Abstract
Recent studies on next-generation permanent magnets have focused on filling in the gap between rare-earth magnets and rare-earth-free magnets, taking into account both the cost-effectiveness and magnetic performance of the magnetic materials. As an improved rare-earth-free magnet candidate, here, Ca-substituted M-type Sr-lean hexaferrite particles within a nano- to micro-scale regime, produced using an ultrasonic spray pyrolysis method, are investigated. Theoretically, the maximum coercivity (Hc) can be achieved in submicron Sr-ferrite crystals (i.e., 0.89 μm). The plate-like resultants showed a significant enhancement in Hc, up to a record high of 7880.4 Oe, with no deterioration in magnetization (M: 71–72 emu/g). This resulted in more favorable magnetic properties than those of the traditional Sr–La–Co ferrites. On the basis of microstructural analysis and fitting results based on the law of approach to saturation method, the Ca-substitution effects on the change in size and anisotropic characteristics of the ferrite particles, including pronounced lateral crystal growth and a strong increase in magnetocrystalline anisotropy, are clearly demonstrated. The cost-effective, submicron, and Ca-substituted Sr-ferrite is an excellent potential magnet and moreover may overcome the limitations of traditional hard magnetic materials.
Highlights
Recent studies on next-generation permanent magnets have focused on filling in the gap between rare-earth magnets and rare-earth-free magnets, taking into account both the cost-effectiveness and magnetic performance of the magnetic materials
The calcined samples were rinsed with distilled water to remove most of the residual NaCl, and were dried overnight in a vacuum oven. (See the phase and morphology of the synthesized particles in Fig. S1b and c, respectively.) The overall procedure was slightly modified from a previous method that we describe in detail e lsewhere[7,22]
As the amount of Ca increased up to 0.40, there was a noticeable change in the thickness, and in the diameter of the Sr-ferrite particles, while they became more plate-like in shape with a high aspect ratio, up to 9.31
Summary
Recent studies on next-generation permanent magnets have focused on filling in the gap between rare-earth magnets and rare-earth-free magnets, taking into account both the cost-effectiveness and magnetic performance of the magnetic materials. As an improved rare-earth-free magnet candidate, here, Ca-substituted M-type Sr-lean hexaferrite particles within a nano- to micro-scale regime, produced using an ultrasonic spray pyrolysis method, are investigated. The plate-like resultants showed a significant enhancement in Hc, up to a record high of 7880.4 Oe, with no deterioration in magnetization (M: 71–72 emu/g). This resulted in more favorable magnetic properties than those of the traditional Sr–La–Co ferrites. -called “gap magnets” have been introduced as a compromise to fill the gap between RE magnets and RE-lean magnets, given both their lower material costs and good magnetic performance[2,3] In this regard, elemental substitution should enhance Hc without sacrificing the M value. The application of spray pyrolysis in a salt matrix for the synthesis of single crystals with exquisitely controlled homogeneity has become an attractive research a rea[22]
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