Transient magnetic states in the multiferroic frustrated spin chain compound Ca$_{3}$CoMnO$_{6}$

We report the discovery of transient magnetic states in a frustrated Ising spin chain system Ca$_{3}$CoMnO$_{6}$ that are observed only within a certain range of magnetic field ($B)$ sweep rates. Spin chains are composed of alternating Co$^{2+}$ and Mn$^{4+}$ spins along the $c$-axis and arranged in a triangular lattice in the \textit{ab}-plane. At zero field, the spins order in a $\uparrow \uparrow \downarrow \downarrow $ configuration that allows for ferroelectric polarization ($P)$. Previous work shows that when DC field is applied along the $c$-axis, a $\uparrow \uparrow \uparrow \downarrow $ spin structure with a 1/2 magnetization ($M)$ plateau is stabilized around $B$ $\sim$ 15 T and $P$ disappears. However, when applying $B$ with various sweep rates using a 60 T shaped-pulse magnet we find transient features in the $M$, $P$, and magnetostriction ($\Delta L$/$L)$. We found one step at 4 T with sweep rate of 75 T/s and another step at 6 T when further increasing the rate to 960 T/s, both below the $M=$1/2 plateau. We attribute this time dependence to the magnetic frustration from both interchain and intrachain exchange interactions between Ising-like Co$^{2+}$ spins which can leads to the creation of magnetic microphases. Thus the evolution of $M$ with external parameters is not a straightforward canting or rotation of spins, but could be a progression through many different ordered microphases that are close in energy. This strongly suggests that an ANNNI-like model is appropriate to describe this system.