Oriented magnetic nanowires with high coercivity

Abstract

CoNi magnetic nanowires with a mean diameter of 7 nm and a mean length in the range 100-300 nm have been prepared by reduction of a mixture of cobalt and nickel salts in a sodium hydroxide solution in a liquid polyol. The shape control is related to the particle growth rate which is strongly dependent on the basicity and on the Co-Ni composition. We show that high growth rate favours cobalt urchinlike particles while lower growth rate favours dumbbell-like bimetallic cobalt-nickel particles. Wire formation corresponds to an optimization of the growth conditions and is obtained in a narrow range of basicity and Co-Ni composition. Structural studies showed well crystallized wires with their long axis corresponding to the crystallographic c-axis of the hexagonal close-packed (hcp) phase. Multipods are also observed in which several wires have grown from a single nucleus presenting a cubic structure. Addition of surfactants (trioctyl phosphine and oleic acid) allows the modification of the wire surface and favours their dispersion in toluene. Square hysteresis curves are obtained on wires aligned under magnetic field and frozen in toluene or in PMMA with remanence to saturation ratio close to 1 and coercivity of 6.5 kOe. This value is much higher than was previously obtained on anisotropic particles prepared by the polyol process and results from an improvement of the shape control and the good crystallinity of the wires

Controlled metal nanostructures: Fertile ground for coordination chemists

“…For instance, G. Viau et al developed a "polyol" method using carboxylate precursors to obtain Co nanorods and nanodisks [60] or [Co x Ni 1-x ] (x=0.5-1) nanowires and nanorods [61]. M a n u s c r i p t 15 The key benefits result from the high reactivity of the M-N bond, absence of oxygen atoms (no risk of metal oxide formation) and facile thermal decomposition and reduction.…”

Synthesis of nanocrystalline Co–Ni alloys by precursor approach and studies on their magnetic properties

“…dumbbells) have been prepared by the reduction of cobalt and nickel acetates in a NaOH solution of 1,2-propanediol [36,37]. Co-Ni nanowires have been prepared by reduction of a mixture of metal salts in NaOH solution of a polyol and the shape was found to depend on NaOH concentration and the Co-Ni composition [6]. A modified polyol method has been reported in which stoichiometric amounts of metal nitrates were mixed with PVP and subjected to ethylene glycol reduction [38].…”

“…In the recent years, magnetic nanoparticles such as metals, alloys and multi-layers have attracted tremendous interest from researchers in many fields due to their promising applications in the area of ferro-fluids [1], microwave absorbance [2], hyperthermia [3], catalysis [4], magnetic resonance imaging (MRI) and drug delivery system [5], magnetic recording and magnetic based sensors [6,7] and excellent reviews are available on such topics [8,9]. Nanocrystalline magnetic alloys such as Ni-Cu, Co-Ni, Fe-Co and Fe-Co-Cu are promising candidates for hyperthermia and microwave applications because their magnetic transition temperatures and microwave absorbance characteristics vary with composition and grain size.…”

Optimization of the magnetic properties of aligned Co nanowires/polymer composites for the fabrication of permanent magnets

“…Such wires can be produced either by electrochemical deposition of metals in uniaxial porous templates such as anodic aluminium oxide (Fert et al 1999), by organo--metallic synthesis (Wetz et al 2007), or by the polyol process (Ung et al 2007;Soumare et al 2008 andSoumare et al 2009). Such wires exhibit specific magnetic properties owing to their large shape anisotropy (Sellmyer et al 2001 andMcGary et al 2005).…”