Magnetic patterns in hydrothermal ferrites by magnetic force microscopy
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J.M.C. Vilela and M.S. Andrade STM/CETEC, Av. José Cândido da Silveira 2000, Belo Horizonte-MG, 31170-000, Brazil (Received 1 August 2001; accepted 26 March 2002)
Magnetic structure and domains of hydrothermal NiZn ferrites were studied through magnetic force microscopy by using different magnetically characterized tips. The magnetic patterns varied according to the tip employed and were correlated to the magnetic induced field generated by these different coated tips. Low-moment tips were found to be the most adequate to study magnetic domains in these hydrothermal ferrites.
Magnetic force microscopy (MFM) is a scanning probe microscopy method that utilizes the long-range dipolar force interaction between a sample and a magnetic probe to image the magnetic configuration or the domains structure of the sample. The measurement principle is based on the fact that the interaction force (magnetic) between tip and sample causes a shift of the resonance frequency of the cantilever, which can be detected and used for image formation. MFM has become a widespread and easy to use tool for the characterization of low-dimensional magnetic structures down to the nanometer scale, correlating topographic, and magnetic structures of materials without requiring special sample preparation. Nowadays, the literature about MFM is very impressive,1,2 with studies in various recording media, materials, superconductors, and small particles. Other applications include characterization of media noise, write/ read media and head testing,3 as well as local magnetic flux source for testing the sensitivity of a read sensor or to observe the field from the write head operating at frequencies as high as 1 GHz.4 Today, the main obstacle to even more widespread MFM use seems to be interpretational issues. Quantitative interpretation of MFM images remains difficult, since it involves nonlinear interactions, i.e., the magnetic state of both tip and sample changes during the imaging process.5,6 However, these mutual interactions or “perturbations” can be advantageously used to study the micromagnetic properties of a given material. The perturbations lead to magnetic dissipation, domain contrast, and magnetic reversals, which are current topics of research.7 One way to understand the magnetic structure of a sample is to use a tip with a coercivity that is very different from that of the sample, either much lower or much higher. Then, when the a)
Address all correspondence to this author. e-mail: [email protected]. J. Mater. Res., Vol. 17, No. 6, Jun 2002
contrast is changing as a function of tip, one can be relatively confident of the origin of the change (applied field imaging).7,8 In this work, the magnetic structure of hydrothermal NiZn ferrites was studied by using magnetically characterized tips. The resulting images were interpreted by considering the tip/sample interactions and its relevance to the discussion of the experimental results. NiZn ferrites were hydrothermally produced at 200 °C, according to procedures previously described,9
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