Title :
Synthesis and magnetic properties of core-shell structured (NiCo)O(AFM)-NiCo(FM) magnetic nanoparticles
Author :
Jeyadevan, B. ; Chinnasamy, C.N. ; Perales-Perez, O. ; Iwasaki, Y. ; Hobo, A. ; Shinoda, K. ; Tohji, K. ; Kasuya, A.
Author_Institution :
Tohoku Univ., Sendai, Japan
fDate :
9/1/2002 12:00:00 AM
Abstract :
We have succeeded in the synthesis of nanometer size monodispersed Ni-Co metal particles through the modified-polyol process. Ni-Co metal particles of about 40 and 100 nm with Co-rich core and Ni-rich shell were produced by the manipulation of the reaction kinetics through a suitable selection of hydroxyl ion concentration in the ethylene glycol-Ni-Co system. Furthermore, core-shell structured (NiCo)O(AFM)-NiCo(FM) was produced by oxidizing particles at 533 K in air for different times. The magnetic properties, especially the exchange-bias (HE) fields of 40 and 100-nm core-shell structured particles synthesized under similar conditions behaved differently. However, their behavior was explained considering exchange biased interactions at (NiCo)O(AFM)-NiCo(FM), and (Co)O(AFM)-Co(FM) interfaces with two different exchange coupling constants. The 40 nm particles oxidized for 4 h and composed of (NiCo)O(AFM)-NiCo(FM), exhibited a maximum HE field of 36 and 201 Oe at 298 and 77 K, respectively.
Keywords :
X-ray chemical analysis; X-ray diffraction; annealing; antiferromagnetic materials; atomic force microscopy; cobalt alloys; cobalt compounds; coercive force; exchange interactions (electron); ferromagnetic materials; interface magnetism; magnetic hysteresis; magnetic particles; nickel alloys; nickel compounds; oxidation; powder technology; scanning electron microscopy; transmission electron microscopy; (NiCo)O-NiCo; 298 K; 40 to 100 nm; 533 K; 77 K; M-H loop; SEM; TEM-EDX; X-ray diffraction patterns; annealing; antiferromagnetic-ferromagnetic exchange; core-shell structured magnetic nanoparticles; exchange-bias fields; hydroxyl ion concentration; magnetic interfaces; magnetic properties; microstructure; modified-polyol process; monodispersed particles; oxidation; reaction kinetics; saturation magnetizations; synthesis; Anti-freeze; Antiferromagnetic materials; Crystalline materials; Magnetic anisotropy; Magnetic cores; Magnetic materials; Magnetic properties; Magnetic recording; Nanoparticles; Perpendicular magnetic anisotropy;
Journal_Title :
Magnetics, IEEE Transactions on
DOI :
10.1109/TMAG.2002.803219
