Coherent spin-wave transport in an antiferromagnet

Abstract

Magnonics is a research field complementary to spintronics, in which the quanta of spin waves (magnons) replace electrons as information carriers, promising less energy dissipation 1-3 . The development of ultrafast nanoscale magnonic logic circuits calls for new tools and materials to generate coherent spin waves with frequencies as high, and wavelengths as short, as possible 4,5 . Antiferromagnets can host spin waves at THz frequencies and are therefore seen as a future platform for the fastest and the least dissipative transfer of information 6-11 . However, the generation of short-wavelength coherent propagating magnons in antiferromagnets has so far remained elusive. Here we report the efficient emission and detection of a nanometer-scale wavepacket of coherent propagating magnons in antiferromagnetic DyFeO3 using ultrashort pulses of light. The subwavelength confinement of the laser field due to large absorption creates a strongly nonuniform spin excitation profile, enabling the propagation of a broadband continuum of coherent THz spin waves. The wavepacket features magnons with detected wavelengths down to 125 nm that propagate with supersonic velocities of more than 13 km/s into the material. The long-sought source of coherent shortwavelength spin carriers demonstrated here opens up new prospects for THz antiferromagnetic magnonics and coherence-mediated logic devices at THz frequencies.Antiferromagnetic insulators (AFMs) are prime candidates to replace ferromagnets (FMs) as active media in the quest towards high-speed spin transport and large spectral bandwidth operation [6][7][8] . Integration of AFMs in future wave-based technologies 3 crucially requires the realization of coherent (ballistic) transport of antiferromagnetic spin waves over large distances 5 . In this regard, non-uniform spin-wave modes with short wavelengths (λ ≲ 100 nm) are of particular importance: they can operate at THz clock rates, exhibit high propagation velocities and enable the miniaturization of devices down to the nanoscale. Phase-coherent ballistic spin transport in AFMs

Orthogonal interlayer coupling in an all-antiferromagnetic junction

“…It should be clari ed that the second peak can exist when the coupling energy is large enough to overcome the Zeeman energy of the top Fe 2 O 3 at the valley (ii), otherwise the n (top Fe 2 O 3 ) will maintain spin-op state rather than deviating towards n // H. The magnitude of the second peak is smaller than the rst one can be ascribed to less component of n along x-axis. In contrast, the SMR in inverted sandwich, Fe 2 O 3 (4)/Cr 2 O 3 (4.4)/Fe 2 O 3 (12) (Supplementary Note 7), does not present resistance peak signal before H = 0, demonstrating that the n in the 12 nm-thick Fe 2 O 3 maintains spin-op state rather than deviating towards H at low magnetic eld because of the large Zeeman energy, indicating the existence of the orthogonal coupling.…”

“…We rst show in Fig. 2a SMR signals of a control sample Fe 2 O 3 (12)/Pt(4) (units in nanometers), where the magnetic eld (H) and current (I) is along x-axis and the spin polarization generated by the spin Hall effect of Pt is along y-axis. As expected, comparatively low resistance states at high magnetic elds re ect that the Néel vector (n) of Fe 2 O 3 is perpendicular to H (I) due to the spin-op at high elds and deviates towards H (I) at low elds, which is quite characteristic for negative SMR of AFM [17][18][19][20] .…”

“…Read Full License drawbacks such as large stray eld which is destructive for the tightly packed devices, and the intrinsic gigahertz frequency which limits the fundamental operating speed of FM system. Antiferromagnets (AFMs) are promising candidates for solving these problems and for the next generation of spintronics because of the subtle net moment which eliminates operation cross-talk 7,8 , and extremely high eigenfrequency up to terahertz [9][10][11][12] . The interlayer coupling of AFMs has been overlooked because the collinear parallel and antiparallel arrangements are indiscernible and useless for application, since most antiferromagnets could be seen as having symmetry macroscopically at zero eld.…”

Multi-Center Magnon Excitations Open the Entire Brillouin Zone to Terahertz Magnetometry of Quantum Magnets

“…Attempts to overcome this constraint are subject of current research and first promising results have been reported. [9][10][11] In THz spectroscopy, with the aid of ultrafast lasers and advanced detection schemes, dynamical processes in the (sub-) picosecond range become accessible. [12,13] This progress allows not only performing time-resolved studies but enables a control of magnetization dynamics.…”

“…[17,18] Other examples include the coherent generation of magnons. [11] Control over THz-driven spin precession [19][20][21][22] opens the field of THz magnetometry, i.e. the fully optical extraction of magnetic properties.…”