Ildico L. Guhr

Arrays of magnetic nanoindentations with perpendicular anisotropy

The authors report an approach to the fabrication of periodic magnetic patterns using spherical indentations. These troughs are shaped by an imprint technique, employing a self-assembled monolayer of particles. Well-defined structures with perpendicular magnetic anisotropy are obtained by deposition of Co∕Pd multilayer films onto the topographic array. The structures formed in the indentations can be magnetically exchange decoupled from their neighbors depending critically on their specific shape. The presented concept leads to a realization of a magnetic nanostructure medium, which offers advances in achieving high pattern densities combining a low cost nanoimprint approach with material functionalization.

Control of magnetic anisotropy and magnetic patterning of perpendicular Co∕Pt multilayers by laser irradiation

We report an approach to altering the magnetic properties of (111) textured Co∕Pt multilayer films grown on sapphire (0001) substrates in a controlled way using single-pulse laser irradiation. The as-grown films reveal a strong perpendicular magnetic anisotropy induced by interfacial anisotropy. We show that laser irradiation can chemically mix the multilayer structure particularly at the interfaces, hence reducing the perpendicular magnetic anisotropy and coercivity in a controlled manner depending on laser fluence. As a result, perpendicular films can also be magnetically patterned into hard and soft magnetic regions using a regular two-dimensional lattice of polystyrene particles acting as an array of microlenses.

Magnetization reversal in exchange biased nanocap arrays

Arrays of self-assembled polystyrene spheres with various particle sizes have been used as a substrate to study the exchange bias effect along the out-of-plane direction of Pt/Co multilayers capped with IrMn layers. The evolution of the reversal process of the resulting magnetic nanocaps was investigated by magnetic force microscopy (MFM) and magnetic transmission x-ray microscopy (M-TXM). Tip?sample interaction-induced irreversible and reversible switching events have been observed during multiple scanning cycles in MFM imaging which are ascribed to the so-called training effect. During M-TXM imaging a drastic change in morphology has been found due to the x-ray exposure, leading to the formation of much larger spherical particles. Interestingly, these merged particles reveal again an exchange coupled single-domain magnetic cap with magnetic behaviour similar to magnetic films deposited directly on spheres of similar size.

Structural and magnetic properties of CrPt3(111) films grown on WSe2(0001)

We report on the growth-induced properties of 30 A thick CrPt3(111) deposits on surfaces of WSe2(0001) with a van der Waals interaction. Assemblies of (111)-oriented fcc grains are obtained with average lateral sizes ranging from 5 to 15 nm for growth temperatures increasing from 50 °C to 550 °C. The grains develop a partial L12-type chemical long-range order starting at a deposition temperature as low as 50 °C, much lower than reported for films grown on other suitable substrate surfaces. An ordering parameter of about 0.3 was found over a wide temperature range between 200 °C and 550 °C, for a deposition rate of 0.1 A/s. Lowering the deposition rate by a factor of 5 results in a higher ordering parameter of about 0.4. Above 400 °C, ordering is accompanied by a pronounced segregation of Se atoms toward the free surface, forming a (4×4) superstructure. All samples exhibit superparamagnetic behavior with blocking temperatures that scale with the activation volume of the ferrimagnetic grains. This work show...