Machines

With this high resolution optical microscope (Objectives up to 100 x) magnetic domains and magnetization processes can be visualized by the magneto-optical Kerr effect. Measuring a magnetic hysteresis loop (magnetometry) can be obtained via the grey value of each difference image in the loop. The different magnetization components of a sample are measured and displayed depending on the choice of the light incidence.

For initialising or post modification of the exchange bias (EB) effect the respective magnetic thin film systems are exhibited to a field cooling procedure. For this purpose, a field cooling device is used, where the samples are stored in a vacuum chamber (base pressure: 10^-6 mbar) and heated to an adjustable temperature (between 100 °C and 350 °C) i.e. the chosen temperature is typically above the temperature needed to induce thermal activation processes within the respective EB layer system. The heating is carried out in a homogenous magnetic field with a strength of 80 mT parallel to the film plane, so that the direction of the magnetic field can, e.g. determine the direction of the induced unidirectional anisotropy in an EB system. The samples are heated at the given temperature for a set time, which is by default 60 min, and subsequently cooled down to room temperature, still with the magnetic field applied. In case of an EB system, the state of the antiferromagnetic layer is set during this process. For specific purposes, the cooling rate given in K/min can be almost arbitrarily set.

The home-built ion bombardment system ‘ISA’ allows for the application of accelerated Helium ions in particular for the modification of magnetic thin film systems. The continuous bombardment with a square shaped ion beam with an area of 2x2 mm² during sample stage motion makes it possible to homogeneously bombard an area of 80 mm x 100 mm and, thus, to magnetically pattern almost any sample. The ion energy can be tuned from 5 keV to 30 keV, while the tunable Penning type ion source enables to set the ion beam current to a value between 0.01 µA and 3 µA. Hence, the ion fluency can be set between 10¹³ ions/cm² and 10¹⁷ ions/cm². Besides the bombardment of one position, the automatized movement of the sample underneath the beam allows for the bombardment of areas or of stripes with fluency gradients. The optionalapplication of a homogenous magnetic field of up to 80 mT allows for the tailoring of magnetic domain configurations, e.g. in exchange biased thin film systems.

The particle transport setups are home-built devices used in the magnetic actuation and observation of micron- and nano-sized objects. They are made of three main elements: camera, optical path and electromagnets for the creation of magnetic fields that are needed for initializing the desired dynamics. For each main element there are multiple parts that can be exchanged to fit different observations orexperiments. There are three cameras available, two of which are high speed (Mikrotron, Optronis) cameras while one is used for fluorescent particles (pco.pixelfly). For each of these cameras, a fitting optical path, together with multiple objective magnifications (20 times to 100 times) can be implemented. There are also multiple configurations of electromagnets to adjust for gradient fields and homogeneous fields that can produce flux densities of up to a few tens of mT.

With the longitudinal Kerr magnetometer it is possible to measure magnetization curves of magnetic thin films with in-plane magnetization via the magneto-optic Kerr effect.

For that, a Laser as a monochromatic light source, a dipolar electromagnet, an optical system based on lenses and polarizers as well as a photodiode are combined. The used light-source has a spot size of approximately 100 µm and the sample holder is placed

Topographic structures or magnetic patterns can be examined with the Nanosurf FlexAFM, which exhibits a digital resolution in the (sub)picometer regime (XY: 6 pm, Z: 0.6 pm). The special flexure-based electromagnetically actuated XY-scanner (max. scan range 100 µm x 100 µm) combined with the piezo-driven Z-scanner (max. scan range 10 µm) allows the user to analyze relatively large sample areas with comparably high scan speeds of maximum 60 ms per line. Currently used operating modes are static and dynamic force (AFM) as well as phase contrast for measuring the magnetic stray fields emerging from a sample