Program Highlights

Spin-Polarized Scanning Tunneling Microscopy

Axel Enders and Ralph Skomski
Nebraska MRSEC

 Dirk Sander and Jürgen Kirschner
Max Planck Institute for Microstructure Physics, Halle, Germany

The visualization of magnetism and magnetic phenomena with ultimate precision is of utmost importance to improve our atomic-scale understanding of the origin of magnetic phenomena, such as the exchange interaction and magnetic anisotropy. Nebraska MRSEC researchers are using a scanning tunneling microscope (STM) to simultaneously map the structure and the magnetism of surfaces and nanostructures with sub-nanometer resolution. One example is the surface of a single crystal of antiferromagnetic chromium exhibiting atomically smooth terraces at its surface, where the magnetization of adjacent terraces is always in opposite direction. The magnetic contrast was achieved using STM tips consisting of antiferro­magnetic chromium. Using magnetic tips, the tunnel current becomes dependent on the relative orientation of the magnetization of the tip apex and the sample, as a result of the magnetic tunnel resistance effect.

Upon improving further the quality of the tips, magnetic imaging with ultimate atomic resolution will soon be possible. This will enable atomic-level magnetic investigations of nanostructures that exhibit unexpected and unusual magnetic properties, such as the recently discovered antiferromagnetic cobalt dots and nanomagnetic skyrmions (J. Phys.: Condens. Matter 22, 433001 (2010)].

These programs are supported by the National Science Foundation, Division of Materials Research, Materials Research Science and Engineering Program, Grant 0820521.

Topography of a Cr(0001) surface (left) and a spin-resolved spectroscopy map of a similar surface area of the same sample (right). The magnetic contrast is based on the tunnel magnetoresistance of the junction formed of the magnetic STM tip, the vacuum gap and the sample. Bright/dark contrast appears if the magnetization of tip and the sample are aligned parallel/antiparallel.