A magnetic structure of ruthenium dioxide (RuO2) and altermagnetism

The magnetic structure of RuO2 and the Ru atomic configuration are unknown. A magnetic structure is inferred by confronting measured and calculated Bragg diffraction patterns and adjusting the latter to achieve satisfactory agreement. An accepted pattern, a magnetic symmetry, includes symmetry of sites occupied by the magnetic ions. As a realistic starting point, we provide diffraction patterns for a magnetic symmetry of RuO2, a descendent of the tetragonal parent structure, which accommodates a departure of Ru axial dipoles from the crystal c axis. A chiral signal and piezomagnetic effect are permitted, and a linear magnetoelectric effect forbidden. Features of the neutron diffraction pattern test the non-relativistic requirement of altermagnetism, and we scrutinize published room-temperature data. Specifically, one Bragg point is consistent with Ru orbital angular momentum and magnetic quadrupole both zero, and the latter result is not expected from non-relativistic altermagnetism. Azimuthal angle scans in resonant x-ray diffraction are sensitive to the Ru site symmetry and the atomic configuration. Acid tests of the studied magnetic symmetry include a chiral signature and null intensity for unrotated photon polarization.