Full-angle spin rotation in multiferroic GdMn2O5

Recently, an unusual sequence of four topological states has been observed in multiferroic GdMn2O5. In these experiments, in ramping the external magnetic field up and down through the magnetic phase transition, the electric polarization of the sample passes through a cycle of four states, schematically represented as 1=>2=>3=>4=>1. In these experiments, the clockwise or counterclockwise sequence of states is protected by the geometry of the experiment, making them equivalent to a topological charge. A theoretical explanation of the observed effects suggests that half of the spins rotate by 360 degree with 90 degree in each step. The goal of this proposal is to observe the full-angle spin rotation with the field-induced XMCD.