FERROMAGNETIC NANOCOMPOSITES WITH TAILORED HYSTERESIS LOOP BY MAGNETIC AND TENSILE STRESS ANNEALING

Lajos Karoly Varga

   New, annealing time reducing technologies for heat treatments with and without magnetic field of amorphous precursor of soft magnetic nanocrystalline alloys will be presented for traditional Finemet alloy (Fe_73.5Si_15.5B₇Nb₃Cu₁). Small - scale thermal cycles with steadily increasing average temperatures can replace successfully the presently applied long term heat treatments with small heating velocity. In the case of continuous tensile stress annealing, the pulling velocity of ribbon can be increased up to 90 m/min which makes the productivity of this method competitive with the magnetic field annealing. The ultimate goal is to flatten the hysteresis loop on demand extending the linearity up to the induced anisotropy field value. The effective permea-bility can be decreased down to 20000 by applying transversal magnetic field annealing and further decrease down to 80 value can be obtained by applying tensile stress annealing up to 500 MPa. A properly conducted magnetic field annealing improves the coercive field below 1 A/m. The heterogeneities introduced by tensile stress annealing can be controlled to keep the coercive field below 10 A/m.

Keywords: amorphous magnetic materials, magnetic properties, perpendicular magnetic anisotropy, soft magnetic materials

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