Terahertz magnon spintronics with non-collinear antiferromagnets

Dhanvir Singh Rana

Department of Physics, Indian Institute of Science Education and Research (IISER) Bhopal, India

The terahertz (THz) spectrum (0.1-10 THz) offers promising opportunities in the development of next-generation data processing and quantum memory technologies. These aspirations are driven by simultaneous developments in the THz spectrum and the area of spintronics, magnonics, caloritronic, and many more [1]. In magnetic systems, magnons – the quanta of spin waves-in a spin-ordered state envisage the prospects of non-Boolean-based spin wave computation, magnon logic gates, and so on [1]. However, magnonics has been widely explored in ferromagnets resulting in gigahertz magnons. However, the area of magnonic can be extended to ultra-low dissipation and ultrafast THz region as the antiferromagnets have magnons in this region. This offers THz radiation-based tools play a prominent role in exploring the technological utility of antiferromagnets which, so far, have played only a passive role in the emergence of magnetic devices. The THz radiation mainly couples with the magnetic-dipole moment of the spins unveiling not only the low-energy antiferromagnetic magnons but also its interplay with distinct quasiparticles such as phonons, photons, polaritons, and many more. Recently, for the first time, magnons sum and difference generation was demonstrated in YFeO3, thus, raising the importance of algebraic operations of different THz frequency magnons [2, 3]. This study necessitates the exploration of antiferromagnets possessing closely spaced magnons in terahertz region (0.1-2 THz) for their potential in THz magnon algebraic logic operations [3]. Such control over spin-waves/magnon can be contemplated in magnetoelectric/multiferroic systems, in which the spin and electric orders are entangled, resulting in electric as well as magnetic control of magnons.

In this work, I’ll present our recent work in exploration of a variety of non-collinear magnets for magnon and magnon-phonon excitation modes in the THz spectral region, considering two examples. First, I will show that A₄B₂O₉ (A=Co and B=Nb, Ta) family of non-collinear magnetoelectric antiferromagnetic [4, 5] exhibit i) a multitude of low-energy antiferromagnetic resonances comprised of magnons, phonons, and hybridized spin-phonon coupled modes and ii) the notion of beyond conventional magnon, that is, electromagnon. The second example is based on RCrO₃ (R=rare-earth) orthochromates in which weak magnetic moment is accompanied by sub-THz magnon modes along with complex crystal-field excitations

References
[1] Leitenstorfer et al., “The 2023 terahertz science and technology roadmap,” J. Phys. D: Appl. Phys. (2023)
[2] Zhang et al., “Terahertz field-induced nonlinear coupling of two magnon modes in an antiferromagnet,” Nature Physics (2024)
[3] B. S. Mehra and D. S. Rana, “Terahertz magnon algebra,” Nature Physics (2024)
[4] R. Dagar, S. Yadav, M. Kinha, B.S. Mehra, R. Rawat, K. Singh, D. S. Rana, “Magnetic-field-controlled multitude of spin excitation modes in magnetoelectric Co4Nb2O9 as investigated by magneto-terahertz spectroscopy,” Phys. Rev. Material. (2022)
[5] B. S. Mehra, S. Kumar, G. Dubey, A. Shyam, A. Kumar, K Anirudh, K. Singh, D. S. Rana (unpublished)