Temperature influence on magnetic properties and magnetoimpedance effect of Fe-rich glass-coated microwires

Giant magnetoimpedance, GMI, effect and magnetic properties upon temperature influence of as-prepared and stress-annealed amorphous Fe75B9Si12C4 glass-coated microwires produced by the Taylor-Ulitovsky technique are analyzed. Remarkable change in the hysteresis loops and GMI effect is observed for both samples upon heating. Tuning of the stress-annealing conditions allows one to vary the temperature dependence. Furthermore, it is observed almost complete reversibility of the changes induced by the temperature. Observed dependences are explained by the heating effect on the internal stresses relaxation, by the modification of the thermal expansion coefficients of the metallic nucleus and the glass coating, and by the Hopkinson effectThis work was supported by EU under “INFINITE” (Grant No. HORIZON-CL5-2021-D5-01-06) project, by the Spanish MCIU under PGC2018-099530-B-C31 (MCIU/AEI/FEDER, UE), by the Government of the Basque Country under Grant No. PUE_2021_1_0009, Elkartek (MINERVA and ZE-KONP) projects and under the scheme of “Ayuda a Grupos Consolidados”(ref. IT1670-22), by the Diputación Foral de Gipuzkoa in the frame of Programa “Red guipuzcoana de Ciencia, Tecnología e Inno- vación 2021” under Grant No. 2021-CIEN-000007-01 project and by the University of Basque Country under Grant No. COLAB20/15 project. The authors thank for technical and human support pro- vided by SGIker of UPV/EHU (Medidas Magneticas Gipuzkoa) and European funding (ERDF and ESF). We would like to be grateful to the administration of the University of the Basque Country, which not only provides very limited funding, but even expropriates the resources received by the research group from private companies for the research activities of the group. Such interference helps keep us on our toes. The group at the Institute of Experimental Physics SAS acknowledges support of the projects VEGA 2/0171/19 and APVV-19-036

Effect of temperature on magnetic properties and magnetoimpedance effect of Co-rich glass-coated microwires

We studied the effect of heating on the magnetic properties and giant magnetoimpedance (GMI), effect of Co69.2Fe3.6Ni1B12.5Si11Mo1.5C1.2 glass-coated microwires with vanishing magnetostriction. We observed, that upon heating the hysteresis loop changed its shape from inclined to rectangular. These changes in hysteresis loop shape correlate with modification of magnetic field dependencies of GMI ratio, ΔZ/Z, from double-peak to single-peak and with change in value of maximum GMI ratio. The origin of the observed changes in the hysteresis loop and the GMI effect is discussed in terms of the Hopkinson effect, internal stresses relaxation upon heating, and the temperature dependencies of internal stresses and the magnetostriction coefficient

Study of the induced anisotropy in field annealed hitperm alloys by mössbauer spectroscopy and kerr microscopy

Samples of FeCoNbBCu alloy were nanocrystallized under zero field annealing (ZF) and transverse field annealing (TF) conditions. A reduction in coercivity for TF samples with respect to ZF sample (16 and 45 A/m, respectively) is observed. Kerr microscopy images show a well-defined parallel domain structure, transversally oriented to the ribbon axis for the TF sample unlike for the ZF sample, for which a complex pattern is observed with large and small domains at the surface of the ribbon. Although Mössbauer spectra are clearly different for the two studied samples, Mössbauer studies confirm that there is no significant difference between the hyperfine field distributions of TF and ZF samples but only the relative intensity of the 2nd and 3rd lines A (related to the angle between the gamma radiation and the magnetic moments, α). However, for TF annealed samples α = 90 deg (A = 4), indicating that the magnetic moments lay on the plane of the ribbon in agreement with the well-defined domain structure observed by Kerr microscopy, ZF annealed samples show A = 1.8. This value is close to that of a random orientation (A = 2) but smaller, indicating a slight preference for out of plane orientations. Moreover, it is clearly smaller than that of the as-cast amorphous samples A = 2.8, with a preference to in-plane orientations. The application of the law of approach to saturation yields a larger effect of the inhomogeneities in ZF sample with respect to TF one.This work was supported by the Spanish Ministry of Science and Innovation and EU FEDER (Project MAT2013-45165-P), the PAI of the Regional Government of Andalucía, and the Slovak Projects APVV-0492-11, VEGA 2/0192/13. The Slovak team acknowledges also the support of the Operational Program “Research and Development” financed through European Regional Development Fund through the Projects ITMS 26220120019 and ITMS 26220220061

Anisotropy field distribution in soft magnetic Hitperm alloys submitted to different field annealing processes

The magnetic anisotropy field distribution is discussed for Hitperm alloys annealed under different field conditions leading to different induced magnetic anisotropies: zero (ZF), transversal (TF), and longitudinal (LF) field annealing and compared to that of as-quenched (AQ) melt-spun amorphous ribbon. In order to accurately use the present method, the demagnetizing factor has been obtained by analyzing the field dependence of the inverse of the field derivative of the magnetization. The coherence of the analysis is supported by testing the normalization of the complete distribution of anisotropy fields. Independently of the composition, two groups can be distinguished among the studied samples: those with mainly perpendicular anisotropy field contributions (ZF and TF samples) and those with mainly longitudinal anisotropy field contributions (LF and AQ samples). Behavior of TF samples is well reproduced using Stoner-Wohlfarth model and, in the case of as-quenched amorphous samples, the anisotropy field depends almost linearly on the thickness of the ribbon.Work supported by the Spanish MINECO and EU FEDER (Project MAT 2013-45165-P), the PAI of the Regional Government of Andalucía and the Slovak projects APVV-0492-11, VEGA 2/0192/13. The Slovak team acknowledges also the support of the Operational Program “Research and Development” financed through European Regional Development Fund through the projects ITMS 26220120019 and ITMS 26220220061