Frequency-Induced Bulk Magnetic Domain-Wall Freezing Visualized by Neutron Dark-Field Imaging

B. Betz, P. Rauscher, R. P. Harti, R. Schäfer, H. Van Swygenhoven, A. Kaestner, J. Hovind, E. Lehmann, and C. Grünzweig

Phys. Rev. Applied 6, 024024 – Published 30 August 2016

Abstract

We use neutron dark-field imaging to visualize and interpret the response of bulk magnetic domain walls to static and dynamic magnetic excitations in (110)-Goss textured iron silicon high-permeability steel alloy. We investigate the domain-wall motion under the influence of an external alternating sinusoidal magnetic field. In particular, we perform scans combining varying levels of ${dc}_{offset}$ $(0 - 30 A / m)$ , oscillation amplitude $A_{ac}$ $(0 - 1500 A / m)$ , and frequency $f_{ac}$ ( $(0 - 200 Hz)$ . By increasing amplitude $A_{ac}$ while maintaining constant values of ${dc}_{offset}$ and $f_{ac}$ , we record the transition from a frozen domain-wall structure to a mobile one. Vice versa, increasing $f_{ac}$ while keeping $A_{ac}$ and ${dc}_{offset}$ constant led to the reverse transition from a mobile domain-wall structure into a frozen one. We show that varying both $A_{ac}$ and $f_{ac}$ shifts the position of the transition region. Furthermore, we demonstrate that higher frequencies require higher oscillation amplitudes to overcome the freezing phenomena. The fundamental determination and understanding of the frequency-induced freezing process in high-permeability steel alloys is of high interest to the further development of descriptive models for bulk macromagnetic phenomena. Likewise, the efficiency of transformers can be improved based on our results, since these alloys are used as transformer core material.

Received 29 December 2015

DOI:https://doi.org/10.1103/PhysRevApplied.6.024024

Physics Subject Headings (PhySH)

Magnetic domains

Interferometry Neutron imaging

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

B. Betz^1,2, P. Rauscher³, R. P. Harti¹, R. Schäfer⁴, H. Van Swygenhoven^2,5, A. Kaestner¹, J. Hovind¹, E. Lehmann¹, and C. Grünzweig¹

¹Paul Scherrer Institut, LNS, Neutron imaging and Activation Group, CH-5232 Villigen, Switzerland
²Ecole polytechnique fédérale de Lausanne, NXMM, IMX, CH-1015 Lausanne, Switzerland
³Fraunhofer IWS Dresden, Laser Ablation and Cutting, D-01069 Dresden, Germany
⁴Leibniz Institute for Solid State and Materials Research (IFW) Dresden, D-01069 Dresden, Germany, and Institute for Materials Science, TU Dresden, D-01069 Dresden, Germany
⁵Paul Scherrer Institut, Photons for Engineering and Manufacturing, CH-5232 Villigen, Switzerland

Magnetization Response of the Bulk and Supplementary Magnetic Domain Structure in High-Permeability Steel Laminations Visualized In Situ by Neutron Dark-Field Imaging

B. Betz, P. Rauscher, R. P. Harti, R. Schäfer, A. Irastorza-Landa, H. Van Swygenhoven, A. Kaestner, J. Hovind, E. Pomjakushina, E. Lehmann, and C. Grünzweig

Phys. Rev. Applied 6, 024023 (2016)

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Vol. 6, Iss. 2 — August 2016

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Images

Figure 1
Schematic of the neutron-grating interferometer for the investigation of the bulk magnetic domain structure under the influence of externally applied alternating magnetic fields with varying parameters ${dc}_{offset}$ , $A_{ac}$ , and $f_{ac}$ as explained in the inset. The source grating $G_{0}$ is placed at a distance $l$ from the phase grating $G_{1}$ , which is followed by the analyzer grating $G_{2}$ at the Talbot distance $d_{T}$ . The sample is mounted in the magnetization frame and placed as close as possible in front of $G_{1}$ . The images are recorded using a scintillator-based neutron imaging detection system.
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Figure 2
Data-acquisition matrix for the ${dc}_{offset}$ ,the oscillation amplitude $A_{ac}$ , and frequency $f_{ac}$ of the alternating sinusoidal magnetic field. Each sphere represents DFI measurement. The red spheres mark the ${dc}_{offset}$ scan, blue spheres represent the isofrequency scan at a fixed frequency of $f_{ac} = 20 Hz$ with increasing oscillation amplitude, green spheres illustrate the isoamplitude scan at a fixed amplitude $A_{ac} = 225 A / m$ with increasing frequency, and orange spheres indicate the completing isofrequency scans.
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Figure 3
Static visualization of the bulk domain-wall structure and response to an applied ${dc}_{offset}$ . DFIs for increasing field values from ${dc}_{offset} = 0$ to $30 A / m$ are shown (red spheres in Fig. 2). Large vertically elongated domains are depicted by black lines, representing the domain walls. Misoriented grains appear as dark areas.
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Figure 4
DFIs of the isofrequency scan (blue spheres in Fig. 2) at $f_{ac} = 20 Hz$ and ${dc}_{offset} = 4.5 A / m$ . Stationary domain walls are observed until the amplitude in the transition region ( $A_{ac} = 450 A / m$ ) starts to excite the domain walls, causing them to tremble. A further increase in amplitude leads to a mobilization of the basic domain walls, seen as a gray veil that represents the average position of the domain walls during the scan.
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Figure 5
Frequency-induced bulk magnetic domain-wall freezing. DFIs of an isoamplitude-scan (green spheres in Fig. 2) at a ${dc}_{offset} = 4.5 A / m$ and an $A_{ac} = 225 A / m$ . At low frequencies, domain walls are mobilized. The transition into a frozen domain structure is observed between 5–10 Hz. For higher frequencies, the domain walls stay frozen and no significant changes in the DFIs are recorded.
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Figure 6
Data-acquisition matrix showing the amplitude- and frequency-dependent shift in the transition between frozen and mobilized basic domain-wall structures. In the upper-left part of the figure with high frequencies and small amplitudes, frozen domain walls are observed. In the bottom-right part of the figure with large amplitudes and small frequencies, mobilized domain walls are seen. Representative isofrequency and isoamplitude scans are marked by the blue and green boxes, respectively. The DFIs showing the transition points are marked by purple dashed boxes.
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