Mössbauer spectral evidence for rhombohedral symmetry in R₃Fe₅O₁₂garnets with R = Y, Eu and Dy

Abstract

The iron-57 Mössbauer spectra of R3Fe5O12, where R is Y, Eu and Dy, have been measured between 4.2 and 550 K. The substantial quadrupole splittings observed in the paramagnetic spectra confirm that the local symmetry at both the tetrahedral and octahedral iron(III) sites is not cubic. The low temperature Mössbauer spectra of Dy3Fe5O12 clearly confirm the spin reorientation between 10 and 15 K and the 4.2 and 10 K spectra are consistent with the known orientation of the magnetization at 14 K in the cubic Ia3̄d unit cell. The Mössbauer spectra of R3Fe5O12, where R is Y, Eu and Dy, obtained between 45 and 295 K, reveal four different tetrahedral iron(III) Mössbauer spectral components, four components which are inconsistent with a magnetization oriented along the [111] axis of a cubic Ia3̄d unit cell. In contrast, these four components are consistent with a crystal symmetry which is reduced from cubic to rhombohedral R3̄. The temperature dependence of the hyperfine fields in Dy3Fe5O12 indicates a small biquadratic exchange contribution to the magnetic exchange. The temperature dependence of the isomer shifts in Dy3Fe5O12 gives Mössbauer lattice temperatures of 405 and 505 K for the 16a and 24d sites, respectively, values which are in excellent agreement with the Debye temperature measured for Y3Fe5O12.

Defect formation in Gd3Fe5O12-based garnets: a Mössbauer spectroscopy study

“…The Mfssbauer spectrum of Gd 3 Fe 5 O 12 (Fig. 3A) is similar to those reported for rare-earth iron garnet ferrites [13][14][15]. It was successively fitted with either two or three sextets.…”

“…The first model implied that Fe 3+ on each site, tetrahedral and octahedral, contributes with one sextet to the spectrum. According to [14,15], the different orientations of the main axis V zz of the electric field gradient and the magnetic hyperfine field B hf on the octahedral sites should give rise to two sextets with the same IS and quadrupole splittings QS, slightly different B hf , and with a relative area ratio of 3:1. For Ia3d symmetry, the angle between V zz and B hf on the tetrahedral sites is always the same and therefore only one sextet is expected for this site.…”

“…A more complex refinement with a total of six sextets resulting from a rhombohedral distortion of the Ia3d symmetry, as described in Ref. [15] for R 3 Fe 5 O 12 (R=Y, Eu, Dy), was also attempted, but no further improvement of the refinement quality was achieved. The values obtained by the three-sextet fit are summarized in Table 2.…”

Low temperature spin reorientation in dysprosium iron garnet

“…At this first order transition temperature T SR a drastic change of the real structure is expected: the rhombohedral distorsion of the R 3 c space group with only two inequivalent magnetic sites [9] is no longer valid below T SR and the symmetry is lowered with the appearance of at least four inequivalent sites of the monoclinic space group C2/c [6]. The more recent study of the Mössbauer spectra of DyIG [11] clearly confirm also that the SR phase transition occur at 15 K down 4.2 K but reveal in the 45 K-295 K temperature range, that the Mössbauer spectral components are consistent with a crystal with a reduced symmetry from cubic to rhombohedral but with the space group R 3 . From the detailed of the magnetisations measurements in low and high magnetic fields and the neutron diffraction experiments, only two types of essential properties are presented in this discussion: is used in the representation analysis of Bertaut [13].The opening of the double umbrella magnetic structure is followed by an increase of the rhombohedral distorsion which modify the cubic description G 4g (T 1g )®A 2g and the crystallographic and magnetic glide planes c and c' respectively are conserved.…”

Enhancement in Curie Temperature of Yttrium Iron Garnet by Doping with Neodymium

“…This trigonal axis coincides with the [111] direction. Finally, the third tetrahedral site also contains Fe 3+ ions (24d) [5,6,7,8]. The substitution of Y 3+ by magnetic rare earth ions promotes the formation of a new magnetic sub-lattice, which in turn causes the material to have a compensation point below room temperature [9,10].…”