Evico Magnetics Kerr-Microscope
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.
Via the synchronization of the pulsed LED light source and the camera it is furthermore possible to even reach enhanced ‚pure‘ magneto-optical contrasts (PurePol, PureLong, PureTrans). The pulsed light source can also be used for stroboscopic measurements and time-resolved imaging on the microsecond scale. With this microscope a dipole and a quadrupole magnet can be used to generate magnetic fields in the sample plane (max. 1.3 T) as well as an electromagnet for perpendicular magnetic fields up to 850 mT. Sample motion and drift can be automatically compensated in this setup by a xyz piezo stage.
Sputter deposition machine Z400
The RF sputter deposition system Leybold-Heraeus Z400 allows for the deposition of four different materials from targets in a coplanar arrangement. At the moment a fully automated deposition of layer systems with individual thicknesses from metallic, conducting or semiconducting materials can be performed. The hardware has a base pressure below 10-6 mbar and deposition rates between 1 and 12 nm/min in dependence of the material. The deposition rate can be controlled via the working pressure and the applied power. In addition, there is the option to apply a homogenous magnetic field of 35 mT parallel to the substrate plane during the deposition process.
Field cooling device
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.
Ion bombardment system
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.
Particle transport setups
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.
Vibrating Sample Magnetometer (VSM)
The group’s homebuilt Vibrating Sample Magnetometer (VSM) can be used for measuring magnetization curves of samples with different dimensions (macroscopic and thin film systems) and geometries with the maximum sample size being 20 mm x 20 mm. The VSM measures the integral magnetization of the whole sample, thus, it represents an ideal complementary machine to our other locally confined MOKE based measurement techniques. For the creation of an external magnetic field an electromagnet (Bruker) is used with a maximum field of 2 T at the sample position (default distance of 4 cm between the pole shoes). By rotating the sample holder, it is possible to measure samples with in-plane and out-of-plan magnetization. For investigating special features in the magnetization curve more closely a region of interest can be defined in the measurement software.
Longitudinal and vectorial Kerr magnetometer (L/V-MOKE)
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
on a xy-table in order to automatically raster the sample laterally.
In contrast to the longitudinal Kerr magnetometer, the vectorial Kerr magnetometer has a rotatable sample holder and a quadrupole magnet, which allows an automatized measurement of angular dependent magnetization curves. In addition, an appropriate combination of polarizers and detectors allows to track the magnetization vector (longitudinal and transversal component) in the film plane during magnetization reversal processes.
Surface profilometer (Veeco Dektak 3030)
The surface profilometer Dektak 3030 enables the user to analyze surface structures of 5 nm up to 130 µm height. Therefore, line-scan profiles with a maximum measuring range of 5 mm and a maximum lateral resolution of 40 data points per µm are created using a diamond tipped stylus with a 12.5 µm radius. Adjustable stylus force from 1 mg to 40 mg allows profiling of soft and hard sample surfaces.
Atomic and magnetic force microscope (Nanosurf FlexAFM with C3000 controller)
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
(e.g. AFM + MFM in constant height mode). Here, it can be chosen whether the magnetic scan is performed in a static height above the averaged topography or whether the topography shall be contoured with constant height difference. If required, the software can be extended with additional modules such as advanced spectroscopy or lithography.
Three-dimensional magnetic field characterization
The permanent- and electromagnets installed in the machines of the functional thin films research area, hold a key role in view of the machines’ functionality. Especially the knowledge of the hereby generated three-dimensional magnetic field distribution is crucial for the quantitative modelling of undergoing processes in the respective experiments. Therefore, a setup was developed by analogy to known scanning probe technologies. For measuring the magnetic fields, a Hall sensor with a minimal resolution of 0.5 mT is used. The sensor can be positioned and moved three-dimensionally by using step motors (minimum step size: 20 µm), thus achieving a characterization of the spatial distribution of the examined magnetic field in a definable volume. In addition, the spatial orientation of the Hall sensor can be varied, therefore enabling a consideration of specific boundary conditions. Due to the analogy of the setup to scanning probe microscopy it is also used in several demonstration experiments and practical courses for pupils.