Local Magnetic Properties of Spinel Cd_(0.9)M_(0.1)Fe_2O_4(M = Zn, Ni) Investigated by Using External Magnetic Field M¨ossbauer Spectrometry

Cd_(0.9)M_(0.1)Fe_2O_4 (M = Zn, Ni) ferrites, prepared by the solid state reaction method, have been studied by x-ray diffraction and Mössbauer spectroscopy. The lattice constants are determined to be a_0 = 8.686 Å for Cd_(0.9)Zn_(0.1)Fe_2O_4 and a_0 = 8.664 Å for Cd_(0.9)Ni_(0.1)Fe_2O_4 with a cubic spinel structure. Zero-field Mössbauer spectra of the samples were taken at various temperatures ranging from 4.2 to 295 K. A line broadening arising from the relaxation effect was observed below Néel temperature (T_N). The Néel temperatures of samples are determined to be 18 K for Cd_(0.9)Zn_(0.1)Fe_2O_4 and 40 K for Cd<SUB>0.9</SUB>Ni<SUB>0.1</SUB>Fe<SUB>2</SUB>O<SUB>4</SUB>. Mössbauer spectra were fitted to one magnetic component for Cd<SUB>0.9</SUB>Zn<SUB>0.1</SUB>Fe<SUB>2</SUB>O<SUB>4</SUB> and two magnetic components for Cd<SUB>0.9</SUB>Ni<SUB>0.1</SUB>Fe<SUB>2</SUB>O<SUB>4</SUB>. At 4.2 K, the magnetic hyperfine fields were <I>H</I><SUB>hf</SUB>(<I>B</I>) = 484 kOe for Cd<SUB>0.9</SUB>Zn<SUB>0.1</SUB>Fe<SUB>2</SUB>O<SUB>4</SUB> and <I>H</I><SUB>hf</SUB>(<I>A</I>) = 485 kOe and <I>H</I><SUB>hf</SUB>(<I>B</I>) = 503 kOe for Cd<SUB>0.9</SUB>Ni<SUB>0.1</SUB>Fe<SUB>2</SUB>O<SUB>4</SUB>. The isomer shift values at room temperature are <I>d</I> = 0.24 - 0.25 mm/s, indicating that the valence state of Fe ions are ferric in tetrahedral and octahedral coordination. The low-temperature magnetic behaviors of these samples were also investigated with the external-field Mössbauer spectrometer at 4.8 T, showing the localized spin canting at both <I>A</I> and <I>B</I> sites of Cd<SUB>0.9</SUB>Ni<SUB>0.1</SUB>Fe<SUB>2</SUB>O<SUB>4</SUB> with the average canting angles of 51˚ and 43˚ at 4.2 K.