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15 May 2003

Volume 93, Issue 10, pp. 5855-8792

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CoPt hard magnetic nanoparticle films synthesized by high temperature chemical reduction

Y. Sui, L. Yue, R. Skomski, X. Z. Li, J. Zhou, and D. J. Sellmyer

J. Appl. Phys. 93, 7571 (2003); http://dx.doi.org/10.1063/1.1544501 (3 pages) | Cited 26 times

Online Publication Date: 9 May 2003

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The synthesis of hard-magnetic CoPt nanoparticle films by hydrogen reduction of Co nitride and Pt chloride mixture is reported. Thin porous alumina films are adopted as the carrier of the initial aqueous solution and of the final reducing products of CoPt nanoparticles. It is found that chemical ordering of L10–CoPt occurs above 400 °C. Partial phase transformation occurs in the alumina substrate when the treatment temperature is higher than 600 °C. The film coercivity increases with increasing annealing temperature and reaches a maximum value of 24.2 kOe when the reduction is carried out at 700 °C for 2 h. © 2003 American Institute of Physics.
Show PACS
75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Vv High coercivity materials
81.07.Bc Nanocrystalline materials
81.16.Be Chemical synthesis methods
75.70.Ak Magnetic properties of monolayers and thin films
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Cc Other ferromagnetic metals and alloys

Towards direct synthesis of fct-FePt nanoparticles by chemical route

B. Jeyadevan, A. Hobo, K. Urakawa, C. N. Chinnasamy, K. Shinoda, and K. Tohji

J. Appl. Phys. 93, 7574 (2003); http://dx.doi.org/10.1063/1.1558258 (3 pages) | Cited 49 times

Online Publication Date: 9 May 2003

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The possibility for direct synthesis of fct-FePt nanoparticles of the order of 3–4 nm in diameter through the coreduction of iron and platinum ions in a polyol has been explored. We have succeeded in the synthesis of face-centered cubic structured 3–4 nm diameter FePt particles whose composition was very close to Fe50Pt50. The Fe:Pt ratio was influenced little by the molar ratios of Fe and Pt acetylacetonate dissolved in ethylene glycol. However, depending on the polyol/Pt ratio, the as-prepared samples were either superparamagnetic or ferromagnetic. The transition temperature (Tt) and magnetic properties of the as-prepared FePt were very sensitive to the reaction conditions, and the Tt varied between 593 and 893 K and the particles were ferromagnetic. The as-prepared FePt under the optimum condition had a Tt as low as 593 K and Hc as high as 1.11 kOe at an applied field of 1 T at room temperature. Furthermore, when the as-prepared FePt nanoparticles with Tt around 593 K were annealed at 673 K in H2/N2 atmosphere for an hour they transformed to the ordered fct (L10) structure with coercivity as high as 4.2 kOe at 300 K. This confirmed the lowering of Tt by the manipulation of the reaction condition alone. © 2003 American Institute of Physics.
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81.16.Be Chemical synthesis methods
75.50.Tt Fine-particle systems; nanocrystalline materials
61.46.-w Structure of nanoscale materials
81.07.Wx Nanopowders
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
81.05.Cy Elemental semiconductors
61.66.Dk Alloys
81.05.Bx Metals, semimetals, and alloys
81.40.Rs Electrical and magnetic properties related to treatment conditions
81.40.Gh Other heat and thermomechanical treatments
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.40.-s Critical-point effects, specific heats, short-range order
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Bb Fe and its alloys

