Research in the AG Wende focuses on magnetic nanostructures in the form of thin film and nanoparticle samples. We investigate their electronic and geometrical structure as well as their magnetic properties, with the key techniques being X-ray absorption and Mössbauer spectroscopy. For further sample characterization we use VSM and SQUID magnetometry, X-ray diffraction, as well as electron diffraction, photo- and Auger-electron spectrosopy.

XAS, XMCD, XLD, NEXASF, EXAFS X-ray absorption spectroscopy

The absorption of X-rays in the range of the electron binding energies provides element-selective methods to study geometrical and electronic structure as well as magnetic properties. Due to the element-selectivity the contribution of each constituting element in modern magnetic materials and heterostructures can be separated from the overall behavior of the entire samples. In the near edge range, the measured absorption spectra provide the near edge X-ray absorption fine structure (NEXAFS) and X-ray magnetic circular dichroism (XMCD) whereas from the extended energy range the extended X-ray absorption fine structure (EXAFS) and magnetic EXAFS (MEXAFS) are obtained.

Additionally, we also utilize scattering methods, such as nuclear resonant inelastic X-ray scattering (NRIXS) in order to probe local vibrational properties, for example of magnetocaloric systems.

MS Mössbauer spectroscopy

This method is based on Mössbauer effect, i.e. the resonant and recoil-free emission and absorption of gamma rays in atomic nuclei in solid material (Nobel prize in physics 1961). By recording absorption or emission spectra, it's possible to examine a number of hyperfine interactions, allowing conclusions regarding e.g. the chemical surrounding, magnetic and valence state of the Fe-atoms. As Mössbauer spectroscopy is an isotope-specific method, it is possible to incorporate tracer layers of the Mössbauer isotope (⁵⁷Fe and ¹¹⁹Sn in our group) at certain positions within a thin film sample to study the magnetic properties at precisely defined locations and interfaces.

AFM, XRD, XPS, LEED, RHEED, MEED, AES Sample characterization

Further methods to characterize samples include atomic force microscopy (AFM), X-ray diffraction (XRD), electron diffraction (LEED, RHEED, MEED), X-ray photoelectron spectroscopy (XPS), and Auger electron spectroscopy (AES).

SQUID, VSM Magnetometry

In addition to element specific methods, classic magnetometry is utilized to characterize the macroscopic magnetic properties of samples at high magnetic fields (up to 9T) over a wide range of temperatures (1.8-1000K). For this purpose, we use a highly sensitive SQUID magnetometer for DC and AC measurements, as well as a shared VSM. The use of SQUID-based AC-susceptometry allows a detailed characterization of dynamic magnetic properties e.g. of ferrofluid systems, while measurements of the converse magnetoelectric effect are possible thanks to a self-built measurement option.