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Magnetic nanostructures from block copolymer lithography: Hysteresis, thermal stability, and magnetoresistance

2004; American Physical Society; Volume: 70; Issue: 6 Linguagem: Inglês

10.1103/physrevb.70.064417

1550-235X

Jay Cheng, Won Jung, C. A. Ross,

Theoretical and Computational Physics

A series of two dimensional close-packed $\mathrm{Co}$, $\mathrm{NiFe}$, and $\mathrm{CoFe}∕\mathrm{Cu}∕\mathrm{NiFe}$ magnetic particle arrays, in which the particles have mean diameters of $34\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$, thicknesses of $5--20\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$, and periodicity of $56\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$, were made using a process based on self-assembled polystyrene-$b$-polyferrocenyldimethylsilane block copolymer templates. Interparticle magnetostatic interactions lead to the thermally assisted collective reversal of small groups of particles. The switching field distribution, whose width decreases as the thickness increases, has been modeled as a result of the distribution of particle size, shape, and microstructure. For multilayered particles, interlayer magnetostatic interactions stabilize flux-closed states with antiparallel alignment of the $\mathrm{CoFe}$ and $\mathrm{NiFe}$ layers at remanence. The multilayer particles show a greater thermal stability than single-layer particles, and a magnetoresistance comparable to that of the unpatterned film.