Stress On Fecosib Amorphous Magnetic Flexible Thin-film Magnetic Properties

For the amorphous magnetoelastic films, owing to the absence ofmagnetocrystalline anisotropy and high magnetoelastic coupling coefficient, itsmacroscopic magnetic properties such as domain structure and magnetic properties et al,are largely determined by the stress-induced anisotropy. In this thesis, the influences ofstress on the magnetization process and magnetic properties of FeCoSiB amorphousmagnetoelastic film have been studied theoretically and experimentally.Theoretically, based on the Jiles-Atherton (J-A) model, the origins of the domainwall pinning in the domain displacement process have been analyzed and the domainrotation mechanism in the Stoner-Wolhfarth (S-W) model has been introduced to themodel according to the characteristics of amorphous magnetoelastic films. Thedependences of the pinning coefficient on the applied magnetic field and the externalstress have been studied. Finally, a domain wall pinning hysteresis loop model includingthe contribution of the applied stress has been established. Based on this model, thehysteresis loops of the tensile or compressive stressed amorphous magnetoelastic filmshave been simulated and the influences of the external stress on the hysteresis loop andcoercive has been discussed. The results show that the magnetization process and themagnetic properties strongly depend on the applied stress. When the stress is appliedalong the direction of the magnetic field, the coercive field decreases with the increasingof the tensile stress, and increases with the increasing of the compressive stress.Experimentally, FeCoSiB amorphous films are prepared on the glass substrateusing DC magnetron sputtering. The composition, hysteresis loop, surface morphologyand domain structure of the films prepared in different Ar pressures have beeninvestigated using EDAX, VSM, AFM and MFM respectively. The results show that thesputtering pressure influences not only the composition and surface morphology of thefilms, but also the hysteresis loops of the films. The domain structures of the filmsdepend intimately on the sputtering pressure. The magnetic contrast of the stripe domainincreases with the increasing of the Ar pressure.The tensile or compressive stressed FeCoSiB films are prepared using stress-growth technique. The effects of stress on the magnetic properties such asmagnetic anisotropy, remanence, coericivity and magnetic domain have been studied.The results show that strong magnetic anisotropy has been induced by applied stress,and the anisotropy field increases linearly with the increase of the applied stress. Whenthe films are tensile stressed, an easy axis is induced along the direction of the stress. Bycontraries, when the films are compressive stressed, an easy axis is inducedperpendicular to the direction of the stress. The hysteresis loops, coercive field and theremanence of the films are also influenced greatly by the applied stress, which isagreement with the simulation results qualitatively. The domain structures stronglydepend on the applied stress. With the increase of the tensile or compressive stress, thedivergence of the magnetic moment decreases and the domain structures transform fromirregular domains into parallel strip domain. While the tensile stress has been applied,the stripe domains align with the direction of the tensile stress. While the compressivestress has been applied, the stripe domains align perpendicular to the direction of thecompressive stress. The magnetic domain image disappears when the tensile stress isstrong enough.