Miguel A. Marioni

Methyltrimethoxysilane (MTMS)-based silica–iron oxide superhydrophobic nanocomposites

We report a facile synthesis of superhydrophobic silica-iron oxide nanocomposites via a co-precursor sol-gel process. The choice of the silica precursor (Methyltrimethoxysilane, MTMS) in combination with iron nitrate altered the pore structure dramatically. The influence of iron oxide doping on the structural properties of pristine MTMS aerogel is discussed.

Non-contact bimodal magnetic force microscopy

A bimodal magnetic force microscopy technique optimized for lateral resolution and sensitivity for small magnetic stray fields is discussed. A double phase-locked loop (PLL) system is used to drive a high-quality factor cantilever under vacuum conditions on its first mode and simultaneously on its second mode. The higher-stiffness second mode is used to map the topography. The magnetic force is measured with the higher-sensitivity first oscillation mode.

Engineering the ferromagnetic domain size for optimized imaging of the pinned uncompensated spins in exchange-biased samples by magnetic force microscopy

Magnetic force microscopy (MFM) is able to image and quantify patterns of pinned uncompensated spins (UCS) in exchange-biased samples with high spatial resolution and submonolayer spin sensitivity. However, MFM can only detect magnetic moment distributions with spatial wavelengths within a certain range. Samples with large domains, homogeneous, or divergence-free magnetization fields are not accessible to MFM analysis. In this work we discuss the sample structure constraints placed by the requirement to measure UCS at high spatial resolution, and point out a method to engineer the size of the ferromagnetic domains accordingly.

Bimodal magnetic force microscopy with capacitive tip-sample distance control

A single-passage, bimodal magnetic force microscopy technique optimized for scanning samples with arbitrary topography is discussed. A double phase-locked loop (PLL) system is used to mechanically excite a high quality factor cantilever under vacuum conditions on its first mode and via an oscillatory tip-sample potential on its second mode. The obtained second mode oscillation amplitude is then used as a proxy for the tip-sample distance, and for the control thereof. With appropriate

Halbach Effect at the Nanoscale from Chiral Spin Textures

z

Surface single-molecule dynamics controlled by entropy at low temperatures

-feedback parameters two data sets reflecting the magnetic tip-sample interaction and the sample topography are simultaneously obtained.

Mapping uncompensated spins in exchange-biased systems by high resolution and quantitative magnetic force microscopy

Mallinsons idea that some spin textures in planar magnetic structures could produce an enhancement of the magnetic flux on one side of the plane at the expense of the other gave rise to permanent magnet configurations known as Halbach magnet arrays. Applications range from wiggler magnets in particle accelerators and free electron lasers to motors and magnetic levitation trains, but exploiting Halbach arrays in micro- or nanoscale spintronics devices requires solving the problem of fabrication and field metrology below a 100 μm size. In this work, we show that a Halbach configuration of moments can be obtained over areas as small as 1 μm × 1 μm in sputtered thin films with Néel-type domain walls of unique domain wall chirality, and we measure their stray field at a controlled probe-sample distance of 12.0 ± 0.5 nm. Because here chirality is determined by the interfacial Dyzaloshinkii-Moriya interaction, the field attenuation and amplification is an intrinsic property of this film, allowing for flexibility of design based on an appropriate definition of magnetic domains. Skyrmions (<100 nm wide) illustrate the smallest kind of such structures, for which our measurement of stray magnetic fields and mapping of the spin structure shows they funnel the field toward one specific side of the film given by the sign of the Dyzaloshinkii-Moriya interaction parameter D.

How to measure the local Dzyaloshinskii Moriya Interaction in Skyrmion Thin Film Multilayers

Configuration transitions of individual molecules and atoms on surfaces are traditionally described using an Arrhenius equation with energy barrier and pre-exponential factor (attempt rate) parameters. Characteristic parameters can vary even for identical systems, and pre-exponential factors sometimes differ by orders of magnitude. Using low-temperature scanning tunnelling microscopy (STM) to measure an individual dibutyl sulfide molecule on Au(111), we show that the differences arise when the relative position of tip apex and molecule changes by a fraction of the molecule size. Altering the tip position on that scale modifies the transitions barrier and attempt rate in a highly correlated fashion, which results in a single-molecular enthalpy-entropy compensation. Conversely, appropriately positioning the STM tip allows selecting the operating point on the compensation line and modifying the transition rates. The results highlight the need to consider entropy in transition rates of single molecules, even at low temperatures.

Role of interface coupling inhomogeneity in domain evolution in exchange bias.

Magnetic Force Microscopy is an ideal tool to image magnetic stray fields emanating from surfaces but also from hidden interfaces of magnetic samples. A lateral resolution of 10nm is routinely obtained on flat samples. Tip calibration techniques were developed for a quantitative evaluation of the magnetic surface charge or surface dipole density from the measured MFM signal [1,2].