Jeon Kim

Monolayer CoPt magnetic nanoparticle array using multiple thin film depositions

A monolayer of L10 CoPt nanoparticles was prepared on a polyimide film by depositing Co–Pt and annealing the resulting film stack at 650–800°C. To obtain well-separated magnetic nanoparticles avoiding substantial coarsening often seen on annealing of thicker films, a multiple deposition of thinner Co–Pt alloy films with intentionally increased Co composition was employed. The multiple depositions relying on heterogeneous nucleation on the preexisting CoPt nanoparticles allowed the average particle size to increase from 4to7nm. The monolayer of 7nm sized CoPt nanoparticles exhibited a coercivity of 9.8kOe with a remanence ratio of 0.72.

Spatially periodic magnetic structure produced by femtosecond laser-interference crystallization of amorphous Co2MnSi thin film

Femtosecond laser-interference crystallization (FLIC) was used to form a spatially periodic magnetic structure by selectively crystallizing a paramagnetic amorphous Co2MnSi thin film. Regularly spaced alternating lines of polycrystalline and microcrystalline regions with a periodicity of 2μm were produced by FLIC. The crystalline region composed of ∼100-nm-sized grains contained a nonequilibrium ferromagnetic phase intermixed with β-Mn. The areas between the crystallized lines also received sufficient energy, crystallizing into a microcrystalline state with its grain size ranging from 1 to 5 nm. The magnetic force microscopy of the samples clearly revealed the one-dimensional periodic magnetic domains resulting from the modulated microstructure.