Facile synthesis and magnetic phase transformation of Nd–Fe–B nanoclusters by oxygen bridging

Abstract

We demonstrate a facile chemical approach for fabricating Nd–Fe–B nanoclusters through oxygen bridging. The Nd–Fe–B nanoclusters comprised of small aggregated particles (∼2 nm diameter) could be successfully synthesized using sodium borohydride, a conventional reducing agent. The three-step process consists of the formation of Fe–B primary particles through borohydride reduction and the reduction of Nd cations over the Fe–B particles under hydrophilic conditions in coordination with oxygen. Finally, a reductive annealing process in an H₂ atmosphere allowed the oxidized Nd phase in Nd–Fe–B nanoclusters to be reduced and diffuse into the Fe–B primary phase to form ternary Nd₂Fe₁₄B intermetallic nanoparticles. The magnetic behaviors of both the primary Nd–Fe–B nanoclusters and the final intermetallic Nd₂Fe₁₄B phase have been studied. Through reductive annealing, the as-grown amorphous Nd–Fe–B nanoclusters of soft magnetic behaviour could be transformed to a crystalline intermetallic Nd₂Fe₁₄B phase of highly ferromagnetic nature. The mechanism of formation of the lanthanide based intermetallic phase has been discussed. The proposed method of synthesis can lead to a simple route for the otherwise difficult fabrication of lanthanide-based intermetallic ternary nanostructures.