A systematic Mössbauer spectroscopy study of Y3Fe5O12 samples displaying different magnetic ac-susceptibility and electric permittivity spectra

•The frequency dependence of χ and ∊ of Y3Fe5O12 (YIG) was measured.•Only YIG samples annealed below 1470 °C exhibit dispersion in the kHz region.•Broad Mossbauer spectra (MS) are observed in YIG samples without dispersion.•For dispersionless YIG the MS of the 24d Fe-site were analyzed with 5 subsextets. A comparative study of dielectric, specific heat, and magnetic properties has been carried out between bulk Y3Fe5O12 (YIG) samples which display different behavior regarding the dielectric and ac-susceptibility spectra. Experimental results are presented from two categories of YIG samples (called sample-A and sample-B). Sample-A exhibits zero imaginary part χ″(T) of the magnetic ac susceptibility whereas sample-B exhibits χ″(T) curves with two well defined broad maxima in the kHz region. These two maxima can be assigned to two different relaxation regimes. The frequency dependence of real (ε′) and imaginary (ε″) dielectric permittivity of sample-B reveals step-like transitions in ε′ and local maxima in ε″ at the kHz region, which are indicative for several relaxation processes. These processes are not observed in the electric permittivity of sample-A, indicating that dielectric and magnetic relaxation effects depend strongly on the preparation conditions of YIG. Such a completely different spectral behavior among YIG samples corresponds to a direct shape change of absorption sextets in Mössbauer spectra (MS). It was discovered that samples without dispersion in magnetic susceptibility and electric permittivity exhibit MS with distinct broadening of absorption lines in tetrahedral sites, as compared with samples that display dispersion. Moreover, Mössbauer spectroscopy for both categories of samples does not provide evidence for the presence of Fe2+.