Periodic Reporting for period 4 - ASPIN (Antiferromagntic spintronics)
Periodo di rendicontazione: 2021-06-01 al 2022-09-30
Antiferromagnets and ferromagnets represent two fundamental forms of magnetism with antiferromagnets being the more abundant of the two. However, it has been notoriously difficult to manipulate and detect antiferromagnetic order by any practical means. The project builds on our recent discoveries of new relativistic phenomena that allow us to efficiently control and detect antiferromagnetic moments in spintronic devices and by this to unlock a multitude of known and newly identified unique features of this class of materials. We are exploring three intertwined research areas in order to scientifically establish the following: (i) The concept of antiferromagnetic memories suitable for the development of future “Beyond Moore” information technologies. (ii) The concept of antiferromagnetic spintronic components operating at timescales as short as picoseconds. (iii) The concept in which antiferromagnets provide a unifying platform for realizing synergies between spintronics and topological phenomena. The project opens and explores a new research avenue, with emerging and future information technologies at its horizon, where antiferromagnets take the center stage. The era of the International Technology Roadmap for Semiconductors is now officially at an end. The project will introduce to the public sector and industry an entirely new technology concept of microelectronics based on antiferromagnets. It is foreseen to have an impact on future IoT technologies by breaking present limits on energy efficiency, speed, integration, and security.
The research highlights achieved in the 3rd period of the project are as follows:
- we have successfully extended the range to ns-pulses
. we have extended the XMLD-PEEM imaging and demonstrated reversible and reproducible polarity-dependent non-volatile switching via 180◦ domain wall motion in CuMnAs
- we have extended the experiments by including concurrent table-top magneto-optical microscopy imaging and demonstrated stable and reversible current-induced switching of large-area (> 100μm2) antiferromagnetic NiO domains, disentangled magnetic and non-magnetic contributions to the electrical signal, and identified a complementary thermo-magneto-elastic switching mechanism
- we have extended this research front by showing a scalable and complete suppression by ultrafast optical gating of the terahertz-pulse induced switching of CuMnAs. Here the optical gating generates transiently conductive parallel channel in the semiconducting (GaAs or GaP) substrate underneath the metallic CuMnAs layer
- we have continued in this originally unanticipated but highly promising new research direction of ASPIN, focusing on the microscopic physics explanation of the new switching mechanism. We achieved atomic resolution by using differential phase contrast imaging within aberration-corrected scanning transmission electron microscopy (DPC-STEM). We have identified abrupt domain walls in the antiferromagnetic film corresponding to the N ́eel order reversal between two neighboring atomic planes. These atomic-scale domain walls have no precedence in traditional magnetism. The same applies to the earlier discovered characteristics of our devices hosting the nano-textures. All the key characteristics of the above electrical and optical switching can be attributed to these elementary atomic-scale textures. Consistent with this interpretation, we have also observed insensitivity of the electrical switching signals to magnetic fields as large as 60 T
- we have identified, again both theoretically and experimentally, another collinear anomalous Hall antiferromagnet Mn5Si3. Prompted by these results we have prepared a comprehensive review/outlook article on anomalous Hall antiferromagnets with a two-fold motivation: First, since Hall effects that are not governed by magnetic dipole symmetry breaking are at odds with the traditional understanding of the phenomenon, the topic deserves attention on its own. Second, the reincarnation within the broad antiferromagnetic family has placed the Hall effect in the middle of an emerging intriguing field of physics at the intersection of multipole magnetism, topological condensed matter, and spintronics. The discovery of the Hall effect in the compensated collinear magnets has also led us directly to a theory proposal that the essential non- relativistic reading and writing principles of ferromagnetic spintronics, namely the GMR/TMR and STT, should be readily available in this class of unconven- tional collinear antiferromagnets. This is an ample demonstration of the interlinked research under WP3 and WP1 in ASPIN. We have identified that the suitable compensated collinear magnets have a non-relativistic alternating spin-momentum locking. Finally, we have developed a non-relativistic spin-symmetry group formalism to systematically describe this unconventional class of antiferromagnets with the unprecedented topology of the non-relativistic band structure with the alternating spin-momentum locking. Based on the rigorous symmetry-group theory delimitation of this unconventional magnetic class, we have introduced a term ”altermagnets”.
