Structural, magnetic characterization (dependencies of coercivity and loss with the frequency) of magnetic cores based in Finemet

• Published in: Journal of magnetism and magnetic materials Vol. 443; pp. 124 - 130
• Main Authors: Osinalde, M., Infante, P., Domínguez, L., Blanco, J.M., del Val, J.J., Chizhik, A., González, J.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01-12-2017; Elsevier BV
• Subjects: Amorphous and nanocrystalline magnetic cores; Anisotropy; Annealing; Coercivity; Equivalence; Ferrous alloys; Grain size; Heat treatment; Induced magnetic anisotropy; Magnetic cores; Magnetic fields; Magnetic properties; Magnetism; Magneto-optic Kerr effect; Metallic glasses; Quenching; Structural analysis; Magneto-optic Kerr effect; Amorphous and nanocrystalline magnetic cores; Induced magnetic anisotropy
• ISSN: 0304-8853; 1873-4766
• DOI: 10.1016/j.jmmm.2017.07.055

•Thermal treatment under magnetic field develops a macroscopic magnetic anisotropy in amorphous Finemet alloy.•XRD paths reflect nanocrystalline character of thermal treated cores.•MOKE indicator film provides visualization of magnetic domain structure.
We report changes of coercivity, induced magnetic anisotropy, magneto-optical domain structure and frequency dependencies of coercivity and energy loss (up to 10MHz) associated with the structural modifications produced by thermal treatments under applied magnetic field (field annealing) in toroidal wound cores of Fe73.5Cu1Nb3Si15.5B7 amorphous alloy. The thermal treatment (535°C, 1h) leads to the typical nanocrystalline structure of α-Fe(Si) nanograins (60–65% relative volume, 10–20nm average grain size embedded in a residual amorphous matrix, while the magnetic field with the possibility to be applied in two directions to the toroidal core axis, that is in transverse (which is equivalent to the transverse direction of the ribbon) or longitudinal (equivalent to the longitudinal direction of the ribbon), develops a macroscopic uniaxial magnetic anisotropy in the transverse (around 245J/m3) or longitudinal (around 85J/m3) direction of the ribbon, respectively. It is remarkable the quasi-unhysteretic character of the cores with these two kinds of field annealing as comparing with that of the as-quenched one. Magneto-optical study by Kerr-effect of the ribbons provides useful information on the domain structure of the surface in agreement with the direction and intensity of the induced magnetic anisotropy. This induced uniaxial magnetic anisotropy plays a very important role on the Hc(f) and EL(f) curves, (f: frequency), being drastic the presence and direction of the induced magnetic anisotropy. In addition, these frequency dependencies show a significant change at the frequency around 100Hz.