Magnetic property improvement and crystallization tuning of cluster-beam-deposition-fabricated Sm-Co-X nanoparticles via bias voltage

The direct ordering of amorphous or disordered nanoparticles without high-temperature post-annealing is of great significance for their controllable synthesis and improvement of their properties; however, it remains challenging. In this work, the effects of substrate bias voltage (BV) on the direct crystallization ordering and magnetic properties of Sm-Co-X nanoparticles fabricated by cluster beam deposition (CBD) were explored. It was found that applying BV within +/- 4 kV did not affect the shape and size of the final deposited nanoparticles. As BV increased, the coercivity and remanence ratio of the Sm-Co-Ni nanoparticle films were significantly improved, which originated from the better crystallinity of the nanoparticles upon landing after applying BV. Further investigations were carried out on thick Sm-Co-Ni nanoparticle films with various thicknesses at a fixed BV of +1 kV. Appreciable coercivity of 6.1 kOe at room temperature was achieved for appropriate thickness without thermal annealing. The composition and structure of the Sm-Co-Ni nanoparticles were characterized by transmission electron microscopy (TEM). It was found that all three elements were homogeneously distributed in the nanoparticles, and no surface segregation was observed. The better crystallinity of Sm-Co-Ni after applying BV was also confirmed by TEM observations. Our results demonstrate that applying high BV may serve as a novel way for ordering amorphous or disordered nanoparticles without shape and size changes without the necessity of high-temperature annealing.