Interplay between particle anisotropy and exchange interaction in Fe nanoparticle films

The magnetic properties of Fe nanoparticles films were investigated by magnetization measurements and Monte Carlo simulations. The films were produced by femtosecond pulsed laser deposition assisted by irradiation of nanoparticles with a nanosecond UV laser pulse, appropriately delayed, during their flight from the target to the substrate. The films consist of nanoparticles with a disklike shape. The initial magnetization curve exhibits a stepwise behavior, characterized by a reversible plateau followed by rapid irreversible increments. The observed behavior, induced by the peculiar nanoparticle film morphology, is the result of the competition between particle anisotropy, dipole-dipole interactions, and interparticle exchange coupling. This picture is supported by Monte Carlo simulations, satisfactorily reproducing the experimental observations.

Figure 1

Typical AFM image of deposits less than one layer.

Figure 2

(a) Size distribution of the NP in-plane diameter $D$. The inset shows the magnification of the region of big particles. (b) Cumulative distribution of the in-plane diameter.

Figure 3

Initial magnetization curve and hysteresis loop for Fe NP films at RT. The inset shows Δ$M$($H$) behavior of the fsPLD$+$UV NP-assembled Fe samples.

Figure 4

Comparison of initial magnetization curves at RT and 10 K, in Fe NP films.

Figure 5

Initial magnetization curves at RT ($T$ $=$ 0.15 in the model) and 1/30 RT ($T$ $=$ 0.005), as obtained by MC simulations.