RESUMEN
Magneto-optical indicator films (MOIFs) are a very useful tool for direct studies of the spatial distribution of magnetic fields and the magnetization processes in magnetic materials and industrial devices such as magnetic sensors, microelectronic components, micro-electromechanical systems (MEMS), and others. The ease of application and the possibility for direct quantitative measurements in combination with a straightforward calibration approach make them an indispensable tool for a wide spectrum of magnetic measurements. The basic sensor parameters of MOIFs, such as a high spatial resolution down to below 1 µm combined with a large spatial imaging range of up to several cm and a wide dynamic range from 10 µT to over 100 mT, also foster their application in various areas of scientific research and industry. The history of MOIF development totals approximately 30 years, and only recently have the underlying physics been completely described and detailed calibration approaches been developed. The present review first summarizes the history of MOIF development and applications and then presents the recent advances in MOIF measurement techniques, including the theoretical developments and traceable calibration methods. The latter make MOIFs a quantitative tool capable of measuring the complete vectorial value of a stray field. Furthermore, various scientific and industrial application areas of MOIFs are described in detail.
RESUMEN
We experimentally study the thermoelectrical signature of individual skyrmions in chiral Pt/Co/Ru multilayers. Using a combination of controlled nucleation, single skyrmion annihilation, and magnetic field dependent measurements the thermoelectric signature of individual skyrmions is characterized. The observed signature is explained by the anomalous Nernst effect of the skyrmion's spin structure. Possible topological contributions to the observed thermoelectrical signature are discussed. Such thermoelectrical characterization allows for noninvasive detection and counting of skyrmions and enables fundamental studies of topological thermoelectric effects on the nanoscale.
RESUMEN
A new metrological large range magnetic force microscope (Met. LR-MFM) has been developed. In its design, the scanner motion is measured by using three laser interferometers along the x, y, and z axes. Thus, the scanner position and the lift height of the MFM can be accurately and traceably determined with subnanometer accuracy, allowing accurate and traceable MFM measurements. The Met. LR-MFM has a measurement range of 25 mm × 25 mm × 5 mm, larger than conventional MFMs by almost three orders of magnitude. It is capable of measuring samples from the nanoscale to the macroscale, and thus, it has the potential to bridge different magnetic field measurement tools having different spatially resolved scales. Three different measurement strategies referred to as Topo&MFM, MFMXY, and MFMZ have been developed. The Topo&MFM is designed for measuring topography and MFM phase images, similar to conventional MFMs. The MFMXY differs from the Topo&MFM as it does not measure the topography profile of surfaces at the second and successive lines, thus reducing tip wear and saving measurement time. The MFMZ allows the imaging of the stray field in the xz- or yz-planes. A number of measurement examples on a multilayered thin film reference sample made of [Co(0.4 nm)/Pt(0.9 nm)]100 and on a patterned magnetic multilayer [Co(0.4 nm)/Pt(0.9 nm)]10 with stripes with a 9.9 µm line width and 20 µm periodicity are demonstrated, indicating excellent measurement performance.
RESUMEN
The magnetic properties of monodisperse FeO-Fe3O4 nanoparticles with different mean sizes and volume fractions of FeO synthesized via decomposition of iron oleate were correlated to their crystallographic and phase compositional features by exploiting high resolution transmission electron microscopy, X-ray diffraction, Mössbauer spectroscopy and field and zero field cooled magnetization measurements. A model describing the phase transformation from a pure Fe3O4 phase to a mixture of Fe3O4, FeO and interfacial FeO-Fe3O4 phases as the particle size increases was established. The reduced magnetic moment in FeO-Fe3O4 nanoparticles was attributed to the presence of differently oriented Fe3O4 crystalline domains in the outer layers and paramagnetic FeO phase. The exchange bias energy, dominating magnetization reversal mechanism and superparamagnetic blocking temperature in FeO-Fe3O4 nanoparticles depend strongly on the relative volume fractions of FeO and the interfacial phase.
RESUMEN
The quantitative measurement of the magnetization of individual magnetic nanoparticles (MNPs) using magnetic force microscopy (MFM) is described. Quantitative measurement is realized by calibration of the MFM signal using an MNP reference sample with traceably determined magnetization. A resolution of the magnetic moment of the order of 10(-18) A m(2) under ambient conditions is demonstrated, which is presently limited by the tip's magnetic moment and the noise level of the instrument. The calibration scheme can be applied to practically any magnetic force microscope and tip, thus allowing a wide range of future applications, for example in nanomagnetism and biotechnology.
