Cluster-Assembled Nanocomposites

Abstract

This chapter focuses on a gas-aggregation technique to prepare magnetic nanoclusters with controllable cluster sizes and size distributions. The review includes current research on nanoclusters, such as uncoated and oxide-coated Fe, Co and Fe clusters and clusters made from alloys, but special emphasis is on highly anisotropic L1 0 -ordered FePt clusters, which are of potential interest for magnetic recording with ultrahigh areal densities of more than 1 Tera bit/in 2 . In particular, we discuss magnetic and structural properties of FePt nanoclusters and thin fi lms. Another approach discussed in the chapter is to create cluster nanocomposites by multilayering with post-deposition annealing. The advantage of this method is that the clusters can be oriented along a desired easy axis. One example is L1 0 -(001) oriented FePt nanocomposite fi lms with a FePt cluster size of about 5 nm.

Prospects for nanoparticle-based permanent magnets

“…The cluster-deposition method using physical vapor deposition processes such as sputtering, thermal evaporation or laser ablation is based on the inert-gas-condensation principle and has been successful in producing both FePt and rare-earth alloy nanoparticles of smaller sizes (2-15 nm) with uniform size distribution and a high degree of atomic ordering [18,[26][27][28][29][30][31][32]. For example, the sputtering of atoms from the solid surface of a desired composition (such as YCo 5 or FePt) in a cooled inert-gas atmosphere (mixture of Ar and He)>10 −2 torr leads to successive collisions of sputtered atoms with the inert gas ions, and thus results in the formation of nanoparticles in the gas phase prior to deposition on substrates kept at room temperature [18,27,30,32].…”

“…For example, the sputtering of atoms from the solid surface of a desired composition (such as YCo 5 or FePt) in a cooled inert-gas atmosphere (mixture of Ar and He)>10 −2 torr leads to successive collisions of sputtered atoms with the inert gas ions, and thus results in the formation of nanoparticles in the gas phase prior to deposition on substrates kept at room temperature [18,27,30,32]. This method produces monodisperse nanoparticles of size d ≤ 10 nm with an rms standard deviation σ/d ≈ 0.15, as shown in the TEM image of YCo 5 nanoparticles ( Figure 2) and corresponding particle size histogram (top inset of Figure 2) [18].…”

“…However, H c can be further improved by producing exchange-decoupled nanoparticles, which are expected to show Stoner-Wohlfarth-type behavior with H c scaling directly with their magnetic anisotropies according to 2K 1 /M s [5,6,16,22,29]. For example, cluster-deposited FePt nanoparticles dispersed in a non-magnetic carbon matrix exhibited a high H c = 29 kOe at room temperature, as shown in Figure 3b, and H c increases further to 40 kOe at 4.2 K [29,32]. The easy axes of these nanoparticles are generally distributed randomly, as revealed by the identical in-plane and out-of-plane hysteresis loops measured in the case of FePt nanoparticles (Figure 3b) and this leads to M r /M s ≈ 0.5.…”

Magnetic entropy changes in nanogranular Fe:Ni61Cu39

“…9 The system produces clusters by combining a dc magnetron sputtering gun using argon and helium as process gases, and the gas-aggregation chamber was held at a temperature of À140 C. The cluster size can be controlled by varying sputtering power, Ar flow rate, He flow rate, and gas-aggregation chamber length. The system also contains two sputtering guns for different matrix materials.…”

Experimental and theoretical studies of hydroxyl-induced magnetism in TiO nanoclusters

“…The Ti oxide clusters are produced using inert-gas condensation in a cluster deposition system that has been described elsewhere 21 [ESI, Fig. S1 †].…”