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

The direct ordering of amorphous or disordered nanoparticles without high-temperature post-annealing is of rattling significance for their controllable synthesis and property improvement but still remains challenging. In this work, the effect of substrate bias-voltage (BV) on direct crystallization ordering and magnetic properties of Sm-Co-X nanoparticles fabricated by cluster beam deposition (CBD) method is explored. It is found that the applying BV within ±4 kV does not affect the shape and size of final deposited nanoparticles. As the BV increases, the coercivity and remanence ratio of Sm-Co-Ni nanoparticle films are significantly improved, which should be originated from the better crystallinity of nanoparticles upon landing after applying the BV. Further investigations are carried out on the thick Sm-Co-Ni nanoparticle films with various thicknesses at a fixed BV of +1 kV. The appreciable coercivity of 6.1 kOe at room temperature is achieved for appropriate thickness without thermal annealing. The composition and structure of Sm-Co-Ni nanoparticles are characterized by transmission electron microscopy (TEM). It is found that all three elements has a homogeneous distribution in the nanoparticle and no surface segregation is observed. The better crystallinity of Sm-Co-Ni after applying BV is also confirmed by TEM observation. Our results demonstrate that the high BV may serve as a novel way for ordering the amorphous or disordered nanoparticles without shape and size change with no necessity of high-temperature annealing.