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Nanomagnetism at NIST: Magnetic Domains
In general, magnetic materials form domains. How they do so is extremely important to understand how magnetic devices perform, particularly on the nanoscale. NIST uses and develops a variety of measurement techniques to understand domains in nanoscale systems and the domain walls that separate different domains. These walls can be as thin as a nanometer. Magnetic Force Microscopy (MFM) is a commonly used technique that is able to measure magnetic structures with nanometer resolution. MFM measures the interaction of magnetic fields of the sample with the magnetization of the tip. Scanning Electron Microscopy with Polarization Analysis (SEMPA ) is a high resolution magnetic microscopy technique that was developed at NIST. SEMPA measures the magnetization pattern through the polarization of the secondary electrons in an electron microscope. NIST has carried out a quantitative comparison between SEMPA and MFM to relate measurements of the fringing fields to the magnetization pattern. Two optical techniques that do not have nanometer resolution but which can be used to image ultrathin films are the MagnetoOptical Indicator Film (MOIF) technique and Magneto-Optic Microscopy.
Calculations of the the domain patterns play an important role in understanding the behavior of nanomagnetic structures. NIST has developed software to compute such patterns: the Object-Oriented MicroMagnetics Framework (OOMMF). This software is widely used in the community to augment measurements of magnetic properties on the nanoscale. To help the community establish the reliability of such techniques, NIST has developed a series of standard problems that have been used to compare different codes and validate them as accurately solving the mathematically defined problem.