Synthesis and magnetic properties of core-shell structured (NiCo)O(AFM)-NiCo(FM) magnetic nanoparticles

• Published in: IEEE transactions on magnetics Vol. 38; no. 5; pp. 2595 - 2597
• Main Authors: Jeyadevan, B., Chinnasamy, C.N., Perales-Perez, O., Iwasaki, Y., Hobo, A., Shinoda, K., Tohji, K., Kasuya, A.
• Format: Journal Article Conference Proceeding
• Language: English
• Published: New York, NY IEEE 01-09-2002; Institute of Electrical and Electronics Engineers; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Anti-freeze; Antiferromagnetic materials; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Crystalline materials; Exact sciences and technology; Magnetic anisotropy; Magnetic cores; Magnetic materials; Magnetic properties; Magnetic properties and materials; Magnetic properties of nanostructures; Magnetic recording; Magnetism; Nanoparticles; Perpendicular magnetic anisotropy; Physics; Scanning electron microscopy; Chemical precipitation; Experimental study; Cobalt; STM; Nanoparticles; Magnetization curve; exchange-bias; Transmission electron microscopy; polyol process; nanocrystalline Ni-Co particles; Monodispersed particle; Nickel; Polyol; Core-shell structured nanoparticles; Chemical synthesis; Nanotechnology; Magnetic properties
• ISSN: 0018-9464; 1941-0069
• DOI: 10.1109/TMAG.2002.803219

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 (H/sub E/) 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 H/sub E/ field of 36 and 201 Oe at 298 and 77 K, respectively.