Magnetocapacitance in geometrically frustrated magnet ZnFe ₂O₄

We report the measurement of dielectric constant in ZnFe₂O ₄ as a function of temperature and magnetic field. The behavior of dielectric constant for single crystals, which is dominated by the pair correlation of the neighboring Fe spins, indicates that ferromagnetic correlation is enhanced below 30 K, but is suppressed below 10 K, where positive magnetocapacitance is enhanced. It is also found that the magnetocapacitance of polycrystalline samples is much larger (∼ 10% at 14 T) than that of single crystals, because of the additional dielectric relaxation coupled with a uniform magnetization.