- we have successfully extended the range to ns-pulses
. we have extended the XMLD-PEEM imaging and demonstrated reversible and reproducible polarity-dependent non-volatile switching via 180◦ domain wall motion in CuMnAs
- we have extended the experiments by including concurrent table-top magneto-optical microscopy imaging and demonstrated stable and reversible current-induced switching of large-area (> 100μm2) antiferromagnetic NiO domains, disentangled magnetic and non-magnetic contributions to the electrical signal, and identified a complementary thermo-magneto-elastic switching mechanism
- we have extended this research front by showing a scalable and complete suppression by ultrafast optical gating of the terahertz-pulse induced switching of CuMnAs. Here the optical gating generates transiently conductive parallel channel in the semiconducting (GaAs or GaP) substrate underneath the metallic CuMnAs layer
- we have continued in this originally unanticipated but highly promising new research direction of ASPIN, focusing on the microscopic physics explanation of the new switching mechanism. We achieved atomic resolution by using differential phase contrast imaging within aberration-corrected scanning transmission electron microscopy (DPC-STEM). We have identified abrupt domain walls in the antiferromagnetic film corresponding to the N ́eel order reversal between two neighboring atomic planes. These atomic-scale domain walls have no precedence in traditional magnetism. The same applies to the earlier discovered characteristics of our devices hosting the nano-textures. All the key characteristics of the above electrical and optical switching can be attributed to these elementary atomic-scale textures. Consistent with this interpretation, we have also observed insensitivity of the electrical switching signals to magnetic fields as large as 60 T
- we have identified, again both theoretically and experimentally, another collinear anomalous Hall antiferromagnet Mn5Si3. Prompted by these results we have prepared a comprehensive review/outlook article on anomalous Hall antiferromagnets with a two-fold motivation: First, since Hall effects that are not governed by magnetic dipole symmetry breaking are at odds with the traditional understanding of the phenomenon, the topic deserves attention on its own. Second, the reincarnation within the broad antiferromagnetic family has placed the Hall effect in the middle of an emerging intriguing field of physics at the intersection of multipole magnetism, topological condensed matter, and spintronics. The discovery of the Hall effect in the compensated collinear magnets has also led us directly to a theory proposal that the essential non- relativistic reading and writing principles of ferromagnetic spintronics, namely the GMR/TMR and STT, should be readily available in this class of unconven- tional collinear antiferromagnets. This is an ample demonstration of the interlinked research under WP3 and WP1 in ASPIN. We have identified that the suitable compensated collinear magnets have a non-relativistic alternating spin-momentum locking. Finally, we have developed a non-relativistic spin-symmetry group formalism to systematically describe this unconventional class of antiferromagnets with the unprecedented topology of the non-relativistic band structure with the alternating spin-momentum locking. Based on the rigorous symmetry-group theory delimitation of this unconventional magnetic class, we have introduced a term ”altermagnets”.
Spintronics is considered among the potential paradigm changing technologies for the "Beyond Moore" era. Present spintronic technologies rely on ferromagnets, however, ferromagnets possess innate limitations in packing density, magnetic-field hardness and utility in memristive-like (synapse-like) devices due to dipolar stray fields. Moreover, their operation speed is limited by the GHz ferromagnetic resonance scale.
Independently, the discovery of graphene and topological phenomena opened another prominent avenue of research in the “Beyond Moore” technology domain. In physics, While fascinating theoretically, practical means for controlling topologoical phases in devices have remained elusive. Spintronics could be a key here, however, ferromagnets again offer only a limited playground constrained by symmetry.
These limitations can be lifted by including antiferromagnets into spintronics as already demonstrated by our initial results. However, our understanding of basic principles that might allow in the future for turning our new antiferromagnetic spintronics concept into applications is still at its infancy. A continuing fundamental research program is necessary for fully unraveling the physical, material, and device aspects that govern the write/read speed and efficiency, and the retention characteristics of antiferromagnetic digital and analogue memory cells. Among others this will require improving our toolbox of techniques for imaging antiferromagnetic domain structures and dynamics with high spatial and temporal resolution. In the end, if successful, ASPIN will not merely enable a future digital or neuromorphic, and ultra-fast memory technology based on antiferromagnets. It will impact the entire research field of antiferromagnets whose utility has, so far, remained a virtually unwritten chapter in magnetism.
Independently, the discovery of graphene and topological phenomena opened another prominent avenue of research in the “Beyond Moore” technology domain. In physics, While fascinating theoretically, practical means for controlling topologoical phases in devices have remained elusive. Spintronics could be a key here, however, ferromagnets again offer only a limited playground constrained by symmetry.
These limitations can be lifted by including antiferromagnets into spintronics as already demonstrated by our initial results. However, our understanding of basic principles that might allow in the future for turning our new antiferromagnetic spintronics concept into applications is still at its infancy. A continuing fundamental research program is necessary for fully unraveling the physical, material, and device aspects that govern the write/read speed and efficiency, and the retention characteristics of antiferromagnetic digital and analogue memory cells. Among others this will require improving our toolbox of techniques for imaging antiferromagnetic domain structures and dynamics with high spatial and temporal resolution. In the end, if successful, ASPIN will not merely enable a future digital or neuromorphic, and ultra-fast memory technology based on antiferromagnets. It will impact the entire research field of antiferromagnets whose utility has, so far, remained a virtually unwritten chapter in magnetism.