Abstract
Magnetic force microscopy (MFM) is a widespread technique for imaging magnetic structures with a resolution of some 10 nanometers. MFM can be calibrated to obtain quantitative (qMFM) spatially resolved magnetization data in units of A/m by determining the calibrated point spread function of the instrument, its instrument calibration function (ICF), from a measurement of a well-known reference sample. Beyond quantifying the MFM data, a deconvolution of the MFM image data with the ICF also corrects the smearing caused by the finite width of the MFM tip stray field distribution. However, the quality of the calibration depends critically on the calculability of the magnetization distribution of the reference sample. Here, we discuss a Ti/Pt/Co multilayer stack that shows a stripe domain pattern as a suitable reference material. A precise control of the fabrication process, combined with a characterization of the sample micromagnetic parameters, allows reliable calculation of the sample’s magnetic stray field, proven by a very good agreement between micromagnetic simulations and qMFM measurements. A calibrated qMFM measurement using the Ti/Pt/Co stack as a reference sample is shown and validated, and the application area for quantitative MFM measurements calibrated with the Ti/Pt/Co stack is discussed.
Highlights
Magnetic force microscopy (MFM) is a versatile tool for imaging magnetic nanostructures [1] that is available in many laboratories
Point-probe models show a strong dependence on the feature size. This can be overcome by fully considering the non-local structure of the tip, which can be done through use of a transfer function (TF) approach [15,16]
We present a perpendicularly magnetized Ti/Pt/Co multilayer stack thin film material as a suitable reference sample candidate for TF based calibrations and will demonstrate that it fulfills the requirements discussed above
Summary
MFM is a versatile tool for imaging magnetic nanostructures [1] that is available in many laboratories. A calculability is, in particular, given for the special case of thickness-independent strictly perpendicular magnetization structures with either up or down magnetized domains and well-defined domain transitions Such a sample allows the re f calculation of the effective magnetic surface charge, σe f f , from the measured MFM phase re f shift image using the material parameters saturation magnetization, Ms , total magnetic re f layer thickness, dre f , and domain wall width, δDW. To this end, up- and down-magnetized areas of the sample are identified by a discrimination based on a threshold criterion, resulting in a binary matrix (1, −1). The application area in terms of accessible magnetic structure sizes covered by a calibration using the Ti/Pt/Co stack is discussed
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