Thickness Dependent Perpendicular Magnetic Domain Patterns in Sputtered Epitaxial FePt (001) L10 Films

The present paper discusses the magnetic anisotropy and magnetic domain structure of highly ordered epitaxial FePt(001) films grown on Pt seeded MgO(001) substrates. These films were grown by dc-magnetron sputtering from a Fe50Pt50 alloy target at a substrate temperature of 550°C during deposition. Thicknesses were varied between 15 and 170 nm. The presence of the highly anisotropic face centered tetragonal L10 crystal structure with a maximum long range chemical ordering of 95% and a low degree of misorientations was confirmed by specular and grazing incidence X-ray diffraction measurements. For film thicknesses ≥ 50 nm in-plane and out-of-plane hysteresis measurements indicate large perpendicular magnetic anisotropy and at the same time low remanent magnetisation. Magnetic force microscopy reveals highly interconnected perpendicular stripe domain patterns. From their characteristic width, which is strongly dependent on the film thickness, a value of the dipolar length, D0, of 50 ±5 nm is derived. Assuming an exchange constant of 10-6 erg/cm, this value is consistent with an anisotropy constant Ku ∼ 1.108 erg/cc.

Near-surface nanoscale InAs Hall cross sensitivity to localized magnetic and electric fields

We have measured the room temperature response of nanoscale semiconductor Hall crosses to local applied magnetic fields under various local electric gate conditions using scanning probe microscopy. Near-surface quantum wells of AlSb/InAs/AlSb, located just 5 nm from the heterostructure surface, allow very high sensitivity to localized electric and magnetic fields applied near the device surfaces. The Hall crosses have critical dimensions of 400 and 100 nm, while the mean free path of the carriers is about 160 nm; hence the devices nominally span the transition from diffusive to quasi-ballistic transport. With certain small gate voltages (V(g)) the devices of both sizes are strongly responsive to the local magnetic field at the center of the cross, and the results are well described using finite element modeling. At high V(g), the response to local magnetic fields is greatly distorted by strong electric fields applied near the cross corners. However we observe no change in behavior with the size of the device.

Monodisperse FePt nanoparticles and ferromagnetic FePt nanocrystal superlattices

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.