510","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-08-02DOI: 10.1038/s44306-024-00048-x
Suhyeok An, Hyeong-Joo Seo, Dongryul Kim, Ki-Seung Lee, Eunchong Baek, Jun-Su Kim, Soobeom Lee, Chun-Yeol You
To reveal the role of chirality on field-free spin–orbit torque (SOT) induced magnetization switching, we propose an existence of z-torque through the formation of noncollinear spin texture during SOT-induced magnetization switching in a laterally two-level perpendicular magnetic anisotropy (PMA) system. For the investigation of torque, we simulate magnetization dynamics in the two-level PMA system with SOT, which generates the noncollinear spin texture. From the spatial distribution of magnetic energy, we reveal the additional z-directional torque contribution in the noncollinear spin texture, which is unexpected in the conventional SOT-induced magnetization switching in collinear spin texture. The z-directional torque originates from the interaction between the chirality of the noncollinear spin texture and the interfacial Dzyaloshinskii-Moriya interaction of the system. Furthermore, the experimental observation of the asymmetric magnetization switching to the direction of the current flow in the two-level PMA system supports our theoretical expectation.
为了揭示手性对无场自旋轨道力矩（SOT）诱导的磁化切换的作用，我们提出了在横向两级垂直磁各向异性（PMA）系统中，通过在 SOT 诱导的磁化切换过程中形成非共线性自旋纹理而存在 z 扭矩。为了研究转矩，我们模拟了带有 SOT 的两级 PMA 系统中的磁化动态，SOT 会产生非线性自旋纹理。通过磁能的空间分布，我们揭示了非共线性自旋纹理中额外的 z 方向转矩贡献，这在传统的 SOT 诱导的共线性自旋纹理磁化切换中是意想不到的。z方向转矩源于非共线性自旋纹理的手性与系统的界面Dzyaloshinskii-Moriya相互作用。此外，在两级 PMA 系统中观察到的非对称磁化向电流方向切换的实验结果也支持了我们的理论预期。
{"title":"Noncollinear spin texture-driven torque in deterministic spin–orbit torque-induced magnetization switching","authors":"Suhyeok An, Hyeong-Joo Seo, Dongryul Kim, Ki-Seung Lee, Eunchong Baek, Jun-Su Kim, Soobeom Lee, Chun-Yeol You","doi":"10.1038/s44306-024-00048-x","DOIUrl":"10.1038/s44306-024-00048-x","url":null,"abstract":"To reveal the role of chirality on field-free spin–orbit torque (SOT) induced magnetization switching, we propose an existence of z-torque through the formation of noncollinear spin texture during SOT-induced magnetization switching in a laterally two-level perpendicular magnetic anisotropy (PMA) system. For the investigation of torque, we simulate magnetization dynamics in the two-level PMA system with SOT, which generates the noncollinear spin texture. From the spatial distribution of magnetic energy, we reveal the additional z-directional torque contribution in the noncollinear spin texture, which is unexpected in the conventional SOT-induced magnetization switching in collinear spin texture. The z-directional torque originates from the interaction between the chirality of the noncollinear spin texture and the interfacial Dzyaloshinskii-Moriya interaction of the system. Furthermore, the experimental observation of the asymmetric magnetization switching to the direction of the current flow in the two-level PMA system supports our theoretical expectation.","PeriodicalId":501713,"journal":{"name":"npj Spintronics","volume":" ","pages":"1-8"},"PeriodicalIF":0.0,"publicationDate":"2024-08-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s44306-024-00048-x.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141968512","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-07-25DOI: 10.1038/s44306-024-00027-2
J. Godinho, P. K. Rout, R. Salikhov, O. Hellwig, Z. Šobáň, R. M. Otxoa, K. Olejník, T. Jungwirth, J. Wunderlich
Antiferromagnetic materials have unique properties due to their alternating spin arrangements. Their compensated magnetic order, robust against external magnetic fields, prevents long-distance crosstalk from stray fields. Furthermore, antiferromagnets with combined parity and time-reversal symmetry enable electrical control and detection of ultrafast exchange-field enhanced spin manipulation up to THz frequencies. Here we report the experimental realization of a nonvolatile antiferromagnetic memory mimicking an artificial synapse, in which the reconfigurable synaptic weight is encoded in the ratio between reversed antiferromagnetic domains. The non-volatile memory is “written” by spin-orbit torque-driven antiferromagnetic domain wall motion and “read” by nonlinear magnetotransport. We show that the absence of long-range interacting stray magnetic fields leads to very reproducible electrical pulse-driven variations of the synaptic weights.
