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Description
Annealing of amorphous Vitroperm-800 alloy in the form of thin ribbons under tensile stress is very effective way of achieving huge value of magnetic anisotropy, which may well exceed the value of magneto-crystalline constant (8 kJ/m$^3$) of Fe-Si crystalline phase [1]. As a result of such thermo-mechanical treatment ribbons reveal perfectly linear hysteresis loop with constant slope (permeability) which can be controlled by applied stress. It has been shown in our recent work [2] that such stress induced anisotropy (SIA) is because Fe$_{3}$Si nanocrystalline grains growing in the tensile direction have a higher value of the lattice spacing as in case of transversal direction, where opposite behavior is seen. Furthermore it was demonstrated that the strain partitioning among different Bragg reflections of Fe$_{3}$Si phase is not even, and the magnitude of the SIA for a given set of Bragg reflections $\{hkl\}$ is inversely proportional to its Young’s modulus $E_{hkl}$.
In this work the emphasis was placed at the study of relaxation process of SIA during thermal cycling. Nanocrsytalline ribbons with different levels of SIA were prepared by annealing amorphous Fe$_{73.6}$Cu$_{1}$Nb$_{3}$Si$_{15.5}$B$_{6.9}$ alloy at two different stresses, i.e. 14 MPa and 482 MPa. Temperature-time behavior of the SIA was recorded during in-situ XRD experiments when exposing specimen to thermal cycling (20 -> 550 -> 100 -> 550 $^\circ$C). In-situ XRD experiments were done at the P02.1 beamline of the PETRA III synchrotron storage ring at DESY in Hamburg, Germany. It was found that the relaxation process starts with an increase in the values of SIA across all Bragg reflections of Fe$_{3}$Si cubic phase. After reaching temperature of 400 $^\circ$C magnitude of the SIA tends to decrease with temperature increasing up to 500 $^\circ$C (see Fig.1). Following cooling down to 100 $^\circ$C and heating back to 500 $^\circ$C yield, within an experimental error, similar behaviors. Similar trends, however with different magnitudes of SIA, are observed for all Bragg reflections of Fe$_{3}$Si cubic phase.
Fig. 1 Temperature dependence of the relative magnitude |SIA| as determined for the (620) Bragg reflection of Fe$_{3}$Si cubic phase.
Acknowledgements
Vitroperm-800 alloy in the form of thin ribbon was kindly provided by Dr. G. Herzer from VACUUMSCHMELZE GmbH Hanau, Germany. This research was financially supported by a Slovak Scientific Grant Agency VEGA (project No. VEGA 1/0638/24).
References
[1] G. Herzer, V. Budinsky, and C. Polak, “Magnetic properties of nanocrystalline FeCuNbSiB with huge creep induced anisotropy,” Journal of Physics: Conference Series, vol. 266. IOP Publishing, p. 012010, Jan. 01, 2011. doi: 10.1088/1742-6596/266/1/012010.
[2] D. Yudina, M. Marsilius, and J. Bednarcik, “Structural aspects of stress-induced magnetic anisotropy in Fe-based nanocrystalline alloy,” Journal of Alloys and Compounds, vol. 960. Elsevier BV, p. 171011, Oct. 2023. doi: 10.1016/j.jallcom.2023.171011.
