Synthesis of monodisperse iron-platinum (FePt) nanoparticles by reduction of platinum acetylacetonate and decomposition of iron pentacarbonyl in the presence of oleic acid and oleyl amine stabilizers is reported. The FePt particle composition is readily controlled, and the size is tunable from 3- to 10-nanometer diameter with a standard deviation of less than 5%. These nanoparticles self-assemble into three-dimensional superlattices. Thermal annealing converts the internal particle structure from a chemically disordered face-centered cubic phase to the chemically ordered face-centered tetragonal phase and transforms the nanoparticle superlattices into ferromagnetic nanocrystal assemblies. These assemblies are chemically and mechanically robust and can support high-density magnetization reversal transitions.

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We have used oxygen-plasma-assisted molecular-beam epitaxy (OPA-MBE) to grow CoxTi1−xO2 anatase on SrTiO3(001) for x=∼0.01–0.10, and have measured the structural, compositional, and magnetic properties of the resulting films. Whether epitaxial or polycrystalline, these CoxTi1−xO2 films are ferromagnetic semiconductors at and above room temperature. However, the magnetic and structural properties depend critically on the Co distribution, which varies widely with growth conditions. Co is substitutional in the anatase lattice and in the +2 formal oxidation state in ferromagnetic CoxTi1−xO2. The magnetic properties of OPA-MBE grown material are significantly better than those of analogous pulsed laser deposition-grown material.

The magnetic domain structure and magnetization curves of chemically ordered epitaxial FePt (001) films with perpendicular magnetic anisotropy are discussed. Films were dc magnetron sputtered from a Fe50Pt50 alloy target onto Pt seeded MgO (001) at substrate temperatures of 550 °C. The thickness of the FePt layers was varied between 18 and 170 nm. Specular and grazing incidence x-ray diffraction measurements confirm the presence of the anisotropic, face centered tetragonal (L10) crystal structure. Long range chemical order parameters of up to 0.95 and small mosaic spread, similar to results reported for FePt (001) films grown by molecular beam epitaxy. For film thicknesses ⩾50 nm in-plane and out-of-plane hysteresis measurements indicate large perpendicular magnetic anisotropies and at the same time low (about 10%) perpendicular remanence. Magnetic force microscopy reveals highly interconnected perpendicular stripe domain patterns. From their characteristic widths, which are strongly dependent on the film thickness, a value of the dipolar length D0∼50±5 nm is derived. Assuming an exchange constant of 10−6 erg/cm, this value is consistent with an anisotropy constant K1∼1×108 erg/cc.

We show that under certain conditions, highly Co-enriched TiO2 anatase clusters nucleate on epitaxial TiO2 anatase grown on LaAlO3(001) by oxygen plasma assisted molecular beam epitaxy. In the most extreme cases, virtually all incident Co segregates to the clusters, yielding a nanoscale ferromagnetic phase that is not ferromagnetic in homogeneous films of the same Co concentration. The nucleation of this phase simultaneous with continuous epitaxial film growth must be carefully monitored in order to avoid drawing false conclusions about the film structure.

In low resistance-area product MgO magnetic tunnel junction nanopillars, we observe high integrated power (up to 43nW), narrow linewidth (down to 10MHz), spin transfer induced microwave emission at frequencies up to 14GHz due to precession of the free layer magnetization at room temperature. Although all devices were fabricated on the same wafer, they present bimodal transport and precessional characteristics. The devices in which the narrowest linewidths were observed exhibited low resistance and tunneling magnetoresistance (30%), while maintaining large integrated power.

Previously, ion-beam irradiation has been shown to locally alter the magnetic properties of thin Co/Pt multilayer films. In this work, we have used ion-beam irradiation through a silicon stencil mask having 1-μm-diam holes to pattern a magnetic film. Regularly spaced micrometer-sized regions of magnetically altered material have been produced over areas of a square millimeter in Co/Pt multilayers. These magnetic structures have been observed by magnetic force microscopy. The patterning technique is demonstrated with mask–sample spacing as large as 0.5 mm. In addition, smaller regions of magnetic contrast, down to 100 nm, were created by using two masks with partially overlapping micrometer holes. Such patterned magnetic films are of interest for application in high-density magnetic recording.