{"title":"Antiferromagnetic domain wall memory with neuromorphic functionality","authors":"J. Godinho, P. K. Rout, R. Salikhov, O. Hellwig, Z. Šobáň, R. M. Otxoa, K. Olejník, T. Jungwirth, J. Wunderlich","doi":"10.1038/s44306-024-00027-2","DOIUrl":"10.1038/s44306-024-00027-2","url":null,"abstract":"Antiferromagnetic materials have unique properties due to their alternating spin arrangements. Their compensated magnetic order, robust against external magnetic fields, prevents long-distance crosstalk from stray fields. Furthermore, antiferromagnets with combined parity and time-reversal symmetry enable electrical control and detection of ultrafast exchange-field enhanced spin manipulation up to THz frequencies. Here we report the experimental realization of a nonvolatile antiferromagnetic memory mimicking an artificial synapse, in which the reconfigurable synaptic weight is encoded in the ratio between reversed antiferromagnetic domains. The non-volatile memory is “written” by spin-orbit torque-driven antiferromagnetic domain wall motion and “read” by nonlinear magnetotransport. We show that the absence of long-range interacting stray magnetic fields leads to very reproducible electrical pulse-driven variations of the synaptic weights.","PeriodicalId":501713,"journal":{"name":"npj Spintronics","volume":" ","pages":"1-8"},"PeriodicalIF":0.0,"publicationDate":"2024-07-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s44306-024-00027-2.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141806195","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-07-25DOI: 10.1038/s44306-024-00043-2
Jesus C. Toscano-Figueroa, Daniel Burrow, Victor H. Guarochico-Moreira, Chengkun Xie, Thomas Thomson, Irina V. Grigorieva, Ivan J. Vera-Marun
We exploit the geometry of magnetic nanowires, which define 1D contacts to an encapsulated graphene channel, to introduce an out-of-plane component in the polarisation of spin carriers. By design, the magnetic nanowires traverse the angled sides of the 2D material heterostructure. Consequently, the easy axis of the nanowires is inclined, and so the local magnetisation is oblique at the injection point. As a result, when performing non-local spin valve measurements we simultaneously observe both switching and spin precession phenomena, implying the spin population possesses both in-plane and out-of-plane polarisation components. By comparing the relative magnitudes of these components, we quantify the angle of the total spin polarisation vector. The extracted angle is consistent with the angle of the nanowire at the graphene interface, evidencing that the effect is a consequence of the device geometry. This simple method of spin-based vector magnetometry provides an alternative technique to define the spin polarisation in 2D spintronic devices.