Structure and magnetic properties of in-plane oriented FePt–Ag nanocomposites

Y. Z. Zhou, J. S. Chen, G. M. Chow, and J. P. Wang

J. Appl. Phys. 93, 7577 (2003); http://dx.doi.org/10.1063/1.1558260 (3 pages) | Cited 10 times

Online Publication Date: 9 May 2003

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By cosputtering Ag with FePt on a Cr90Ru10 underlayer, the film texture and magnetic easy axis were successfully changed from the perpendicular to the longitudinal direction. The crystallographic structure and magnetic properties of Ag-doped FePt thin films were investigated. Doping of Ag in FePt films led to greater in-plane coercivity and smaller magnetic grain size. The in-plane coercivity of the nanocomposite films varied from 0.8 to 6.5 kOe, depending on the Ag content. With an increase in Ag content, the FePt grain size became smaller, and the magnetic reversal mechanism approached the nucleation mode. These results suggest a practical way by which to fabricate L10 FePt thin films with longitudinal anisotropy using a nanocomposite approach. © 2003 American Institute of Physics.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
68.55.-a Thin film structure and morphology
81.15.Cd Deposition by sputtering
75.50.Tt Fine-particle systems; nanocrystalline materials
75.30.Gw Magnetic anisotropy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.60.Jk Magnetization reversal mechanisms
75.50.Bb Fe and its alloys

Ordering process of sputtered FePt films

Y. K. Takahashi, M. Ohnuma, and K. Hono

J. Appl. Phys. 93, 7580 (2003); http://dx.doi.org/10.1063/1.1538174 (3 pages) | Cited 19 times

Online Publication Date: 9 May 2003

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We have investigated the in situ ordering process of sputtered FePt thin films deposited on heated substrates at 300 °C with different thicknesses. The films thinner than 50 nm were composed of nanograins (∼5 nm) of disordered FePt phase. Recrystallization occured when films were grown thicker than 100 nm, and transformation twins were observed in recrystallized grains, in which ordering to the L10 structure was confirmed. © 2003 American Institute of Physics.
Show PACS
68.55.-a Thin film structure and morphology
61.46.-w Structure of nanoscale materials
81.15.Cd Deposition by sputtering
81.07.Bc Nanocrystalline materials
75.70.Ak Magnetic properties of monolayers and thin films
75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Bb Fe and its alloys

Polyol-process-derived CoPt nanoparticles: Structural and magnetic properties

C. N. Chinnasamy, B. Jeyadevan, K. Shinoda, and K. Tohji

J. Appl. Phys. 93, 7583 (2003); http://dx.doi.org/10.1063/1.1558259 (3 pages) | Cited 28 times

Online Publication Date: 9 May 2003

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We report the synthesis and magnetic properties of CoPt nanoparticles by using the polyol process. Since the reduction potential of Pt is more positive than Co, Pt is easily reduced compared to Co. Hence, CoPt nanoparticles were realized by coreducing cobalt and platinum acetylacetonate in the presence of an appropriate amount of OH ions in trimethylene glycol. X-ray diffraction and transmission electron microscopy studies showed that the as-synthesized CoPt nanoparticles had fcc structure and about 5 nm in diameter. Composition analysis reveals that the as-synthesized particles are almost equiatomic Co50Pt50. Magnetic characterization revealed that these nanoparticles are ferromagnetic at room temperature, and that the magnetization and coercivity values were 8 emu/g and 380 Oe, respectively. Differential scanning calorimetry studies showed that the ordering temperature of the as-synthesized particles was only 550 °C (peak temperature), against 825 °C of the bulk. Annealing the CoPt nanoparticles above 550 °C induced ordering with enhanced magnetic properties. © 2003 American Institute of Physics.
Show PACS
75.50.Tt Fine-particle systems; nanocrystalline materials
81.07.Bc Nanocrystalline materials
61.46.-w Structure of nanoscale materials
75.50.Cc Other ferromagnetic metals and alloys
81.16.Be Chemical synthesis methods
75.50.Ss Magnetic recording materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
81.40.Rs Electrical and magnetic properties related to treatment conditions

Phase transition, thermodynamic properties, and microstructure of Fe–Pt based alloys

