2d nanoparticle arrays and 3d nanoparticle crystals

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2D Nanoparticle Arrays and 3D Nanoparticle Crystals. Thin layers (2D) of nanoparticles are formed by evaporating dispersions of nanoparticles on a solid substrate - PowerPoint PPT Presentation

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  • Thin layers (2D) of nanoparticles are formed by evaporating dispersions of nanoparticles on a solid substrateThree-dimensional assemblies are prepared by slowly diffusing a poorly coordinating solvent into the liquid dispersion of nanoparticlesWith Fe nanoparticles the 2D and 3D assemblies have different structural and magnetic behavior2D Nanoparticle Arrays and 3D Nanoparticle Crystals

  • Simulated phase contrastTEM imageLayer Stacking

  • Found for hexagonal close packed arrays of larger Fe nanoparticlesNot seen with nonmagnetic particles

    S. Yamamuro, D. Farrell, and S. A. Majetich, Phys. Rev. B65, 224431 (2002)

    Preference for an Odd Number of Layers

  • Dilute solutions form hexagonal monolayers

    Concentrated solutions form thicker cubic or hexagonal arrays

    BCC structure entropically stabilized for small diameters

    Slower formation increases the coherence length

    2D Array Structure Summary

  • Use very slow precipitation (hours, weeks, months) by diffusion of bad solventCan make 3D array crystals up to 10 microns in sizeParticles dispersed in tolueneEthanolPropanol3D Nanoparticle Arrays

  • For standard surfactants, edge-to-edge interparticle separation 2.5 nm Expect magnetostatic interactions to dominateLearn about interactions from Mr(H), Mrelax(t), MZFC(T)Dipolar Interactions

  • Magnetization with H perpendicular harder to saturate, decays fasterInteractions shape anisotropy in 2D arraysHH=0Field Orientation Mr(H)

  • Dipolar energyper pair of particlesAt T = 10 KVary the Particle Size

  • Larger particles have: slightly faster approach to saturation slower decay in M(t) higher TB and broader M ZFC(T)Particle Size Effects

  • Same batch of 6.7 nm Fe particles with different surfactantsOleic Acid/Oleyl Amine Hexanoic Acid/Hexyl AmineAvg. spacing 2.50.3 nm 1.20.3 nmAt T = 10 KVarying the Particle Spacing

  • Smaller spacing leads to: more gradual saturation slower decay in M(t) a slightly higher Blocking TInterparticle Spacing Effect

  • 3D arrays have: slower approach to saturationhigher TB and broader M ZFC(T) faster decay in M(t) not explained by demagnetization field due to different shape2D and 3D Arrays

  • 5 minutes; x = -0.672 weeks: x = -1.174 weeks: x = -1.89x = -2 Ferromagnetx = -1/2 amorphous magnet (spin glass-like)Remanent magnetization 10 KSmall Lcoh like spin glassLarge Lcoh FMApproach to Saturation

  • Both the strength of dipolar forces and the structural coherence length Lcoh affect the magnetic properties of nanoparticle arrays When Lcoh is long, magnetic relaxation is much faster, suggesting the presence of domain walls within coherent regions Stronger dipolar interactions slow the magnetic relaxation when Lcoh is short, and the arrays are spin glass-likeD. Farrell, Y. Ding, S. A. Majetich, C. Sanchez-Hanke, and C.-C. Kao, J. Appl. Phys. 95, 6636 (2004).D. Farrell, Y. Cheng, Y. Ding, S. Yamamuro, C. Sanchez-Hanke, C.-C. Kao,and S. A. Majetich, J. Magn. Magn. Mater. 282, 1-5 (2004).Magnetics Summary

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