scientific staff

Dr. Volker Neu

Dr. Ulrike Wolff

Silvia Vock

Fabian Rhein

technical staff

Katja Berger

LT-MFM


Many magnetic materials show interesting phenomena at low temperatures and high magnetic fields.

  • Temperature and field dependent observation of the domain structure of CoPt/Ru multilayers

CoPt/Ru multilayers exhibit a broad range of fascinating magnetic structures. In zero field, two distinctly different magnetic states, antiferromagnetic coupled and ferromagnetic coupled, are observed which depend on temperature and magnetic history, but possess vanishing remanence and are therefore best studied by direct imaging of the domain structure.

µ0H=0 Tµ0H=0.3 T220 K
  • Temperature dependent switching behaviour of ferromagnetic CoPt stripes

In small structured Co/Pt stripes the magnetoresistive behaviour is governed by a combination of anisotropic magnetoresistance and domain wall resistance. In order to support the interpretation of magnetoresistive measurements, the magnetization process in Co/Pt stripes with perpendicular magnetic anisotropy and varying stripe width (0.3 - 2.2 µm) was investigated. At various temperatures the Co/Pt stripes were magnetized in a field of 1 T and MFM measurements were subsequently performed during demagnetizing field sweeps. Whereas the coercivity does not depend strongly on the stripe width, the magnetization process is strongly different for narrow and wide Co/Pt stripes. At 10 K the 300 nm narrow stripes switch via the nucleation of a reversed domain over the whole width of the stripe, and subsequent domain wall movement along the length of the stripe (see right image). The wider stripes form a more complicated, 2-dimensional domain pattern during magnetization reversal (see left image).

10 K

  • Vortex imaging in YBCO high-Tc superconductor thin films using low-temperature scanning probe microscopy

The main goal of this research topic is to improve the understanding of the impact of nanostructuring on the performance of YBCO high temperature superconductors. A comprehensive understanding of the mechanism for vortex pinning at natural and artificial defects provides the possibility to improve the magnitude of the critical current density. We are performing magnetic force microscopy (MFM) imaging of vortex structure with a low-temperature scanning probe microscope (Cryogenic SFM, Omicron). This microscope allows scanning at different temperatures (7 K – 300 K) and in magnetic fields up to 7 T. On the 4x4 µm2 MFM image of the off-axis pulsed laser deposited (PLD) YBCO-film cooled down to the temperature of about 8 K in a magnetic field of 3 mT one can clearly see the vortex structure. See T. Shapoval, et.al., Physica C, in press