Variation of intrinsic magnetic parameters of single domain CoN interstitial nitrides synthesized via hexa-ammine cobalt nitrate route

doi:10.1016/j.matchemphys.2012.03.005

Materials Chemistry and Physics

Volume 134, Issue 1, 15 May 2012, Pages 377-381

https://doi.org/10.1016/j.matchemphys.2012.03.005 Get rights and content

Abstract

We report the variation of Curie temperature (T_c) and coercivity (H_c) of the single domain Co single bond N interstitial materials synthesized via nitridation of the hexa-ammine Cobalt(III) nitrate complex at 673 K. CoN materials crystallize in the fcc cubic structure with unit cell parameter, a = 3.552 Å. The X-ray diffraction (XRD) peaks are broader indicating the materials to be nano-structured with crystallite sizes of 5–14 nm. The scanning electron microscopy (SEM) and transmission electron microscopy (TEM) studies confirm the nanocrystalline nature of the materials. TEM images show chain-like clusters indicating dipolar interactions between the particles. Magnetic studies focus on the existence of giant magnetic Co atoms in the Co single bond N lattice that are not influenced by the thermal relaxation. The values of the H_c could be tuned with the dimension of the particles. The values of T_c of the nitride materials are masked by the onset of the ferromagnetic to superparamagnetic transition at higher temperatures. Thermomagnetic studies show an increasing trend in the Curie temperature, T_c, with decrease in particle dimension. This result has been explained qualitatively on the basis of ferromagnetic to superparamagnetic transition and finite size scaling effects.

Highlights

► Variation of intrinsic magnetic parameters of Co single bond N. ► Synthesis by hexa-ammine cobalt complex route. ► Tuning of coercivity by variation of size.

Introduction

Researches on the drug delivery and bio-sensing have experienced rapid growth and a tremendous amount of innovation and development. There has been an increasing interest to use magnetic particles in biomedical applications [1], [2], [3]. Magnetic particles are suitable for use in biosensor applications, since their magnetic properties allow relatively easy detection. A single bond covalent immobilization of aminated DNA probes on magnetic particles has been developed [2]. The technique is suitable for selective molecular hybridization of traces of DNA samples. Due to the extremely sensitive procedure for purification/detection DNA/RNA from biological samples, magnetic nanoparticles containing DNA probe is required. Also, it has been well known that magnetic targeting of drugs and genes requires suitable alternative materials. The phenomenon of superparamagnetism has given the greatest challenge to the magnetic materials to be used for its practical applications. The intrinsic magnetic properties, e.g. saturation magnetization (M_s), Curie temperature (T_c), magnetic hyperfine field (ΔH_f) and coercivity (H_c), are found to change with the reduction of the dimension of the magnetic particles [4], [5], [6], [7], [8]. An additional problem is associated with the chemical stability of the particles [9]. However, the advanced processes of the surface coatings with a blend of Al have resulted highly passivated surfaces having lower corrosion properties [10]. Metals or alloy particles possess poor magnetocrystalline anisotropy and chemical stability [11]. Recently, attempts have been made in the structure–property correlation of various interstitial Fe, Ni, V and Mo nitride systems and their substituted products [6], [12], [13], [14], [15], [16], [17], [18], [19], [20], [21]. It is interesting to note that insertion of N₂ (g) in the metallic lattice develops corrosion resistance at the ambient conditions. Therefore, syntheses of smaller ferromagnetic iron-nitride particles, e.g. Fe₁₆N₂, Fe₃N, Fe₄N, etc., and their substituted products have been a subject of extensive research [6], [12], [22], [23], [24]. In this regard, research on the productions of single-domain nitrides in order to explore their anisotropic behavior with controlled coercivities, surface magnetic structures, surface disorder and its effect on magnetic relaxation, surface reconstruction, surface spin disorder arising out of the reduced co-ordinations, varieties of the oxidation states and broken exchange bonds between the surface spins, etc., merits further investigations. The control of the particle sizes and their distribution so as to tune the values of the Curie temperatures, saturation magnetization and coercivities for the Co single bond N system, have been presented in this investigation. We are successful in changing the coercivities of the CoN materials having higher values of the saturation magnetization, i.e. 123.1 emu g⁻¹, so that it may assume an ideal soft magnetic system. Such CoN systems will be useful for magnetic materials in biosensor and bioelectronic applications because their properties could be tuned by N-content in the lattice and particle sizes.

Section snippets

Synthetic strategy for CoN materials

The Co single bond N materials can be prepared by simultaneous thermal decomposition and nitridation of the Cobalt(III) hexa-ammine nitrate complex, [Co(NH₃)₆](NO₃)₃. The production of various amine products by the related synthetic strategy has been established in the literature [25], [26]. The material is synthesized by addition of 100 ml of concentrated NH₃ solution (Merck, India) into 1 g of [Co(NH₃)₆](NO₃)₃ (99%, Merck, Germany) in the presence of H₂O₂ at 298 K. H₂O₂ being oxidizing agent, helps in the

Precursor characterization

We tried to identify the hexa-ammine Co(III) nitrate complex by differential thermal analysis technique and tried to match the DTA profiles with the literature reported values [26]. The behavior of [Co(NH₃)₆](NO₃)₃ in O₂ atmosphere by differential thermal analysis (DTA) has been exploited. The DTA curves show chemical reactions corresponding to the values of the peak positions found at 179.8, 208.6 and 264.3 °C. These values agree well with the reported values [26]. The first two peaks have been

Conclusions

We could successfully synthesize ultrafine Co single bond N nitride particles by employing the temperature program reactions using Co-hexa-ammine complex precursor. On nitridation of the precursor complex at various temperatures, evolution of CoN phase occurs via Co₂N, and Co₃N phases as examined by XRD. The nano-crystalline nature has been confirmed by XRD line broadening, SEM and TEM measurements. TEM images show chain like clusters of the nano-particles. Magnetic studies confirm the presence of

Acknowledgements

We would like to acknowledge D.S.T. and CSIR New Delhi for the financial support during this investigation.

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Variation of intrinsic magnetic parameters of single domain CoN interstitial nitrides synthesized via hexa-ammine cobalt nitrate route

Abstract

Highlights

Introduction

Section snippets

Synthetic strategy for CoN materials

Precursor characterization

Conclusions

Acknowledgements

Biosens. Bioelectron.

Biosens. Bioelectron.

Biosens. Bioelectron.

J. Magn. Magn. Mater.

J. Magn. Magn. Mater.

J. Magn. Magn. Mater.

J. Magn. Magn. Mater.

Mater. Res. Bull.

Mater. Res. Bull.

Mater. Res. Bull.

Phys. Rev. Lett.

Phys. Rev. B

J. Appl. Phys.

J. Magn. Magn. Mater.

IEEE Trans. Magn.

J. Appl. Phys.