Microscopic evidence of a quantum magnetization process in the S=12 triangular-lattice Heisenberg-like antiferromagnet Ba3CoSb2O9

We report results of the neutron scattering investigations of frustrated quantum magnet ${\mathrm{Ba}}₃{\mathrm{CoSb}}₂{\mathrm{O}}₉$ in magnetic fields up to 25.9 T. Contrary to other materials, ${\mathrm{Ba}}₃{\mathrm{CoSb}}₂{\mathrm{O}}₉$ exhibits properties typical of an ideal $S=\frac{1}{2}$ triangular lattice Heisenberg antiferromagnet, making it a perfect model system for testing theoretical predictions. In this work, we looked into the magnetization process in ${\mathrm{Ba}}₃{\mathrm{CoSb}}₂{\mathrm{O}}₉$ on a microscopic scale with a magnetic field applied in plane. A sequence of magnetic phase transitions, including the new high-field phase at 22.5 T reported recently has been followed at low temperatures as a function of field and modeled using the large-size cluster mean-field plus scaling method. Showing good agreement with the model, our results bridge the theory and the experiment providing microscopic information about the high-field spin ordering in $S=\frac{1}{2}$ triangular lattice Heisenberg-like antiferromagnet ${\mathrm{Ba}}₃{\mathrm{CoSb}}₂{\mathrm{O}}₉$.