resumo
It has recently been reported that, in FePt nanoparticles (NPs) protected by poly(N-vinyl-2-pyrrolidone) (PVP), which possess a particle diameter (D) near the critical size (2-3 nm) for the emergence of the face-centered tetragonal (fct) structure, the coercive field (H-c) at room temperature increases with increasing D, whereas the H-c value below 10 K increases with decreasing D. We investigated the fct-ordering parameter (S) for PVP-coated FePt NPs with three mean D values (= 2.0, 2.6, and 3.4 nm) in order to gain a better insight into the unique behavior of H-c. Furthermore, the temperature dependencies of H-c, saturation magnetization (M-s), and their product (HcMs) were also investigated. The behavior of H-c at high temperature is attributed to the decrease in the magnetic switching volume (V), while the enhancement of H-c at low temperatures with decreasing D is thought to originate from the decrease in the saturation magnetization, M-s, with decreasing D. The decrease in M-s with decreasing D is related to the decrease in the fct-ordering. (C) 2010 American Institute of Physics. [doi:10.1063/1.3524190]
palavras-chave
MAGNETIC-PROPERTIES; SIZE DEPENDENCE; TEMPERATURE; ALLOYS; PHASE
categoria
Physics
autores
Mito, M; Komorida, Y; Silva, NJO; Tsuruda, H; Deguchi, H; Takagi, S; Tajiri, T; Iwamoto, T; Kitamoto, Y
nossos autores
Nuno João Silva
Investigador Principalagradecimentos
This work was supported by a Grant-in-Aid for Young Scientists (B) Grant No. 19750118) from the MEXT of Japan. N.J.O.S. acknowledges the FCT for the Ciencia 2008 program.