{"title":"Oblique spin injection to graphene via geometry controlled magnetic nanowires","authors":"Jesus C. Toscano-Figueroa, Daniel Burrow, Victor H. Guarochico-Moreira, Chengkun Xie, Thomas Thomson, Irina V. Grigorieva, Ivan J. Vera-Marun","doi":"10.1038/s44306-024-00043-2","DOIUrl":"10.1038/s44306-024-00043-2","url":null,"abstract":"We exploit the geometry of magnetic nanowires, which define 1D contacts to an encapsulated graphene channel, to introduce an out-of-plane component in the polarisation of spin carriers. By design, the magnetic nanowires traverse the angled sides of the 2D material heterostructure. Consequently, the easy axis of the nanowires is inclined, and so the local magnetisation is oblique at the injection point. As a result, when performing non-local spin valve measurements we simultaneously observe both switching and spin precession phenomena, implying the spin population possesses both in-plane and out-of-plane polarisation components. By comparing the relative magnitudes of these components, we quantify the angle of the total spin polarisation vector. The extracted angle is consistent with the angle of the nanowire at the graphene interface, evidencing that the effect is a consequence of the device geometry. This simple method of spin-based vector magnetometry provides an alternative technique to define the spin polarisation in 2D spintronic devices.","PeriodicalId":501713,"journal":{"name":"npj Spintronics","volume":" ","pages":"1-6"},"PeriodicalIF":0.0,"publicationDate":"2024-07-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s44306-024-00043-2.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141968507","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Strong correlation, breaking symmetry, band topology, collective excitation, and quantum confinement represent important features of quantum materials. When quantum materials intersect with spintronics, these key features fundamentally enhance the performance of spin-dependent phenomena. In this review, we examine recent advancements in the material requirements for spintronics and investigate the role of quantum effects in enhancing the functionalization of these devices. Current-induced spin-orbit torques offer a versatile tool to manipulate and excite magnetic order, with decoupled read and write paths that excite various types of materials. One crucial aspect of a spintronic device is the transition of writing layers from traditional transport to quantum transport. The recording layer, on the other hand, employs two-dimensional magnetic materials to achieve the ultimate limit of single-layer magnetic storage. Additionally, the utilization of antiferromagnetic and altermagnetic materials makes them suitable for high-density memories with minimal inter-bit dipole interactions and fast writing speed. Exploiting these emerging quantum materials, in spintronic devices and exploring how quantum effects enhance device functionality show significant potential for spintronic applications in the future.
{"title":"Quantum materials for spintronic applications","authors":"Yaqin Guo, Xu Zhang, Zhi Huang, Jinyan Chen, Zijun Luo, Jing Zhang, Jingfeng Li, Zhaowei Zhang, Jinkui Zhao, Xiufeng Han, Hao Wu","doi":"10.1038/s44306-024-00038-z","DOIUrl":"10.1038/s44306-024-00038-z","url":null,"abstract":"Strong correlation, breaking symmetry, band topology, collective excitation, and quantum confinement represent important features of quantum materials. When quantum materials intersect with spintronics, these key features fundamentally enhance the performance of spin-dependent phenomena. In this review, we examine recent advancements in the material requirements for spintronics and investigate the role of quantum effects in enhancing the functionalization of these devices. Current-induced spin-orbit torques offer a versatile tool to manipulate and excite magnetic order, with decoupled read and write paths that excite various types of materials. One crucial aspect of a spintronic device is the transition of writing layers from traditional transport to quantum transport. The recording layer, on the other hand, employs two-dimensional magnetic materials to achieve the ultimate limit of single-layer magnetic storage. Additionally, the utilization of antiferromagnetic and altermagnetic materials makes them suitable for high-density memories with minimal inter-bit dipole interactions and fast writing speed. Exploiting these emerging quantum materials, in spintronic devices and exploring how quantum effects enhance device functionality show significant potential for spintronic applications in the future.","PeriodicalId":501713,"journal":{"name":"npj Spintronics","volume":" ","pages":"1-11"},"PeriodicalIF":0.0,"publicationDate":"2024-07-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s44306-024-00038-z.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141968509","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-07-25DOI: 10.1038/s44306-024-00042-3
O. Gomonay, V. P. Kravchuk, R. Jaeschke-Ubiergo, K. V. Yershov, T. Jungwirth, L. Šmejkal, J. van den Brink, J. Sinova
We present a phenomenological theory of altermagnets, that captures their unique magnetization dynamics and allows modeling magnetic textures in this new magnetic phase. Focusing on the prototypical d-wave altermagnets, e.g., RuO2, we can explain intuitively the characteristic lifted degeneracy of their magnon spectra, by the emergence of an effective sublattice-dependent anisotropic spin stiffness arising naturally from the phenomenological theory. We show that as a consequence the altermagnetic domain walls, in contrast to antiferromagnets, have a finite gradient of the magnetization, with its strength and gradient direction connected to the altermagnetic anisotropy, even for 180° domain walls. This gradient generates a ponderomotive force in the domain wall in the presence of a strongly inhomogeneous external magnetic field, which may be achieved through magnetic force microscopy techniques. The motion of these altermagentic domain walls is also characterized by an anisotropic Walker breakdown, with much higher speed limits of propagation than ferromagnets but lower than antiferromagnets.
