Ping Tang
Tohoku University, Japan

Abstract: Exchange Surface Spin Waves in Type-A van der Waals Antiferromagnets

Surface waves, the evanescent solutions of the wave equation at planar discontinuities, are of fundamental importance in surface physics, optics, phononics, electronics, and magnetism. Here we predict the emergence of surface spin-wave excitations within the bulk magnon band gap of type-A van der Waals antiferromagnets. In contrast to conventional magnetostatic Damon-Eshbach modes, they are pure exchange modes owing to reduced interlayer exchange coupling at the surface layers, and thus persist in ultrathin multilayer stacks and at large wave numbers. We show that they can be efficiently excited by electromagnetic waves, with absorption power comparable to or even exceeding that of bulk modes. Moreover, their emitted magnetic stray fields exhibit pronounced even-odd oscillations with the number of monolayers that should be observable by NV-center magnetometry [1].

Figure 1: Surface spin waves in perpendicularly magnetized A-type van der Waals antiferromagnets. (a), (b) For an even number of monolayers, two surface modes are localized at opposite surfaces with opposite chiralities. (c),(d) For an odd number of monolayers, there are two surface modes of the same (right-handed) chirality with in-phase (c) and out-of-phase (d) spin dynamics between the top and bottom surface amplitudes.

References:

[1] Z. Sun, F. Li, G. E. W. Bauer, and P. Tang*, arXiv:2504.21465

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Ping TangTohoku University, Japan

Ping Tang
Tohoku University, Japan