Review of Helical Magnetic Structures in Magnetic Microwires

We provide an overview of the helical magnetic structures in magnetic microwires. Having analyzed the experimental data describing the magnetic behavior of magnetic microwires since the 1990s, we found indirect evidence of the existence of various types of helical magnetic structures. Purposeful research has allowed us to discover the spiral magnetic structure as one of the most unusual helical structures. A comparison of the spiral structure with another type of helical structure—elliptical—was carried out. In the analysis, emphasis was placed on the length of the domain wall as one of the most important parameters. The difference in the dynamic properties of the spiral and elliptical domain walls has been demonstrated.This research was funded by the Spanish MCIU, under PGC2018-099530-B-C31 (MCIU/AEI/FEDER, UE), by the EU under the “INFINITE”(Horizon 2020) project, by the Government of the Basque Country, under the PUE_2021_1_0009 and Elkartek (MINERVA, ZE-KONP and COMPONENS) projects, by the University of the Basque Country, under the scheme of “Ayuda a Grupos Consolidados” (Ref.: GIU18/192) and under the COLAB20/15 project and by the Diputación Foral de Gipuzkoa in the frame of Programa “Red guipuzcoana de Ciencia, Tecnología e Innovación 2021” under the 2021-CIEN-000007-01 project

Manipulation of domain wall dynamics in amorphous microwires through the magnetoelastic anisotropy

We studied the effect of magnetoelastic anisotropy on domain wall (DW) dynamics and remagnetization process of magnetically bistable Fe-Co-rich microwires with metallic nucleus diameters (from 1.4 to 22 mu m). We manipulated the magnetoelastic anisotropy applying the tensile stresses and changing the magnetostriction constant and strength of the internal stresses. Microwires of the same composition of metallic nucleus but with different geometries exhibit different magnetic field dependence of DW velocity with different slopes. Application of stresses resulted in decrease of the DW velocity, v, and DW mobility, S. Quite fast DW propagation (v until 2,500 m/s at H about 30 A/m) has been observed in low magnetostrictive magnetically bistable Co56Fe8Ni10Si10B16 microwires. Consequently, we observed certain correlation between the magnetoelastic energy and DW dynamics in microwires: decreasing the magnetoelastic energy, K (me), DW velocity increases.This work was supported by the EU ERA-NET programme under project 'SoMaMicSens' (MANUNET-2010-Basque-3), by the Spanish MICINN under project MAT2010-18914, and by the Basque Government under Saiotek 10 MIMAGURA project

Magnetic microwires with unique combination of magnetic properties suitable for various magnetic sensor applications

There is a pressing demand to improve the performance of cost-effective soft magnetic materials for use in high performance sensors and devices. Giant Magneto-impedance effect (GMI), or fast single domain wall (DW) propagation can be observed in properly processed magnetic microwires. In this paper we have identified the routes to obtain microwires with unique combination of magnetic properties allowing observation of fast and single DW propagation and GMI effect in the same microwire. By modifying the annealing conditions, we have found the appropriate regimes allowing achievement of the highest GMI ratio and the fastest DW dynamics. The observed experimental results are discussed considering the radial distribution of magnetic anisotropy and the correlation of GMI effect, and DW dynamics with bulk and surface magnetization processes. Studies of both Fe- and Co-rich microwires, using the magneto-optical Kerr effect, MOKE, provide information on the magnetic structure in the outer shell of microwires. We have demonstrated the existence of the spiral helical structure in both studied microwires. At the same time, torsion mechanical stresses induce helical bistability in the same microwires, which allow us to consider these microwires as materials suitable for sensors based on the large Barkhausen jump.This work was funded by Spanish MCIU under PGC2018-099530-B-C31 (MCIU/AEI/FEDER, UE) by the Government of the Basque Country under PIBA 2018-44 project and Elkartek (CEMAP and AVANSITE) projects and by the University of Basque Country under the scheme of “Ayuda a Grupos Consolidados” (Ref.: GIU18/192)

Determination of Magnetic Structures in Magnetic Microwires with Longitudinally Distributed Magnetic Anisotropy

We studied the magnetic properties of a glass-covered amorphous microwire that was stress-annealed at temperatures distributed along the microwire length. The Sixtus-Tonks, Kerr effect microscopy and magnetic impedance techniques have been applied. There was a transformation of the magnetic structure across the zones subjected to annealing at different temperatures. The annealing temperature distribution induces the graded magnetic anisotropy in the studied sample. The variety of the surface domain structures depending on the longitudinal location has been discovered. Spiral, circular, curved, elliptic and longitudinal domain structures coexist and replace each other in the process of magnetization reversal. The analysis of the obtained results was carried out based on the calculations of the magnetic structure, assuming the distribution of internal stresses.This work was supported by EU under “INFINITE” (HORIZON-CL5-2021-D5-01-06) project, by the Spanish MICIN, under PID2022-141373NB-I00 project and by the Government of the Basque Country under PUE_2021_1_0009 and Elkartek (MINERVA, ZE-KONP AND COMPONENS) projects under the scheme of “Ayuda a Grupos Consolidados”(ref. IT1670-22)

Reversible and Non-Reversible Transformation of Magnetic Structure in Amorphous Microwires

We provide an overview of the tools directed to reversible and irreversible transformations of the magnetic structure of glass-covered microwires. The irreversible tools are the selection of the chemical composition, geometric ratio, and the stress-annealing. For reversible tuning we use the combination of magnetic fields and mechanical stresses. The studies were focused on the giant magnetoimpedance effect and the velocity of the domain walls propagation important for the technological applications. The essential increase of the giant magnetoimpedance effect and the control of the domain wall velocity were achieved as a result of the use of two types of control tools. The performed simulations reflect the real transformation of the helical domain structures experimentally found.This research was funded by National Science Centre Poland under Grant No. DEC-2016/22/M/ST3/00471, Spanish MCIU under PGC2018-099530-BC31 (MCIU/AEI/FEDER, UE), the Government of the Basque Country under PIBA 2018-44 projects. The authors thank for technical and human support provided by SGIker of UPV/EHU and European funding (ERDF and ESF). The research of P.G. was supported in part by PL-Grid Infrastructure

Magnetic Characterization in the Rayleigh Region of Nanocrystalline Magnetic Cores

We report on the structural and magnetic characterization of two nanocrystalline Finemet-type magnetic cores. The nanocrystalline structure developed after annealing the amorphous precursor alloy at 550 degrees C for 30 and 60 min of annealing time. Structural analysis carried out by means of X-ray diffraction providing useful information on the grain size mean and partial volume of the nanocrystalline phase. The magnetic characterization was focused mainly in the Rayleigh region which, influenced by the intergranular coupling, was found to be more efficient in the sample treated for a longer time with a finer nanocrystalline structure.This work was supported by the University of the Basque Country Government under the scheme "ayuda a grupos consolidados (Ref.: PPG17/35 and PIBA 2018-44 projects. Technical and human support provided by SGIker (UPV/EHU,) is gratefully acknowledged. The authors are grateful for technical and human support provided by SGIker of UPV/EHU (Medidas Magneticas Gipuzkoa) and European funding (ERDF and ESF).