We report on the effects of spin fluctuations, magnetic ordering, and external magnetic field on the dielectric constant of the ferromagnet ${\mathrm{S}\mathrm{e}\mathrm{C}\mathrm{u}\mathrm{O}}_3$, and the antiferromagnet ${\mathrm{T}\mathrm{e}\mathrm{C}\mathrm{u}\mathrm{O}}_3$. A model based on the coupling between uniform polarization and the $q$-dependent spin-spin correlation function is presented to explain the different behaviors for these isostructural compounds. The large magnetocapacitance near the transition temperature in the ferromagnet ${\mathrm{S}\mathrm{e}\mathrm{C}\mathrm{u}\mathrm{O}}_3$ suggests routes to enhancing the magnetodielectric response for practical applications.

• Received 16 May 2003

DOI:https://doi.org/10.1103/PhysRevLett.91.257208