Epitaxial columnar growth of strain-free antiferromagnetic Weyl semimetal Mn <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si104.svg" display="inline" id="d1e765"> <mml:msub> <mml:mrow/> <mml:mrow> <mml:mn>3</mml:mn> </mml:mrow> </

Weyl semimetal thin films with excellent crystalline quality are of great interest for antiferromagnetic spintronics. Mn 3 Sn is one Weyl semimetal with great properties and promise for exciting science and applications. It has proven very challenging, however, to grow Mn 3 Sn thin films with smooth surfaces, negligible strain, and excellent crystallinity. In this work, we discuss the successful preparation of epitaxial Mn 3 Sn (0001)-oriented thin films via molecular beam epitaxial growth on c -plane wurtzite GaN which was grown by MBE on Al 2 O 3 (0001). We present the reflection high energy electron diffraction analysis along with x-ray diffraction in order to demonstrate the crystalline quality of the film, and we give atomic models to explain the epitaxial orientation relationships between the crystal lattices of the substrate, GaN layer, and Mn 3 Sn layer. Importantly, we discuss the film lattice parameters as compared to expected values, demonstrating negligible strain both in-plane and out-of-plane . Atomic force microscopy reveals an epitaxial columnar growth mode characterized by flat-top-mesa islands, while scanning tunneling microscopy shows the atomically smooth surfaces of the mesa-top structures. Finally, Rutherford backscattering informs the stoichiometry of the film as well as the layer thicknesses. • Al 2 O 3 (0001) converts to AlN-like surface with plasma nitridation. • Mn 3 Sn grows with streaky RHEED pattern on wurtzite c -plane GaN. • In-plane lattice parameter ( a ) for Mn 3 Sn thin film has ≤ 0.018% strain. • Out-of-plane lattice parameter ( c ) for Mn 3 Sn thin film has ≤ 0.044% strain. • Mn 3 Sn layer consists of atomically smooth mesa-topped columnar islands.