Review and prospect of ferroelectricity and magnetism in YMn₂O₅

YMn₂O₅ undergoes ferroelectric successive phase transitions at 39 K and 19 K, in which a dielectric constant shows anomalies. Spontaneous polarization was also observed. Just above these ferroelectric phase transition temperatures, at 45 K, antiferromagnetic order occurs. Neutron elastic measurements and magnetic susceptibility measurements reveal that the ferroelectric phase transition at 39 K and 19 K occurs simultaneously with the change of magnetic ordering pattern. Review of experimental results and conjecture for the origin of spontaneous polarization are given.