Magnetic Structures at Fractional Magnetization Plateaus in a Shastry-Sutherland Quantum Magnet

In 2D magnetic compounds, the Shastry-Sutherland lattice (SSL) – a square lattice with antiferromagnetic exchange J between dimerized nearest neighbours and J’ between next-nearest-neighbours, has attracted attention due to its complex phase diagram, displaying a variety of novel phases as function of magnetic field. The 2D SSL model, consisting of an orthogonal dimer network of spin S=1/2 units, represents one of the very few topologies where the ground state of a geometrical frustrated lattice could be exactly solved. Previous experimental realizations of the SSL model such as SrCu2(BO3)2 (SCBO) exhibit multiple magnetization plateaus at fractional values, but the critical fields for SCBO are all above 27 T, too high for many experimental techniques. Lately, a new rare-earth SSL compound Er2Be2GeO7 (EBGO) with weaker interactions than SCBO was found to show magnetization plateaus with critical fields in a much more convenient range below 1T. We made an initial muSR study of EGBO on HiFi in March 2025, finding clear signatures of the transitions between magnetization plateaus. In addition to observing transitions between known plateaus at fractions ¼ and ½, an additional transition was revealed between the 0 and ¼ states. Alongside continuation muSR studies, this parallel single crystal diffraction study on WISH will be used to confirm this new phase and collect data also for the ¼ and ½ phases, allowing the details of the magnetic structure to be determined in each phase.