Nguyen Hoang Nghi

Influence of Fe doping and FeNi-layer thickness on the magnetic properties and GMI effect of electrodeposited Ni100−xFex/Cu (x = 0–95) wires

A systematic study has been performed by the influence of Fe doping and FeNi-layer thickness on the giant magnetoimpedance (GMI) effect of electrodeposited Ni100−xFex/Cu (x = 0–95) composite wires. Results obtained show that there is a correlation between the structure, soft magnetic properties and the GMI effect. Among the compositions investigated, the largest MI ratio is achieved for Ni44Fe56/Cu as a result of it having the softest magnetic property (i.e. the lowest coercivity), which arises from the smallest nanograin size. As the NiFe-layer thickness (t) increases from 1 to 27.4 µm, the GMI ratio initially increases, reaches a maximum of 110% at t = 27.4 µm and then decreases for t > 27.4 µm. Interestingly, GMI curves show a single-peak feature for wires with t < 20 µm, but a double-peak one for wires with t ≥ 20 µm. This indicates that there is a formation of a circular domain structure with a well-defined circumferential anisotropy in the NiFe magnetic layer of the wires with t ≥ 20 µm. This in turn results in a great improvement in the GMI effect of these wires.

Magnetoelectric effects in piezoelectric/soft magnetic amorphous FeCo-based ribbon composites

Magnetoelectric effect has been investigated in several multiferroic laminates generated by inserting a lead-zirconate titanate PZT plate between sheets of highly soft magnetic amorphous FeCo-based alloy ribbon. The results show that the magnetoelectric coefficient αE (= dE/dH) depends on the rest glass-forming elements as well as the concentration of Co substitution. Giant magnetoelectric is found for the composite of Fe73.5Cu1Nb3B9Si13.5 ribbon, where αE as high as 1000 mV/cmOe at low field of 50 Oe. aE can be further improved up to 1170 mV/cmOe at 20% Fe substituted by Co. The higher the Co concentration, the lower magnetoelectric effect is observed. High magnetoelectricty at low field makes these composites suitable for special applications such as smart sensors for detecting microtesla magnetic fields and especially biosensor for magnetic label detection.

Magnetic and sensitive magnetoelastic properties of Finemet nanostructured ribbon

Soft-magnetic Fe73.5Cu1Nb3Si13.5B9 (Finemet) ribbon has been fabricated by using melt-spinning techniques. After annealing at suitable temperature the ribbon changes from an amorphous to crystalline state which related to the formation of Fe nanocrystallites. Study on the magnetic and magnetoelastic properties of the ribbon is presented. Furthermore, based on the fabricated ribbon stress sensors are simply constructed. The sensors showed high sensitivity of 3.8 mV/MPa as well as a wide working range up to 17 MPa. These sensors are potential for practical applications such as detecting small stress and movement in civil structures.

Advanced Metallic Magnetic Materials Prepared by Electro-Chemical Deposition, Vapor Deposition and Rapid Quenching

By use of Electro-Chemical, Vapor Deposition and Rapid Quenching (RQ) techniques several magnetic materials in the form of thin layers are manufactured and investigated. These, generally, nano sized and multiphase, 3d-based materials exhibit a series of properties and effects such as Giant-Magneto Resistance (GMR) and Giant-Magneto Impedance (GMI) effects depending on their composition. The results of long-standing research in the Hanoi University of Technology on preparation technology, structure, properties and application of this kind of materials are shown and discussed in terms of their practical use.