Influence Of Magnetron Sputtering Techniques On The Micro Structure And Giant Magneto-impedance Effect Of The Composite Wires

The Giant Magneto-Impedance(GMI)effect consists of significant changes of the complex impedance value of soft magnetic materials upon the application of an external magnetic field.The phenomenon has attracted much attention over the past years because of its potential applications in magnetic recording heads and sensitive sensors,which are characterized by high sensitivity and quick response.In recent years,the research on GMI effect has extended to composites structure materials, which have shown enhancement of GMI effect compared with homogeneous materials.In this paper,the magnetron sputtering method is used to prepare composite wires.By varying the preparation techniques,the magnetic structure of the deposited layers can be controlled during deposition.This thesis includes studies on the structure and GMI effect of composite wires prepared by the following methods:1.Ni₈₀Fe₂₀/Cu composite wires were prepared by alternating the rotating direction of the wire during RF magnetron sputtering.In order to keep the overall coating thickness of all the samples constant,the alternating interval and the rotating period of each sample during sputtering were varied.As the rotating period increased, the deposited magnetic layers increased and the single layer thickness decreased.The results demonstrated that:(1)The composite wires prepared by the alternate rotating method show magnetic competing among layers.The magnetic behavior is the result of the overall magnetic competition.For samples with odd magnetic layers,there is a preferential orientation when being magnetized.The preferential orientation becomes weak as the layers increase.For samples with even magnetic layers,as the alternating interval changes,their magnetic structure varies and the samples show different magneto-impedance profiles.(2)There is a critical thickness for single sputtered layer at which the MI effect of the composite wire is significantly enhanced and could be observed at a relatively low driven current frequency.For an alternate rotational prepared Ni₈₀Fe₂₀/Cu composite wire with 24 magnetic layers and with a single layer thickness of 150 nm, the maximum GMI ratio of 240%has been achieved.Below the critical thickness,as the alternate rotating period increases,interface effect becomes important and its GMI effect decreases.2.Magnetron sputtering in the form of continuous deposition and intermittent deposition modes were used to obtain Ni₈₀Fe₂₀/Cu composite wires.The results show that intermittent deposition mode led to the formation of an interface between deposited layers.A better crystallite and a little grain growth were found for the intermittently deposited wires.The GMI profile for the intermittently deposited composite wire was characterized by two peaks.This phenomenon could be attributed to the presence of an interface between the deposited magnetic layers and the difference in the magnetic properties of the inner and the outer magnetic layers.As the intermittent times increases,the GMI effect of the composite wire decreases. Annealing was introduced to the intermittently deposited wire so that the inherent stresses were partially relaxed.As a result,its GMI effect was enhanced and the magnetic properties of the two magnetic layers became similar.3.The GMI effect of the bi-layer composite wires containing Ni₈₀Fe₂₀and Fe_73.5Cu₁Nb₃Si_13.5B₉ magnetic materials has been studied:(1)The Fe_73.5Cu₁Nb₃Si_13.5B₉ additional layer could change the stress distribution in composite wires.As the thickness of Fe_73.5Cu₁Nb₃Si_13.5B₉ layer increased,the internal stress increased in the Fe_73.5Cu₁Nb₃Si_13.5B₉/Ni₈₀Fe₂₀/Cu composite wire and the contribution of magnetoelastic anisotropy to the overall magnetic anisotropy increased.Thus,the value of anisotropy field of the composite wire increased.(2)The position of Ni₈₀Fe₂₀and Fe_73.5Cu₁Nb₃Si_13.5B₉ can influence the magnetic behaviors of the composite wires,and hence affect its GMI effect.The composite wire with Ni₈₀Fe₂₀as the inner layer shows positive MI effect,while the one with Fe_73.5Cu₁Nb₃Si_13.5B₉ as the inner layer shows minus MI effect.