Calculating Stray Field And Analyzing Magnetic Domain Structure By MFM Image

There is larger correlation between the magnetic properties of the magnetic material and its fine magnetic domain structure, therefore, study the magnetic domain structure of materials have great significance in understanding magnetic properties of nanoscale magnetic material. The magnetic force microscopy (MFM) is an important instrument to observe the magnetic material surface micromagnetic structure. The MFM can not give the magnetic domain structure directly, but give the interaction between magnetic charges of the sample surface and magnetic probe. Therefore, the development and improvement of the methods of analysis of MFM images is beneficial to the study of the magnetic domains. Based on the simplified magnetic probe model, the surface of the stray field of the magnetic thin film sample can be calculated from the magnetic force microscopy image, and according to the distribution of the stray field the magnetic domain structure can be inferred and determined.First, the MFM image can be considered as the convolution of the MFM tip’s Green’s function and the magnetic charge of the sample surface, for the convenience of calculation, a simplified probe model of a magnetic monopole type tip is effective in the deconvolution method, then we can obtainthe magnetic charge distribution of the sample surface. The magnetic potential of the space above the sample surface satisfy the Laplace equation, which has a boundary condition with the distribution of magnetic charge. By using discrete Fourier transform (DFT) method, the magnetic potential distribution can be derived, and thestray field distribution of the sample surface is the gradient of magnetic potential distribution.After that, we select a MFM image of sample witha thickness of460nm FeCoZr thin film. Using the method above,the stray field of the sample can be calculated. By analyzing the characteristics of thestray fielddistribution, it’s believed that two different magnetic moment distributions can generate the stray field of such a feature. One kind of magnetic configuration is a typicalBloch magnetic domain structure, another is the sinusoidal distribution of magnetic moments resulting from the perpendicular magnetic anisotropy. Combining magnetic properties and other measured values of the sample, we can estimate the energy density value of the two kinds of the magnetic domain structure. It’sconcluded that the smaller energy value of two is the actual magnetic domain structure of the sample, and in this way we can determine the magnetic domain structure of the magnetic thin film sample an MFM image.At last, we calculated the stray field distribution of Co/Pd bit patterned media and compared with the stray field of ideal bit patterned media, and we found the two results agreed well.