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15 Jul 2004

Volume 96, Issue 2, pp. 951-1278

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Structural and magnetic model of self-assembled FePt nanoparticle arrays

T. Thomson, M. F. Toney, S. Raoux, S. L. Lee, S. Sun, C. B. Murray, and B. D. Terris

J. Appl. Phys. 96, 1197 (2004); http://dx.doi.org/10.1063/1.1759393 (5 pages) | Cited 24 times

Online Publication Date: 30 June 2004

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Chemically ordered, self-assembled FePt nanoparticle arrays with high magnetic anisotropy are considered as a candidate medium for data storage beyond 1 Tbit/in2. We report comprehensive structural and magnetic studies on thin (three-layer) assemblies of polyethylenimine (PEI) and 4 nm Fe58Pt42 nanoparticles using x-ray diffraction, small angle neutron scattering, and magnetometry. We show that prior to annealing FePt nanoparticles in the PEI-FePt assembly consist of a metallic magnetic core surrounded by a weakly magnetic or nonmagnetic shell. High temperature annealing creates the desired L10 chemical ordering and results in high coercivity FePt nanoparticles. However, we find that the high temperatures necessary to establish full chemical ordering leads to particle sintering and agglomeration. Understanding the magnetic and physical properties of these assemblies allows future research directions to be clarified for nanoparticle arrays as data storage media. © 2004 American Institute of Physics.
Show PACS
61.46.-w Structure of nanoscale materials
75.50.Tt Fine-particle systems; nanocrystalline materials
75.30.Gw Magnetic anisotropy
85.70.Li Other magnetic recording and storage devices (including tapes, disks, and drums)
81.40.Gh Other heat and thermomechanical treatments
75.50.Vv High coercivity materials

Size induced variations in structural and magnetic properties of double exchange La0.8Sr0.2MnO3−δ nano-ferromagnet

Sujoy Roy, Igor Dubenko, Dossah D. Edorh, and Naushad Ali

J. Appl. Phys. 96, 1202 (2004); http://dx.doi.org/10.1063/1.1760230 (7 pages) | Cited 36 times

Online Publication Date: 30 June 2004

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A detailed study on the influence of particle size varied from 8 nm to 53 nm on the structural and magnetic properties of La0.8Sr0.2MnO3−δ has been done. The unit cell volume increases and the microstrain in the compound shows peak formation as the particle size decreases. Nano particles of La0.8Sr0.2MnO3−δ exhibit superparamagnetism whose blocking temperature has a nonlinear and logarithmic decreasing tendency as function of particle size and applied magnetic field, respectively. Evidence of formation of a magnetically dead layer at the surface has been found and the ratio of the thickness of the dead layer to the particle size increases exponentially with particle size. The coercivity of the nanoparicles increases manifold as particle size varies from 53 nm to 21 nm. In the single domain region the coercivity exhibits a d−1.125 behavior. The temperature dependence of the saturation magnetization shows strong collective excitation due to the spin wave that varies as Tα with α>αbulk of 3/2. Thus the spin wave does not follow the Bloch law in the case of nano particles of La0.8Sr0.2MnO3−δ. © 2004 American Institute of Physics.
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75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Dd Nonmetallic ferromagnetic materials
75.20.Ck Nonmetals
61.46.-w Structure of nanoscale materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Ds Spin waves

Semiconductor to metal phase transition in the nucleation and growth of VO2 nanoparticles and thin films

J. Y. Suh, R. Lopez, L. C. Feldman, and R. F. Haglund

J. Appl. Phys. 96, 1209 (2004); http://dx.doi.org/10.1063/1.1762995 (5 pages) | Cited 64 times

Online Publication Date: 30 June 2004

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The optical and morphological characteristics of vanadium dioxide nanoparticles and thin films during their nucleation and growth phases have been studied by correlating the temperature and sharpness of the transition with the processing parameters. Thermal annealing results in grain growth and improved crystallinity. Normally, larger crystallites show smaller hysteresis, as there is a greater probability of finding a nucleating defect in the larger volume. But at the same time, this improved crystal perfection, which accompanies the thermal annealing and grain growth, tends to a larger hysteresis, as there are fewer nucleating defects within the volume. We show that the width and shape of the hysteresis cycle are thus determined by the competing effects of crystallinity and grain size.
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81.07.Bc Nanocrystalline materials
81.15.Fg Pulsed laser ablation deposition
61.66.Bi Elemental solids
61.66.Dk Alloys
81.65.Mq Oxidation
81.05.Hd Other semiconductors
71.30.+h Metal-insulator transitions and other electronic transitions
82.60.Nh Thermodynamics of nucleation
81.40.Gh Other heat and thermomechanical treatments
68.55.A- Nucleation and growth

Equilibrium crystal shape of GaAs in nanoscale patterned growth

S. C. Lee and S. R. J. Brueck

J. Appl. Phys. 96, 1214 (2004); http://dx.doi.org/10.1063/1.1757657 (5 pages) | Cited 6 times

Online Publication Date: 30 June 2004

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The equilibrium crystal shape (ECS) of GaAs homoepitaxially grown on a nanoscale SiO2-patterned (001) plane by molecular beam epitaxy is investigated. A GaAs epilayer selectively grown on a nanoscale area bounded by a circular SiO2 mask undergoes faceting, resulting in a pyramidal shape with {110} sidewalls. Growth is slowed or terminated with the generation of these {110} facets even with a continuing supply of Ga atoms. This implies that the pyramidal shape is energetically very stable. Based on experimental results and the Wulff construction, a {110}-type sidewall pyramid is proposed as an ECS of GaAs on (001) in nanoscale patterned growth. © 2004 American Institute of Physics.
Show PACS
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.05.Ea III-V semiconductors
68.55.-a Thin film structure and morphology
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
61.46.-w Structure of nanoscale materials
81.16.Nd Micro- and nanolithography
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