Significant magneto-dielectric effect in SrNd2Fe2O7 at room temperature.

Here, we report the growth of (Sr, Ca) Nd₂Fe₂O₇ single crystals with the Ruddlesden–Popper structure using an optical floating-zone method. A significantly anisotropic magneto-dielectric effect (MD), ab-plane and c-axial MD coefficients reaching −12.3% and −8.4% measured at 10³ Hz in a 1 T magnetic field, can be obtained in a SrNd₂Fe₂O₇ crystal at room temperature. The corresponding anisotropic MD ratio can be reached as high as 1.46. With an increase in the Ca concentration, the MD effect decreases dramatically and is eventually completely suppressed in both directions. Analysis of magnetic properties and ⁵⁷Fe Mössbauer spectra suggests that the anisotropic MD effects in SrNd₂Fe₂O₇ can be attributed to polaronic hopping between two neighboring Fe³⁺ ions through oxygen vacancies in an anisotropically antiferromagnetic matrix; the disappearance of the MD effect in Ca-doped SrNd₂Fe₂O₇ is a consequence of the suppression of the antiferromagnetism. Our work suggests that the significantly anisotropic MD effect in SrNd₂Fe₂O₇ crystals at room temperature can be used in magneto-dielectric controlled devices. [ABSTRACT FROM AUTHOR]