Metastable states in the frustrated triangular compounds Ca3Co2−xMnxO6 and Ca3Co2O6

The observation of unusual metastable behavior in ${\mathrm{Ca}}_{3}{\mathrm{Co}}_{2}{\mathrm{O}}_{6}$ remains an ongoing puzzle. When the magnetic field is increased at certain very slow rates, evenly spaced steps occur in the magnetization and other physical quantities as a function of magnetic field every 1.2 T. The ground state without steps is approached by slow relaxation processes over hours to days. It is a striking example of extremely slow dynamics arising from geometrical frustration in an otherwise clean and long-range ordered system, and its precise description remains controversial. Here we shed light on the mystery by reporting similar behavior in isostructural ${\mathrm{Ca}}_{3}{\mathrm{Co}}_{2\ensuremath{-}x}{\mathrm{Mn}}_{x}{\mathrm{O}}_{6}$, albeit at magnetic field sweep rates that are six orders of magnitude faster than that in ${\mathrm{Ca}}_{3}{\mathrm{Co}}_{2}{\mathrm{O}}_{6}$. We observe these steps not only in the magnetization, but also in the magnetostriction, electric polarization, and magnetocaloric effect. We present a study of metastable behavior in both compounds across seven orders of magnitude of magnetic field sweep rates using unique magnets at the National High Magnetic Field Laboratory. The metastable steps occur for intermediate ranges of magnetic field sweep rates, vanishing or evolving for the fastest and slowest sweep rates. Our data support that these metastable steps are an intrinsic feature of the three-dimensionally frustrated geometry of Ising spins in this structural family and thus narrow the number of applicable models.