Analysis of Electrodeposited NiFe Thin Films for the Development of Planar Fluxgate Magnetic Sensors
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0998-J05-21
Analysis of Electrodeposited NiFe Thin Films for the Development of Planar Fluxgate Magnetic Sensors Thais Cavalheri dos Santos, and Marcelo Mulato Departamento de Física e Matemática - FFCLRP, Universidade de São Paulo, Av. Bandeirantes 3900, Ribeirão Preto-SP, CA, 14040-901, Brazil
Abstract Nife alloys are potential candidates for the development of planar fluxgate magnetic microsensors. In this work, electrodeposition was used to produce NiFe thin films on top of copper substrates. When using this technique the variation of the electric potential, and thus the current density, alters the final stoichiometry of the deposited films, while the final thickness is determined by the total deposition time. We used current densities varying from 4.0 mA/cm2 to 28 mA/cm2, with steps of 4.0 mA/cm2. For each current density, total deposition times of 10, 20, 30 and 40 minutes were used. The morphology was characterized using scanning electron microscopy, structure was characterized using X-ray diffraction experiments, and the composition of the films were determined using energy dispersive spectroscopy. The magnetic properties were investigated evaluating the materials hysteresis cycle. The materials were optimized aiming for lowest coercivity values, and the final result was about 0.215 kA/m.
Introduction Fluxgates are part of a class of magnetic measurement devices. Basically, there is an induction of an electrical voltage in a sensor coil by the presence of time-variable magnetic field. The working principle of the fluxgate is the variation of the magnetic permeability of a ferromagnetic material, which in our case is a NiFe alloy, placed in the interior of the sensor coil [1]. The functioning of the fluxgate can be explained by the direct use of Faraday’s Law [2], which relates the induction of an electromotive force ε in the terminals of the coil, to the variation of the magnetic flux φ through it. The magnetic flux canalized in the interior of the sensor coil is directly proportional to the magnetic permeability of the ferromagnetic material which constitutes the coil nucleus. In this way, variations of the magnetic flux can be made through changes in the permeability of this material [3]. When applying a controlled variable magnetic field, the permeability of the nucleus can be modulated [1]. This variable magnetic field is called the excitation field, and is generated by a variable current passing through a second coil which also involves the ferromagnetic material. Without any external influence, the magnetic permeability of the material is set to an arbitrary value µ . During operation, the excitation coil can lead the core material to its maximum permeability value µ max [1]. The variation of the flux of the magnetic field inside the detection coil is given by [4]: ∆φ = ( µ 0 − µ max ) ⋅ N ⋅ A ⋅ H ext
(2)
where ( µ 0 - µ max ) is the difference between the permeability of the material in the two extreme conditions: before and after saturation. N is the number of loops of a coil and A is the transv
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