我们提出了一种关于变磁体的现象学理论，它捕捉到了变磁体独特的磁化动态，并能对这种新磁相的磁纹理进行建模。通过现象学理论中自然产生的依赖于亚晶格的有效各向异性自旋刚度的出现，我们可以直观地解释典型的 d 波变磁体（如 RuO2）磁子谱的提升变性特征。我们的研究表明，与反铁磁体相反，改磁畴壁具有有限的磁化梯度，其强度和梯度方向与改磁各向异性相关，即使是 180° 的畴壁也是如此。在强不均匀外磁场的作用下，这种梯度会在畴壁中产生思动力，这可以通过磁力显微镜技术来实现。这些变磁性畴壁的运动特征也是各向异性的沃克击穿，其传播速度极限远高于铁磁体，但低于反铁磁体。
{"title":"Structure, control, and dynamics of altermagnetic textures","authors":"O. Gomonay, V. P. Kravchuk, R. Jaeschke-Ubiergo, K. V. Yershov, T. Jungwirth, L. Šmejkal, J. van den Brink, J. Sinova","doi":"10.1038/s44306-024-00042-3","DOIUrl":"10.1038/s44306-024-00042-3","url":null,"abstract":"We present a phenomenological theory of altermagnets, that captures their unique magnetization dynamics and allows modeling magnetic textures in this new magnetic phase. Focusing on the prototypical d-wave altermagnets, e.g., RuO2, we can explain intuitively the characteristic lifted degeneracy of their magnon spectra, by the emergence of an effective sublattice-dependent anisotropic spin stiffness arising naturally from the phenomenological theory. We show that as a consequence the altermagnetic domain walls, in contrast to antiferromagnets, have a finite gradient of the magnetization, with its strength and gradient direction connected to the altermagnetic anisotropy, even for 180° domain walls. This gradient generates a ponderomotive force in the domain wall in the presence of a strongly inhomogeneous external magnetic field, which may be achieved through magnetic force microscopy techniques. The motion of these altermagentic domain walls is also characterized by an anisotropic Walker breakdown, with much higher speed limits of propagation than ferromagnets but lower than antiferromagnets.","PeriodicalId":501713,"journal":{"name":"npj Spintronics","volume":" ","pages":"1-8"},"PeriodicalIF":0.0,"publicationDate":"2024-07-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s44306-024-00042-3.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141968508","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-07-25DOI: 10.1038/s44306-024-00040-5
Taewoo Ha, Kyung Ik Sim, Howon Lee, Hyun Jun Shin, Sanghoon Kim, Se Kwon Kim, Jae Hoon Kim, Dong-Soo Han, Young Jai Choi, Byung Cheol Park
Magnonics, a crucial domain in information science and technology, utilizes spin waves in magnets as efficient information carriers. While antiferromagnets have been suggested for versatile magnonic platform because of the coexistence of right- and left-handed spin waves, their energetic degeneracy poses challenges for observation through spectral measurements, limiting their applicability. Recent observations of distinct spin wave handedness within the gigahertz regime have reported but, are yet to be demonstrated in terahertz (THz) frequencies of antiferromagnetic spin waves. Most of all, the coherence of spin waves is a key aspect of quantum information. Here, employing THz time-domain spectroscopy—a direct, precise, and easy probe for monitoring coherent spin wave dynamics—we discern chiral antiferromagnetic spin waves of opposite phase windings in the time domain, noting their handedness reversal across the angular momentum compensation temperature in ferrimagnets. We establish a principle for directly measuring the handedness of coherent antiferromagnetic spin waves in ferrimagnets with net magnetic moment M ≠ 0 but angular momentum L = 0. Our multidimensional access in the time and spectral domain enables the accurate determination of critical temperature and the dynamic observation of coherent chiral spin waves simultaneously in a single experiment, with potential applications in exploring other quantum chiral entities.
