Introduction to MFM	Instrumentation	Projects
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Projects

Domain Structure of Manganite Perovskites

Doped lanthan manganite perovskites exhibit a rich and complex phase diagram, which reflects the strong electron correlation in this material class. We investigate the domain structure after thermal demagnetization and in remanence as well as domain nucleation after saturation and domain growth while ramping an external magnetic field.

This study is done in cooperation with the Seoul National University, Korea.

See images in the gallery section.

MFM on High Tc-Superconductors

Most of the superconducting properties of cuprate superconductors like BSCCO and YBCO, which are extreme type-II superconductors depend on the behaviour of vortices. The magnetic field associated with such vortices can be detected by MFM. We study vortex pinning at columnar defects, vortex dynamics in external magnetic fields (Bean model) and the different vortex phases (Abrikosov lattice, vortex glass, vortex liquid).

This study is done in cooperation with the Seoul National University, Korea.

See images in the gallery section.

Exchange Force Microscopy

MFM is sensitive to long-range magnetostatic dipole interactions. Its resolution is limited to about 20 nm. Furthermore, antiferromagnets without stray field cannot be investigated. On the other hand, force microscopy in the dynamic mode in vacuum is capable of true atomic resolution in the non-contact regime on all types of surfaces.

Combining magnetic sensitivity with atomic resolution allows the detection of the very short-range exchange forces. Being directly sensitive to the spin-spin interaction means nothing less than ultimate achievable magnetic resolution.

Reorientation transition of ultrathin cobalt films on Au(111)

Ultrathin films with coverages in the monolayer regime can exhibit a thickness dependent reorientation transition between out-of plane and in plane magnetization. Such transitions have been observed on cobalt films with SEMPA. Shape anisotropy, substrate induced stress, growth mode, crystalline and interface anisotropies play an important role for the complex behavior of ultrathin films. With MFM film morphology and magnetic structure can be observed simultaneously and correlated with each other.

A commercial instrument operated in ultrahigh vacuum with in situ tip and sample preparation and a modified data acquisition software has been used in this investigation.

See images in the gallery section.

Domain writing with MFM on ultrathin cobalt films

Thin polycrystalline cobalt films has been prepared on silicon substrates. Magnetic domains could be induced in the film by touching the surface with the tip. We wrote different structures by means of magnetic lithography and studied several parameters -like time and applied force- which influence the appearance of the written structures.

A commercial instrument operated in ultrahigh vacuum with in situ tip and sample preparation and a modified data acquisition software has been used for this project.

See images in the gallery section.

Domain walls and ripple structure of thin cobalt films

Thin cobalt films have been investigated by means of eltron microscopy. In this study the high sensitivity and spatial resolution of MFM is used to investigate the fine structure of doamains and domain walls in this type of material. These films exhibit an in-plane magnetization with a ripple structure due to the superposition of shape anisotropy of the film and uniaxial anisotropy of the cobalt crystallites. Domains in such films are separated by complex cross tie domain walls.

All Investigations have been performed in the static mode under ambient conditions using a commercial instrument. The work has been done in cooperation with Siemens.

See images in the gallery section.

Switching behavior of single domain particles

Electron beam lithography allows to produce well defined ferromagnetic nanostructures. In particularly, large regular arrays of single domain particles can be made. We investigated the size dependent transition from multi domain to the single domain state, as well as the magnetic dipole interaction between those particles and their switching behavior in external magnetic fields.

A commercial instrument operated in ambient conditions has been equipped with a home built solenoid to apply small external magnetic fields. The work has been done in cooperation with Prof. Weiss.

See images in the gallery section.

Investigation of magnetic bit structures

MFM is an ideal tool to investigate magnetic bit structures. Like the read head of magnetic storage devices (hard disc or tape) it senses the magnetic stray field above the surface. However, its resolution is much better. Therefore it is used in this project to study to the interaction between closely spaced magnetic bits. The ultimate goal is to develop materials which allow to increase the bit density.

All Investigations have been done in cooperation with leading manufacturers of magnetic storage devices. The experiments have been performed under ambient conditions using a commercial instrument.

See images in the gallery section.

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