Rare‐Earth‐Substituted Sr_1−xLn_xFe₁₂O₁₉ Hexagonal Ferrites

Abstract

A systematic study on the phase formation and magnetic properties of M‐type hexagonal ferrite solid solutions Sr1−xLnxFe12O19 with rare‐earth ions Ln=Pr, Nd, Sm, Eu, and Gd was performed. All ferrite samples were prepared by the mixed oxide route and characterized with a combination of powder XRD, microscopy, electron‐probe microanalysis, and thermal analysis. For Ln=Pr, Nd, and Sm, the formation of M‐type ferrite solid solutions with limited solubility of rare earths was observed. The lattice parameters of Sr1−xLnxFe12O19 exhibit a linear variation with x within the range of ferrite solid solution, i.e., c0 decreases with x. For Eu‐ and Gd‐containing samples substituted X‐type ferrites are observed. The solubility limits of the rare‐earth ions within the M‐type ferrite lattice range from x=0.46 for Pr to about x=0.17 for Sm. Eu and Gd can be substituted to lesser amounts in the X‐type ferrites. The saturation magnetization at T=5 K increases with increasing rare‐earth concentration for Pr, Nd, and Sm. Mössbauer spectrometry reveals signals originating from Fe3+ on five different crystallographic positions of the M‐type structure as well as ferrous ions on Fe 2a sites. The spectra of the hexagonal ferrites with different rare‐earth ions (La, Pr, Nd, Sm) are very similar and show systematic variations of the hyperfine fields with rare‐earth concentrations.

Preparation and Magnetic Properties of Nd–Co-Substituted M-Type Strontium Ferrite by Microwave-Assisted Synthesis Method

“…One hand, the existence of α-Fe 2 O 3 phase in Nd-Co-cosubstituted strontium ferrites at x = y = 0.05 could dilute the σ s and σ r [23]. On the other hand, in order to maintain the electric neutrality, the Sr 2+ replaced by Nd 3+ is associated with the valence change from Fe 3+ (high spin, 5 μB) to Fe 2+ (low spin, 4 μB) on the 2a sites [24], accompanying with spin canting deviated from the collinear to noncollinear arrangement and the weaker superexchange of Fe 3+ -O 2− -Fe 2+ . The above aspects tend to decrease the net magnetic moment, which results in the reduction of σ s and σ r .…”

Synthesis of M-type SrFe12O19 by mechanosynthesis assisted by spark plasma sintering

“…Luo [14] prepared strontium hexaferrite by mechanosynthesis of a mixture of SrCO 3 route was reported by Sharma et al [16] to obtain barium hexaferrite. By setting up the same experimental parameters they reported certain enhancement in some magnetic properties; such as the saturation magnetization and coercivity.…”

“…Although many other hard magnetic materials have been developed after these years, the hexaferrite performance/cost ratio is still extremely favorable. The unit cell of these of ferrites consists of a spinel block (S) with two layers of four oxygen atoms with three divalent metal ions between each layer in four octahedral sites, where the cation is surrounded by six oxygen anions and two tetrahedral sites where four oxygen anions surround the cations; and a block (R) (with the stoichiometry (SrFe 6 O 11 ) À2 ) with three hexagonally packed layers of four oxygen atoms each, but one of the oxygen atoms in the center layer is replaced by a similarly sized divalent metal atom with an overlap of hexagonally and cubically packed layers [3].…”

A Mössbauer investigation of Sr1−xLaxFe12O19 (0≤x≤1) M-type hexaferrites

“…However the solubility of Ln ions in Sr-hexaferrites is very low and their introduction leads to the formation of secondary phases which must be avoided in order to obtain permanent magnets with optimal properties [9,11]. The presence of Co increases the solubility of the rare earth ion [10] but no single-phase Ln(Fe,Co) 12 O 19 hexaferrites have been synthesised up to now.…”