The planar Hall effect (PHE), wherein a rotating magnetic field in the plane of a sample induces oscillating transverse voltage, has recently garnered attention in a wide range of topological metals and insulators. The observed twofold oscillations in ρyx as the magnetic field completes one rotation are the result of chiral, orbital, and/or spin effects. The antiperovskites A3BO (A=Ca, Sr, Ba; B=Sn, Pb) are topological crystalline insulators whose low-energy excitations are described by a generalized Dirac equation for fermions with total angular momentum J=32. We report unusual sixfold oscillations in the PHE of Sr3SnO, which persisted nearly up to room temperature. Multiple harmonics (twofold, fourfold, and sixfold), which exhibited distinct field and temperature dependencies, were detected in ρxx and ρyx. These observations are more diverse than those in other Dirac and Weyl semimetals and point to a richer interplay of microscopic processes underlying the PHE in the antiperovskites.Received 10 November 2020Accepted 4 March 2021DOI:https://doi.org/10.1103/PhysRevResearch.3.013268Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Open access publication funded by the Max Planck Society.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasHall effectMagnetotransportTopological materialsCondensed Matter, Materials & Applied Physics