Colossal Magnetodielectric Effects inDyMn2O5

We have investigated the detailed magnetic field dependence of the electric polarization and dielectric constant in $(\mathrm{T}\mathrm{b},\mathrm{D}\mathrm{y},\mathrm{H}\mathrm{o}){\mathrm{M}\mathrm{n}}_2{\mathrm{O}}_5$ where magnetic and ferroelectric transitions are intimately coupled. Our fundamental discovery is the unprecedented large change of the dielectric constant with magnetic field, particularly in ${\mathrm{D}\mathrm{y}\mathrm{M}\mathrm{n}}_2{\mathrm{O}}_5$, associated with an unusual commensurate-incommensurate magnetic transition. This extraordinary effect appears to originate from the high sensitivity of the incommensurate state to external perturbation.