Microstructural and Magnetic Properties of Core-Shell Ni-Ce Nanocomposite Particles Assemblies
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Microstructural and Magnetic Properties of Core-Shell Ni-Ce Nanocomposite Particles Assemblies Xiang-Cheng Sun1*, J. A. Toledo1 and M. Jose Yacaman2 1
Prog. Simulación Molecular, Instituto Mexicano del Petróleo, Lázaro Cárdenas 152#, 07730, D.F. México, México 2 ININ, Amsterdam No.46-202, Col. Condesa 06100, D. F. México, México * E-mail: [email protected] ABSTRACT Novel magnetic core-shell Ni-Ce nanocomposite particles (15-50 nm) are presented. SEM observation indicates a strongly ferromagnetic interacting order with chain-like features among Ni-Ce nanocomposite particle assemblies. Typical HREM image demonstrates that many planar defects (i. e. stacking faults) exist in large Ni core zone (10-45 nm ); the innermost NiCe alloy and outermost NiO oxide exist in the thin shell layers ( 3-5 nm ) . Nano-diffraction patterns show an indication of well-defined spots characteristic and confirm the nature of this core-shell nanocomposite particles. Superparamagnetic relaxation behavior above average blocking temperature (TB =170K) for Ni-Ce nanocomposite particles assemblies have been exhibited, this superparamagnetic behavior is found to be modified by interparticle interactions, which depending on the applied field; size distribution and coupling with the strong interparticle interaction. In addition, an antiferromagnetic order occurs with a Neél temperature TN of about 11K due to Ce ion magnetic order fuction. A spin-flop transition is also observed below TN at a certain applied field and low temperature. INTRODUCTION Magnetic nanoparticles have been an active subject of intense research due to their unique magnetic properties that are appealing from both scientific and technological points of view [13]. Specifically, metallic (Fe, Co, Ni, etc) [3-6] and oxide (γ-Fe2O3, etc) [4] magnetic nanoparticles have attracted considerable attention as high-density magnetic storage media because a high coercive force and a high saturation magnetization can be achieved. Recently, experimental evidences for low temperature superparamagnetism relaxation [7] and the ordering of spin-glass like behavior [4, 8] in some single domain magnetic particles (i.e. γ-Fe2O3 ) had also been of significant interest. In this study, novel Ni-Ce nanocomposite particles coated with NiCe alloy and NiO oxide shell layers were prepared. Their unique microstructure features and superparamagnetic order properties will be reported here. EXPERIMENTAL The Ni-Ce particle nanocomposite were prepared by the plasma-metal reaction technique [9]. A JEOL-4000EX high-resolution transmission electron microscope (HRTEM) was used to
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determine the detailed core-shell phase and average grain size of the particle. It also allows recording selected area electron nano-diffraction patterns. A Phillips XL30 scanning electron microscope ( SEM ) equipped with X-ray energy-dispersive analysis (EDX) system, was employed to provide the morphology of particles and chemical analysis. The magnetization measurements were performed by using SQUID magnetometer in the temp
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