Spin Canting in Silica-Coated Nickel Ferrite (NiFe2O4@SiO2) Nanoparticles: a Mössbauer Spectroscopy Study

Tuning Physical Properties of NiFe2O4 and NiFe2O4@SiO2 Nanoferrites by Thermal Treatment

“…As the authors noted, the canting angle for a sample with a crystallite size of 9 nm is about 48 deg, which is a bit larger than estimated by Chinnasamy et al [30] for the ball-milled sample with 10-nm-size particles (i.e., α YK ≈ 34 deg). The values of the saturation magnetization estimated for NFO nanoparticles are lower those for bulk NiFe 2 O 4 (55 emu/g) compound and other nanoparticles synthesized by different methods, e.g., by mechanosynthesis (M s = 24.4 emu/g) [24] or modified co-precipitation (M s = 49.7 emu/g), [35] in our case most likely due to the ultrafine structure of co-precipitated NFO. Thus, the increase of M S is generally thermally induced, and as was shown, the increase of the annealing temperature (T A ) is associated with the enhancement of the crystallization process, [13][14][15][16][17][18][19][20][21][22][23][24] causing the crystallites/grains growth affecting a decrease of a surface-to-volume fraction.…”

“…For 57 Fe Mo¨ssbauer spectrometry, the τ m value is in order of 10 −8 s. It is also worth mentioning that, as previously reported for spinel nanoferrites, the Mo¨ssbauer spectra strictly depend on the chosen synthesis type and further sample processing. [5,16,17,22,24,25,34,35] In the paper of Hoque et al, [16] the influence of annealing on various physical properties, including the crystallites size of NiFe 2 O 4, is reported. Thus, the approach used by the authors reveals the emergence of a doublet line related to the processing of samples from its as-dried form to annealed up to 400 °C corresponding to the crystallites size from 2 to 4 nm.…”

“…As reported, a sol-gel method was predominantly applied in preparing such nanocomposites based on, e.g., NiFe 2 O 4 , CoFe 2 O 4 , CuFe 2 O 4 , ZnFe 2 O 4 , (NiZn)Fe 2 O 4 and SiO 2 matrix. [35][36][37][38][39][40][41][42][43][44][45] One of the positive features of the sol-gel method is the homogeneous dispersion of NPs. Beyond preventing particle aggregation, the silica matrix is used in active catalytic applications, whereas a porous shell allows the transport of gases from and to the ferrite core.…”

“…Over the past few years, several studies have been done on NiFe 2 O 4 @SiO 2 nanoparticles synthesized mainly by sol-gel or ball-milling. [35][36][37][38][39][40][41][42][43][44][45] Mitra et al [39] for NiFe 2 O 4 NPs showed that the duration of heat treatment at different temperatures determines the particle size ≤ 25 nm. However, the superparamagnetic behavior dependent on the NPs size, in this case, was evidenced only at room temperature for particles < 10 nm.…”

“…Thereafter, Umut et al [35] studied the NiFe 2 O 4 @SiO 2 compounds with identical magnetic cores of about 5.83 ± 0.79 nm and two different silica shells of 9.7 ± 1.40 and 12.45 ± 0.95 nm. Both powdered samples were heated under N 2 conditions from room temperature up to 900 °C with 10 °C/min speed.…”