Coercivity Enhancement of Hexagonal Ferrites

Abstract

Hexagonal ferrites have been widely used as permanent magnets since their discovery in the 1950s. In spite of their relatively modest magnetic properties, ferrite magnets still show the best performance-to-cost ratio and different investigators are trying to improve their magnetic capabilities by using different synthesis methods and compositions. Different scientific investigations and techniques (Mössbauer spectrometry, X-ray diffraction, and magnetic measurements) have allowed to optimize the permanent magnet properties of rare earth substituted hexagonal ferrite magnets such as La-Co and Nd-Co Sr and Ba ferrites. However, the solubility of rare earth ions in M-type hexaferrite 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. We report results on enhanced coercivity of hexagonal Sr ferrites with Nd-Co substitution synthesized by the self-combustion method and calcination at 1100°C for two hours. The synthesis of this kind of ferrite is performed with a deficient, non-stoichiometric iron content (ratio Fe/ Sr1xRxof 10 and 11 instead of 12) in order to explore the presence of secondary phases. Comparison with samples of the same composition and stoichiometric formulation is made. Samples with lower iron content show the highest saturation magnetization, remanence and/or coercivity, indicating that the best results for applications of this ferrite will be obtained with an iron deficiency in the stoichiometric formulation. Nd substitution enhances the ferrite anisotropy and coercivity with respect to the unsubstituted sample.

Radiation losses in the microwave Ku band in magneto-electric nanocomposites

“…Also, at the nano-scale, its optical properties [19], magnetic properties [20–21], piezo-electric properties [22], photocatalytic properties [23], gas-sensing properties [24], electrical properties, dielectric properties [25–26], and mechanical properties [27] are better than those of the bulk material. Hexaferrite is also extensively studied by researchers for radiation absorption which is based on magnetic resonance phenomena because of the anisotropy field [10,28].…”

Gallium-substituted X-type hexagonal ferrites Sr2Co2GaxFe28−xO46: effect of substitution and heating temperature on phase formation and magnetic and dielectric properties

“…Furthermore, sintering of ferrites at such high temperatures results in grain growth, also contributing to such low coercive fields. 42,43 The trends in H C are shown in Fig. 7(b).…”

Estudio del dopaje y caracterización de hexaferrita de estroncio con Gd+3 obtenida mediante mecanosíntesis

“…Aceptando que el Gd 3+ sustituye al Sr 2+ en posiciones intersticiales tipo 2b (como se muestra en la Figura 3), para mantener la neutralidad iónica del compuesto, se deberán de crear vacancias, debido a que el Gd 3+ está aportando una carga extra por cada sustitución. [9][10] Por lo anterior, por cada 3 iones de Gd 3+ ocupando posiciones del Sr 2+ , se genera una vacancia de Fe 3+ , para mantener la electroneutralidad, expresado de acuerdo a la notación de Kröger-Vink se define:…”