Epstein frame investigation on soft magnetic properties of Fe-based amorphous strips

Fe-based amorphous strip (AM strip) is a core material for high-efficiency distribution transformers and contributes to saving energy loss in electricity distribution. The core loss and apparent power for 2605SA1 amorphous strips at power frequency are studied using the Epstein frame method. Longitudinal magnetic field annealing and the influence of measuring modes on test results are investigated in detail. Improved test efficiency and higher accuracy in test results for amorphous ribbons are demonstrated and it is found that the number of strips and the lap joint methods affect the test results greatly. The waveform of the secondary induction voltage becomes sinusoidal with the increase of strip number. The values of core loss and apparent power become stable once the total number of strips is larger than 20. The coefficient of eddy current loss (e) also affects the correction of testing core losses. The test results could be improved at a smaller value of e when the waveform of the secondary induction voltage becomes deformed from sinusoidal due to a lower number of strips (below 20). The measured results were found to be reproducible when the strip number of each layer was one or two. However, the core loss and the apparent power increased along with the increase in the number of strips in each layer. Moreover, demagnetisation showed no effects on the test results when using the Epstein frame method.

Effects of Perpendicular Magnetic Field Annealing on the Structural and Magnetic Properties of [Co/Ni]2/PtMn Thin Films

In this study, [Co/Ni]2/PtMn thin films with different PtMn thicknesses (2.7 to 32.4 nm) were prepared on Si/SiO2 substrates. The post-deposition perpendicular magnetic field annealing (MFA) processes were carried out to modify the structures and magnetic properties. The MFA process also induced strong interlayer diffusion, rendering a less sharp interface between Co and Ni and PtMn layers. The transmission electron microscopy (TEM) lattice image analysis has shown that the films consisted of face-centered tetragonal (fct) PtMn (ordered by MFA), body-centered cubic (bcc) NiMn (due to intermixing), in addition to face-centered cubic (fcc) Co, Ni, and PtMn phases. The peak shift (2-theta from 39.9° to 40.3°) in X-ray diffraction spectra also confirmed the structural transition from fcc PtMn to fct PtMn after MFA, in agreement with those obtained by lattice images in TEM. The interdiffusion induced by MFA was also evidenced by the depth profile of X-ray photoelectron spectroscopy (XPS). Further, the magnetic properties measured by vibrating sample magnetometry (VSM) have shown an increased coercivity in MFA-treated samples. This is attributed to the presence of ordered fct PtMn, and NiMn phases exchange coupled to the ferromagnetic [Co/Ni]2 layers. The vertical shift (Mshift = −0.03 memu) of the hysteresis loops is ascribed to the pinned spins resulting from perpendicular MFA processes.