Browsing by Author "Pennycook, Stephen J."

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    The effect of matrix and substrate on the coercivity and blocking temperature of self-assembled Ni nanoparticles
    Abiade, Jeremiah T.; Oh, Sang Ho; Kumar, Dhananjay; Varela, Maria; Pennycook, Stephen J.; Guo, Haizhong; Gupta, Arunava; Sankar, Jagannathan (American Institute of Physics, 2008-10-01)
    We have shown that the magnetic properties of nanoparticles may be tuned from superparamagnetic to ferromagnetic by changing the substrate or thin film matrix in which they are embedded. Nickel nanoparticles were embedded into alumina, titanium nitride, and cerium oxide matrices on both silicon and sapphire substrates via pulsed laser deposition. The laser ablation time on the nickel target was kept constant. Only nickel nanoparticles in cerium oxide showed characteristics of ferromagnetism (room temperature coercivity and remanence). Ni nanoparticles, in either alumina or titanium nitride, possessed blocking temperatures below 200 K. Detailed scanning transmission electron microscopy analysis has been conducted on the samples embedded into cerium oxide on both substrates and related to the magnetic data. (c) 2008 American Institute of Physics.
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    Effect of spacer layer thickness on magnetic interactions in self-assembled single domain iron nanoparticles
    Herndon, Nichole B.; Oh, Sang Ho; Abiade, Jeremiah T.; Pai, Devdas; Sankar, Jag; Pennycook, Stephen J.; Kumar, Dhananjay (American Institute of Physics, 2008-04-01)
    The magnetic characteristics of iron nanoparticles embedded in an alumina thin film matrix have been studied as a function of spacer layer thickness. Alumina as well as iron nanoparticles were deposited in a multilayered geometry using sequential pulsed laser deposition. The role of spacer layer thickness was investigated by making layered thin film composites with three different spacer layer thicknesses (6, 12, and 18 nm) with fixed iron particle size of similar to 13 nm. Intralayer magnetic interactions being the same in each sample, the variation in coercivity and saturation magnetization is attributed to thickness dependent interlayer magnetic interactions of three types: exchange, strong dipolar, and weak dipolar. A thin film composite multilayer structure offers a continuously tunable strength of interparticle dipole-dipole interaction and is thus well suited for studies of the influence of interaction on the magnetic properties of small magnetic particle systems.