Abstract
Nanocapsules consisting of B 2O 3/H 3BO 3 encapsulating Fe–Gd cores have been synthesized by an arc-discharge process using metal–boron alloys as cathode. Most of the nanocapsules have a well-constructed shell/core structure with a uniform B 2O 3/H 3BO 3 shell. Heat-treatment induces reactions between the shell and the core, resulting in the formation of a Fe 3BO 5+GdBO 3 matrix embedded with Fe nanoparticles, reduction of the metallic-core size and decrease of the blocking temperature T B. Above T B, the magnetization curves plotted vs. H/T overlap and show zero coercivity. Below T B, the coercivity shows a linear dependence when plotted vs. T 1/2. However, the coercivity- T 1/2 curve below 60 K has a different slope from that above 60 K, indicating the existence of two different magnetic phases in the nanocapsules. Different from bulk Fe 3BO 5, nanoscale Fe 3BO 5 particles have a lower transition temperature to the weak-ferromagnetic state, and magnetic hysteresis is absent due to size effects.
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