磁学是信息科学与技术的一个重要领域，它利用磁体中的自旋波作为高效的信息载体。虽然反铁磁体因左右手自旋波的共存而被认为是多功能的磁性平台，但其能量退化性给光谱测量观测带来了挑战，限制了其适用性。最近有报道称在千兆赫范围内观测到了不同的自旋波手性，但在太赫兹（THz）频率的反铁磁性自旋波中尚未得到证实。最重要的是，自旋波的相干性是量子信息的一个关键方面。在这里，我们利用太赫兹时域光谱--一种直接、精确、易于监测相干自旋波动态的探针--在时域中发现了相位绕组相反的手性反铁磁自旋波，并注意到它们在铁磁体角动量补偿温度下的手性反转。我们建立了一种原理，可以直接测量净磁矩 M≠0 但角动量 L = 0 的铁氧体中相干反铁磁自旋波的手性。我们在时域和频谱域的多维访问使我们能够在一次实验中同时精确测定临界温度和动态观测相干手性自旋波，这在探索其他量子手性实体方面具有潜在的应用价值。
{"title":"Real-time observation of coherent spin wave handedness","authors":"Taewoo Ha, Kyung Ik Sim, Howon Lee, Hyun Jun Shin, Sanghoon Kim, Se Kwon Kim, Jae Hoon Kim, Dong-Soo Han, Young Jai Choi, Byung Cheol Park","doi":"10.1038/s44306-024-00040-5","DOIUrl":"10.1038/s44306-024-00040-5","url":null,"abstract":"Magnonics, a crucial domain in information science and technology, utilizes spin waves in magnets as efficient information carriers. While antiferromagnets have been suggested for versatile magnonic platform because of the coexistence of right- and left-handed spin waves, their energetic degeneracy poses challenges for observation through spectral measurements, limiting their applicability. Recent observations of distinct spin wave handedness within the gigahertz regime have reported but, are yet to be demonstrated in terahertz (THz) frequencies of antiferromagnetic spin waves. Most of all, the coherence of spin waves is a key aspect of quantum information. Here, employing THz time-domain spectroscopy—a direct, precise, and easy probe for monitoring coherent spin wave dynamics—we discern chiral antiferromagnetic spin waves of opposite phase windings in the time domain, noting their handedness reversal across the angular momentum compensation temperature in ferrimagnets. We establish a principle for directly measuring the handedness of coherent antiferromagnetic spin waves in ferrimagnets with net magnetic moment M ≠ 0 but angular momentum L = 0. Our multidimensional access in the time and spectral domain enables the accurate determination of critical temperature and the dynamic observation of coherent chiral spin waves simultaneously in a single experiment, with potential applications in exploring other quantum chiral entities.","PeriodicalId":501713,"journal":{"name":"npj Spintronics","volume":" ","pages":"1-8"},"PeriodicalIF":0.0,"publicationDate":"2024-07-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s44306-024-00040-5.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141804434","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-07-17DOI: 10.1038/s44306-024-00041-4
Insu Baek, Seungyun Han, Suik Cheon, Hyun-Woo Lee
Nonlinear spintronics combines nonlinear dynamics with spintronics, opening up new possibilities beyond linear responses. A recent theoretical work [Xiao et al. Phys. Rev. Lett. 130, 166302 (2023)] predicts the nonlinear generation of spin density [nonlinear spin Edelstein effect (NSEE)] in centrosymmetric metals based on symmetry analysis combined with first-principle calculation. This paper focuses on the fundamental role of orbital degrees of freedom for the nonlinear generation in centrosymmetric systems. Using a combination of tight-binding model and density functional theory calculations, we demonstrate that nonlinear orbital density can arise independently of spin–orbit coupling. In contrast, spin density follows through spin–orbit coupling. We further elucidate the microscopic mechanism responsible for this phenomenon, which involves the NSEE induced by electric-field-induced orbital Rashba texture. In addition, we also explore the potential applications of the nonlinear orbital and spin Edelstein effect for magnetic-field-free switching of magnetization.