P. D. Thang, E. Brück, K. H. J. Buschow, and F. R. de Boer

J. Appl. Phys. 93, 7586 (2003); http://dx.doi.org/10.1063/1.1538175 (3 pages)

Online Publication Date: 9 May 2003

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The kinetics of the face-centered-cubic to face-centered-tetragonal phase transition in Fe59.7Pt39.8Nb0.5 and Fe59.85Pt39.9Al0.25 alloys was studied using data of differential-scanning calorimetry in conjunction with the Johnson–Mehl–Avrami model. The results show that in the Nb-containing alloy, the transition includes both nucleation and growth processes. In the Al-containing alloy, the growth process is dominant during the transition. These differences can be related to the microstructure of the studied alloys. © 2003 American Institute of Physics.
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64.70.K- Solid-solid transitions
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
64.60.Q- Nucleation
65.40.G- Other thermodynamical quantities
75.50.Bb Fe and its alloys

Chemical synthesis of narrowly dispersed SmCo5 nanoparticles

Hongwei Gu, Bing Xu, Jiancun Rao, R. K. Zheng, X. X. Zhang, K. K. Fung, and Catherine Y. C. Wong

J. Appl. Phys. 93, 7589 (2003); http://dx.doi.org/10.1063/1.1537697 (3 pages) | Cited 34 times

Online Publication Date: 9 May 2003

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In this article we report a chemical synthetic means for generating a high Ku magnetic material—narrowly dispersed nanoparticles of SmCo5. Using Co2(CO)8 and Sm(acac)3 as the precursors under air-free conditions, we produced SmCo5 nanoparticles according to the procedure reported by Sun et al. [Science 287, 1981 (2000)] but with some modifications. The nanoparticles, with diameters of 6–8 nm, have a SmCo5 composition, as indicated by transmission electron microscopy, electron diffraction, and x-ray photoelectron spectroscopy. The magnetization measurement of the nanoparticles, exhibits superparamagnetism, which is blocked for temperatures below ∼110 K, suggesting Ku to be ∼2.1×106 erg/cm3 for the as-prepared particles. © 2003 American Institute of Physics.
Show PACS
81.16.Be Chemical synthesis methods
61.46.-w Structure of nanoscale materials
75.50.Tt Fine-particle systems; nanocrystalline materials
81.07.Wx Nanopowders
81.05.Bx Metals, semimetals, and alloys
81.05.Cy Elemental semiconductors
75.30.Gw Magnetic anisotropy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

High anisotropy Sm–Co nanoparticles: Preparation by cluster gun technique and their magnetic properties

S. Stoyanov, V. Skumryev, Y. Zhang, Y. Huang, G. Hadjipanayis, and J. Nogués

J. Appl. Phys. 93, 7592 (2003); http://dx.doi.org/10.1063/1.1544503 (3 pages) | Cited 19 times

Online Publication Date: 9 May 2003

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Sm–Co nanoparticles with 7 nm mean diameter have been obtained by gas condensation in a cluster gun. By absorbing light from quartz halogen bulbs, the nanoparticles are annealed during their flight from the cluster gun to the substrate and are embedded in a carbon matrix by cosputtering. This in situ annealing results in nanoparticles with moderate coercivity. The moderate coercivity and its strong temperature dependence imply a strong effect of the thermal fluctuations, which can be partly overcome by embedding the nanoparticles in an antiferromagnetic matrix (CoO) rather than in a paramagnetic C. © 2003 American Institute of Physics.
Show PACS
75.50.Tt Fine-particle systems; nanocrystalline materials
75.75.-c Magnetic properties of nanostructures
75.50.Ww Permanent magnets
75.30.Gw Magnetic anisotropy
75.50.Cc Other ferromagnetic metals and alloys
61.46.-w Structure of nanoscale materials
81.07.Wx Nanopowders
81.07.Bc Nanocrystalline materials
81.40.Gh Other heat and thermomechanical treatments
81.40.Rs Electrical and magnetic properties related to treatment conditions
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Vv High coercivity materials
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