Exchange Coupling And Magnetic Dipole Interactions In FINEMET Composite Ribbons

Exchange coupling and magnetic dipole interactions play an important role in the origin of magnetism as well as the basic research and applications of magnetic materials,which attracts extensive attention in condensed matter physics in recent years.The magnetic properties of soft magnetic materials as a magnetically sensitive element,are often affected by exchange coupling and magnetic dipole interactions in the presence of other magnetic materials in the proximity.The degree of influence of these two magnetic interactions on the magnetic properties of the material is clarified and utilized,which is helpful to improve the soft magnetic properties of materials and to design highly sensitive sensors.Therefore,in this paper,the nanocrystalline(FINEMET)composite ribbons with different film structures were prepared by magnetron sputtering.The movement of the peak position field(magnetic field corresponding to the maximum impedance)and the change of the bias field(magnetic field corresponding to the minimum impedance at the weak field)of the magneto-impedance curves were analyzed by using the giant magnetoimpedance effect,and the two magnetic interactions were separated.The main research contents and conclusions are as follows:1.Exchange coupling and magnetic dipole interactions between Fe₅₀Pd₅₀magnetic layer and FINEMET ribbon.(1)In the FINEMET/Fe₅₀Pd₅₀composite ribbons,Magneto-optical Kerr microscopy confirms that the FINEMET ribbon and Fe₅₀Pd₅₀film have transverse and longitudinal magnetic structures,respectively.The measurement of magnetic impedance shows that the magnetic impedance curves are asymmetric due to the bias field generated by Fe₅₀Pd₅₀film on FINEMET ribbon.The bias field decreases from0.8 Oe to 0.3 Oe with the increase of the thickness of Fe₅₀Pd₅₀film.The exchange coupling and the magnetic dipole interactions are separated by analyzing the change of the peak position field of the magneto-impedance curves.When the thickness of Fe₅₀Pd₅₀film is 55 nm,the exchange field is equal to the dipole field.When the thickness of Fe₅₀Pd₅₀film is less than 55 nm,the exchange field generated by Fe₅₀Pd₅₀film on FINEMET ribbon dominates the change of peak position field.The dipole field generated by Fe₅₀Pd₅₀film on FINEMET ribbon dominates the change of peak position field when the thickness of Fe₅₀Pd₅₀film is greater than 55 nm.(2)In the FINEMET/SiO₂/Fe₅₀Pd₅₀composite ribbons,the bias field generated by Fe₅₀Pd₅₀film on the FINEMET ribbon results in asymmetrical magneto-impedance curves,and the bias field comes from the dipole field generated by the Fe₅₀Pd₅₀film on the FINEMET ribbon.Compared with the FINEMET/Fe₅₀Pd₅₀composite ribbons,the presence of SiO₂weakens the dipole field generated by Fe₅₀Pd₅₀film on the FINEMET ribbon,resulting in the decrease of the bias field of FINEMET/SiO₂/Fe₅₀Pd₅₀composite ribbons.(3)In the Fe₅₀Pd₅₀/FINEMET/Fe₅₀Pd₅₀composite ribbons,the dipole field produced by Fe₅₀Pd₅₀film on FINEMET ribbon weakens with the increases of Fe₅₀Pd₅₀film thickness,which results in the decrease of bias field and the asymmetry of magnetic impedance curves.Relative to the FINEMET/Fe₅₀Pd₅₀composite ribbons,the lower Fe₅₀Pd₅₀film generates a dipole field on the upper surface of the FINEMET ribbon,which increases the dipole field of the Fe₅₀Pd₅₀/FINEMET/Fe₅₀Pd₅₀composite ribbons.2.Exchange coupling and magnetic dipole interactions between Fe₅₀Pt₅₀magnetic layer and FINEMET ribbon.(1)In the FINEMET/Fe₅₀Pt₅₀composite ribbons,Magneto-optical Kerr microscopy confirms that the Fe₅₀Pt₅₀film and the FINEMET ribbon have transverse magnetic structures.The measurement of magnetic impedance indicates that the magnetic impedance curves of the composite ribbons show symmetrical characteristics.By analyzing the change of the peak position field of the magneto-impedance curves and combining with the magnetic-dipole interaction model,it is concluded that the exchange field is equal to the dipole field when the distance r between the middle of Fe₅₀Pt₅₀film and the surface of the FINEMET ribbon is 40 nm.When r is less than 40 nm,the exchange field generated by Fe₅₀Pt₅₀film on FINEMET ribbon dominates the variation of peak position field.The dipole field produced by Fe₅₀Pt₅₀film on FINEMET ribbon dominates the change of peak position field when r is greater than 40 nm.(2)In the FINEMET/SiO₂/Fe₅₀Pt₅₀composite ribbons,the dipole field produced by Fe₅₀Pt₅₀film on FINEMET ribbon decreases from 0.4 Oe to 0.1 Oe when the thickness of SiO₂increases from 10 nm to 100 nm.Compared with the FINEMET/Fe₅₀Pt₅₀composite ribbons,the presence of SiO₂weakens the dipole field generated by the Fe₅₀Pt₅₀film on the FINEMET ribbon and reduces the peak position field of the FINEMET/SiO₂/Fe₅₀Pt₅₀composite ribbons.3.Exchange coupling and magnetic dipole interactions between double magnetic layers and FINEMET ribbon.(1)In the FINEMET/Fe₅₀Pt₅₀/Fe₅₀Pd₅₀composite ribbons,the bias field of Fe₅₀Pd₅₀and Fe₅₀Pt₅₀film on FINEMET ribbon leads to asymmetrical magnetic impedance curves.When the thickness of Fe₅₀Pt₅₀film is small,the exchange field produced by Fe₅₀Pt₅₀film on FINEMET ribbon,and the dipole field produced by Fe₅₀Pt₅₀and Fe₅₀Pd₅₀film on FINEMET ribbon affect the change of peak position field.The exchange field produced by Fe₅₀Pt₅₀film on FINEMET ribbon,and the dipole field produced by Fe₅₀Pt₅₀and Fe₅₀Pd₅₀film on FINEMET ribbon weakens with the increases of Fe₅₀Pt₅₀film thickness,thus the peak position field falls from 4.6Oe to 2.6 Oe.(2)Compared with the FINEMET/Fe₅₀Pt₅₀composite ribbons,Fe₅₀Pt₅₀and Fe₅₀Pd₅₀films generate dipole fields for FINEMET ribbon respectively,which increases the peak position field of FINEMET/Fe₅₀Pt₅₀/Fe₅₀Pd₅₀composite ribbons.Compared with the FINEMET/Fe₅₀Pd₅₀composite ribbons,the presence of the Fe₅₀Pt₅₀film weakens the dipole field generated by the Fe₅₀Pd₅₀film on the FINEMET ribbon,which reduces the bias field of the FINEMET/Fe₅₀Pt₅₀/Fe₅₀Pd₅₀composite ribbons.