非线性自旋电子学将非线性动力学与自旋电子学相结合，开辟了超越线性响应的新可能性。最近的一项理论工作[肖等人，Phys. Rev. Lett. 130, 166302 (2023)]基于对称性分析结合第一性原理计算，预测了中心对称金属中自旋密度的非线性产生[非线性自旋爱德斯坦效应（NSEE）]。本文重点研究了轨道自由度对中心对称体系中非线性产生的基本作用。通过结合紧密结合模型和密度泛函理论计算，我们证明了非线性轨道密度可以独立于自旋轨道耦合而产生。相反，自旋密度是通过自旋轨道耦合产生的。我们进一步阐明了造成这一现象的微观机制，其中涉及由电场诱导的轨道拉什巴纹理引起的非线性自旋密度。此外，我们还探讨了非线性轨道和自旋爱德斯坦效应在无磁场磁化切换中的潜在应用。
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Pub Date : 2024-07-17DOI: 10.1038/s44306-024-00039-y
Xin Li, Hanuman Singh, Jie Lin, Shuai Zhang, Bao Yi, Jyotirmoy Chatterjee, Zhuyun Xiao, Sucheta Mondal, Nobumichi Tamura, Rob N. Candler, Long You, Jeffrey Bokor, Jeongmin Hong
Recent advancements in electrically controlled spin devices have been made possible through the use of multiferroic systems comprising ferroelectric (FE) and ferromagnetic (FM) materials. This progress provides a promising avenue for developing energy-efficient devices that allow for electrically controlled magnetization switching. In this study, we fabricated spin orbit torque (SOT) devices using multiferroic composites and examined the angular dependence of SOT effects on localized in-plane strain induced by an out-of-plane electric field applied to the piezoelectric substrate. The induced strain precisely modulates magnetization switching via the SOT effect in multiferroic heterostructures, which also exhibit remarkable capability to modulate strain along different orientations – a feature with great potential for future applications in logic device arrays. To investigate the influence of electric fields on magnetization switching, harmonic Hall measurements, synchrotron-powered x-ray magnetic circular dichroism-photoemission electron microscopy (XMCD-PEEM), x-ray diffraction (XRD), magnetic force microscopy (MFM), and micromagnetic simulation were conducted. The results demonstrate that electric-field-induced strain enables precise control of SOT-induced magnetization switching with significantly reduced energy consumption, making it highly suitable for next-generation spin logic devices.
通过使用由铁电（FE）和铁磁（FM）材料组成的多铁性系统，电控自旋设备取得了最新进展。这一进展为开发可实现电控磁化切换的高能效器件提供了一条大有可为的途径。在这项研究中，我们利用多铁性复合材料制造了自旋轨道转矩（SOT）器件，并研究了自旋轨道转矩效应对施加到压电基板上的面外电场诱导的局部面内应变的角度依赖性。诱导应变通过多铁氧体异质结构中的 SOT 效应精确调节磁化开关，这种异质结构还具有沿不同方向调节应变的显著能力--这一特性在逻辑器件阵列中的未来应用中具有巨大潜力。为了研究电场对磁化切换的影响，研究人员进行了谐波霍尔测量、同步加速器驱动的 X 射线磁性圆二色性-光电发射电子显微镜 (XMCD-PEEM)、X 射线衍射 (XRD)、磁力显微镜 (MFM) 和微磁模拟。结果表明，电场诱导应变能够精确控制 SOT 诱导的磁化开关，并显著降低能耗，因此非常适合用于下一代自旋逻辑器件。
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