Magnetoimpedance Studies on Metglas and Co/Fe Rich Nanocrystalline Ribbons

Magnetoimpedance(MI) is the significant change of the complex impedance of a soft ferromagnetic material upon the application of an external magnetic field. The thesis covers the, Fe/Co rich amorphous (METGLAS) and nanocrystalline (FINEMET & HITPERM) ribbons and thin films. The ribbons were prepared using melt-spun technique and thin films preparations were done employing DC magnetron sputtering. Different types of annealings viz., conventional-, Joule-and stress annealings were used. FINEMET family- [Fe73.5Si13.5B8CuV(3-x)AlNbx (x = 0, 1, 1.5, 3.0)] ribbons has been chosen for the MI studies. While the as-cast ribbon is amorphous in nature, α- FeSi nanoparticles are observed (in XRD) in the annealed ribbon. The particle sizes were determined from the TEM and they seem to increase with increasing V. Increase in the V content is seen to cause a sharp decrease in crystallization temperature.  This indicates that V plays a sensitive role in stabilizing the amorphous phase against nanocrystallization. Both contact and non-contact measurement was done for magnetoinductance (mi), MI and ACMR (acmagnetoresisatnce) measurement. Largest MI of the order of ~104% (largest MI ever obtained) was observed for x=1.0 ribbon. The resistivity was determined at room temperature. Transverse permeability plays a crucial role in the case of the contact method while it is the longitudinal permeability in the non-contact method.  In-plane anisotropy and other magnetic properties were studied using FMR. Presence of the transverse domains was confirmed by MFM studies. METGLAS family- This family [Co/Fe-Si-B/P-transition metalloid] exhibits excellent glass forming ability and low resistivity. On annealing, soft magnetic properties improved but no nanocrystalline phases were observed and grain size of 0.1-1 µm were observed on heating above 500oC. The values of MI, ACMR and mi for Co rich ribbons are larger in comparison with the Fe-rich ribbons. HITPERM family- Annealed HITPERM [(Fe,Co)-M-B-Cu ; M = Nb, Hf or Zr)] ribbons are reported to be  nanocrystalline containing α-FeCo and subsequently, to retain their soft magnetic properties up to very high temperatures (~800oC). Multiphases viz. fcc and hcp nanophases were observed on conventional annealing. Effect of different types of annealings on mi, MI and ACMR were studied for this family. MFM was employed to study domains. Co-RICH film-Structural compositional and surface morphology was done using XRD, EDAX and AFM. While in the as-deposited film, no MI was observed, MI of 2% was obtained after conventional annealing. MAGNETIC SENSOR- A magnetic sensor was made using FINEMET ribbon as the sensing element for detection of the horizontal component of the earth’s magnetic field.