Limit on the Electron Electric Dipole Moment Using Paramagnetic Ferroelectric Eu0.5Ba0.5TiO3

We report on the results of a search for the electron electric dipole moment d_e using paramagnetic ferroelectric Eu_0.5Ba_0.5TiO₃. The electric polarization creates an effective electric field that makes it energetically favorable for the spins of the seven unpaired 4f electrons of the Eu²⁺ to orient along the polarization, provided that d_e≠0. This interaction gives rise to sample magnetization, correlated with its electric polarization, and is therefore equivalent to a linear magnetoelectric effect. A SQUID magnetometer is used to search for the resulting magnetization. We obtain d_e=(-1.07±3.06_stat±1.74_syst)×10^-25ecm, implying an upper limit of |d_e|<6.05×10^-25ecm (90% confidence).