Details of synthesis and structural characterization of highly crystalline iron oxide nanoparticles are presented together with results on the magnetic investigation as a function of the temperature and applied field. Monodisperse Fe nanoparticles were prepared by thermal decomposition of iron pentacarbonyl in the presence of oleic acid. These iron nanoparticles were readily oxidized on exposure to air. The resulting nanocrystals have been identified as inverse spinels, being $\gamma \text{−}{\mathrm{Fe}}_2{\mathrm{O}}_3$ the dominant phase of the small $5\text{−}\mathrm{nm}$ iron oxide nanocrystals, whereas the proportion of the ${\mathrm{Fe}}_3{\mathrm{O}}_4$ component gradually increases on increasing the particle size. The small particles volume resulted in finite-size effects, for instance, the magnetization deviates from the $T^{3∕2}$ Bloch’s law. At the same time, high field irreversibility and shifted hysteresis loops after field-cooled processes have been detected, and attributed to a low-temperature surface spin-glass layer. Moreover, there is a critical diameter below which the surface spin-glass behavior and exchange bias effect abruptly disappear.

Structurally gradient layered $\text{A}1/\text{L}{1}_0$ films are obtained by heat treatment of magnetron sputter deposited FePt(20 nm)/CoPt($x$ nm) bilayers where $x=0–120\text{nm}$ . The magnetic properties can be tuned by adjustment of the layer thicknesses and taking advantage of the different heat-treatment temperatures required for the ordering of the $\text{L}{1}_0$ phase between FePt and CoPt.

Thin film libraries of Fe-Co-V were fabricated by combinatorial sputtering to study magnetic and structural properties over wide ranges of composition and thickness by high-throughput methods: synchrotron X-ray diffraction, magnetometry, composition, and thickness were measured across the Fe-Co-V libraries. In-plane magnetic hysteresis loops were shown to have a coercive field of 23.9 kA m^–1 (300 G) and magnetization of 1000 kA m^–1. The out-of-plane direction revealed enhanced coercive fields of 207 kA m^–1 (2.6 kG) which was attributed to the shape anisotropy of column grains observed with electron microscopy. Angular dependence of the switching field showed that the magnetization reversal mechanism is governed by 180° domain wall pinning. In the thickness-dependent combinatorial study, co-sputtered composition spreads had a thickness ranging from 50 to 500 nm and (Fe₇₀Co₃₀)_100-xV_x compositions of x = 2–80. Comparison of high-throughput magneto-optical Kerr effect and traditional vibrating sample magnetometer measurements show agreement of trends in coercive fields across large composition and thickness regions.

Hard-FePt(L1₀)/graded-FePt(L1₀ to A1) exchange spring composite media with perpendicular magnetic anisotropy have been studied. Changing the deposition temperature affects the structural transformation of FePt from cubic phase A1, which is magnetically soft, to the tetragonal phase L1₀, which is magnetically hard. Using this mechanism we were able to fabricate hard/graded composite films. Magnetic measurements revealed a significant reduction of the composite films’ switching fields in comparison with those of the single hard layer.