Ordered FePt nanodot arrays with extremely high density have been developed by physical vapor deposition using porous alumina templates as evaporation masks. Nanodot diameter of 18nm and periodicity of 25nm have been achieved, resulting in an areal density exceeding 1×1012dots∕in.2. Rapid thermal annealing converts the disordered fcc to L10 phase, resulting in (001)-oriented FePt nanodot arrays with perpendicular anisotropy and large coercivity, without the need of epitaxy. High anisotropy and coercivity, perpendicular easy axis orientation and extremely high density are desirable features for future magnetic data storage media applications.
Magnetotransport in arrays of monodisperse magnetite nanoparticles has been studied as a function of annealing temperatures. Charge transport mechanisms change from thermally assisted interparticle tunneling to hopping between Fe-sites within the particle as the interparticle spacing is decreased. Despite this difference, magnetoresistance (MR) as a function of field shows a ubiquitous behavior dominated by non-collinear surface spins. All MR as a function of field can be fitted accurately by a Langevin-like function.
A model based on competing exchange interactions is presented for the investigation of nanoparticle magnetization. The ferromagnetic (FM) and antiferromagnetic (AFM) exchange interactions contribute differently at the nanoparticle surface and interior, leading to reduced ferromagnetic order at the surface. This model predicts an unconventional temperature dependence of magnetization and a surface magnetically 'dead layer'. This is confirmed by temperature dependent magnetization and Mössbauer measurements of FePt nanoparticles. The effects are sensitive to particle size and surface terminations.
A diluted magnetic semiconductor (DMS) quantum well is an interesting system for exploring spintronic applications. We calculated the spontaneous magnetization (SM) in a 100-Å Ga1−xMnxAs/Al0.35Ga0.65As quantum well. The Schrodinger equation was described by a 4×4 Luttinger Hamiltonian in the envelope function approximation with the exchange interaction between Mn ions and holes treated in the mean-field approximation. The Schrodinger-Poisson-DMS self-consistency was solved by using the finite element method. We studied how the SM depended on the hole concentration p, the temperature T , the effective Mn concentration x eff , the antiferromagnetic temperature TAF , and the exchange integral βNo. For T = 0 K, x eff = 0.05, TAF = 0.5 K, and βNo = − 1.2 eV, the SM begins to appear at p = 5 × 10 17 cm −3 and saturates around 3 × 10 19 cm −3 . For p = 10 18 cm −3 , the SM disappears around 5 K.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.