Probing orbital magnetism of a kagome metal CsV₃Sb₅ by a tuning fork resonator

The recently discovered kagome metal CsV₃Sb₅ exhibits a complex phase diagram that encompasses frustrated magnetism, topological charge density wave (CDW), and superconductivity. One CDW state that breaks time-reversal symmetry was proposed in this compound, while the exact nature of the putative magnetic state remains elusive. To examine the thermodynamic state of CsV₃Sb₅ and assess the character of the associated magnetism, we conducted tuning fork resonator measurements of magnetotropic susceptibility over a broad range of angles, magnetic fields, and temperatures. We found a cascade of phase transitions in the CDW phase. Of particular interest is a highly anisotropic magnetic structure that arises below about 30 K, with a magnetic moment along the c-axis that has an extremely small magnitude. This magnetic state demonstrates extremely slow dynamics and small saturate field, all suggest that electronic phase below 30 K breaks time reversal symmetry and has an unconventional origin.