Observation of Patterns by Magnetic Force Microcopy in Fe-alloys with Shape Memory Effect
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Observation of Patterns by Magnetic Force Microcopy in Fe-alloys with Shape Memory Effect M. I.N. da Silva, J. C. González and M. S. Andrade1 North Carolina State University, Analytical Instrumentation Facility, Raleigh, NC, 27695-7531, U.S.A. 1 Laboratório de Nanoscopia, Setor de Tecnologia Metalúrgica – CETEC, Av. José Cândido da Silveira, 2000, Belo Horizonte-MG, 31170-000, Brazil.
ABSTRACT
In this study, we investigated the magnetic domains of a FeMnSiNiCr stainless steel sample using Magnetic Force Microscope (MFM). We compared the magnetic patterns obtained by scanning the sample with three coated probes with different magnetic properties: Medium magnetic moment (MM), low magnetic moment (LM), and low coercivity (LC). The probesurface separation was varied between 25 to 300 nm in order to quantify the magnetic microstructure of the sample. A simple model for the probe-sample interaction was used to interpret the contrast change as a function of the probe-surface separation. The experiment showed that the average maximum frequency decreases with the probe-surface separation and the intensity of the frequency is the strongest for the MM probe. X ray diffraction experiments were used to identify the different phases present in the sample. The X-ray diffraction experiments together with the MFM showed that α-phase islands surrounded by a γ-phase matrix are responsible for the magnetic properties of the sample.
INTRODUCTION Magnetic force microscopy (MFM) has proven to be a useful tool for imaging the magnetic microstructures in a variety of magnetic materials [1]. This technique has characteristics such as high spatial resolution and minimum sample preparation. MFM is based on the interaction between a magnetic sample and a magnetic coated Atomic Force Microscopy (AFM) probe or tip. The AFM tip can be coated with a variety of materials with different magnetic properties. The contrast observed in this kind of microscopy depends strongly of the magnetic interaction between the sample and the AFM tip as well as the modifications that the magnetic AFM tip can induce on the magnetic microstructure of the sample. The choice of magnetic coating for the AFM tip can reveal fine microstructure in the magnetic domains of the sample or simply modify the microstructure itself. In this work, the magnetic domains of a FeMnSiNiCr stainless steel sample were studied using the MFM technique. This Fe-based alloy has great technological importance due to the Shape Memory Effect (SME) present in this steel [2]. We compared the magnetic patterns obtained by scanning the sample with three coated probes with different magnetic properties: Medium magnetic moment (MM), low magnetic moment (LM), and low coercivity (LC). The tip-surface separation was varied from 25 to 300 nm in order to quantify the magnetic microstructure of the sample. A simple model for the magnetic tip-sample U7.4.1
interaction was used to interpret the contrast change as a function of the tip-surface separation, for all the three AFM tips. X ray diffraction experi
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