E. Lopez

Magnetoelastic effects in amorphous Fe 40 Ni 40 P 14 B 6 alloys

The influence of compressive, tensile, and bending stresses on the magnetization processes, anisotropy energy, and remanence of an as-quenched amorphous Fe 40 Ni 40 P 14 B 6 ribbon has been studied. The magnetostriction constant has been obtained from the variation of the susceptibility with the applied compressive stress. To better understand the results, domain structures have been observed by using the Bitter technique. Our results show that the Metglas ribbon has a central region with compressive stress, while the edge regions have tensile stress. So, the influence of these regions on the magnetization processes will be very different according to the applied stress.

Flux-gate sensor based on planar technology

A fluxgate-like magnetometer using planar technology has been developed. The performance is comparable to conventional fluxgates. Due to minor inductive and capacitive effects of the planar coils, higher exciting frequencies can be used. >

Magnetostatic energy calculations in two- and three-dimensional arrays of ferromagnetic prisms

Exact analytic expressions for magnetostatic energy calculations in arrays of ferromagnetic prisms are presented. They apply to two-dimensional (2-D) and three-dimensional (3-D) arrays of variable length prisms with uniform magnetization inside each prism. This permits the study of irregular magnetic structures allowing also a variable grid where the size of the cells depends on the structure itself. These expressions cover all possible cases for 2-D and 3-D problems.

Study of the dynamic interaction of a domain wall with a pinning plane

The motion of a domain wall under the action of an alternating magnetic field was studied during its interaction with a pinning plane. First and second harmonics of the electronic force were measured by a lock-in amplifier, using a computer-controlled system. Good agreement was obtained between theory and experiment. Therefore, results of these experiments were used to determine the characteristics of the pinning place in the sample. The optimal frequency and amplitude of the exciting field have been investigated using this effect and have been used to develop a magnetic sensor. >

Reducing hysteresis in magnetostrictive-piezoelectric magnetic sensors

In this paper, we present a method to avoid hysteresis in magnetostrictive-piezoelectric sensors. It is based on the application of an alternating magnetic field of a frequency different than the piezoelectric exciting frequency that supplies enough energy to overcome any domain wall pinning. The signal is filtered with a notch filter synchronized to the magnetic field frequency and thus it does not contribute to the useful response of the sensor. The results show an appreciable decrease in the magnetic hysteresis and also a small decrease in the sensitivity of the sensor.

Local temperature in amorphous ribbons during current annealing

A study of the temperature dispersion during current-annealing of amorphous ribbons has been done. The local temperature has been obtained by measuring the local intensity of the infrared emission of the sample with a CCS nitrogen liquid cooled camera. The results exhibit a dispersion in the local temperature in spite of the small dimension of the sample. This study shows that the crystallization processes can be detected in situ through the mean square deviation of the infrared emission. >

Application of flash annealed amorphous ribbons in security systems

Flash annealing techniques have been used to crystallize locally amorphous materials and so to obtain samples that present alternatively soft and hard zones for application in magnetic labels for security systems. We show that by adequately controlling the local flash annealing, it is possible to obtain materials with different ratios between the first and third harmonic of the induced signal in a detecting coil that can be used to codify the magnetic labels. >

Application of domain wall stabilization to magnetic sensors

The influence of different stresses and annealing conditions is studied to improve the induced helical anisotropy. The possibility of developing a magnetic sensor based on the domain wall stabilization effect to detect low magnetic fields is pointed out. >

Temperature and stress effects on viscous damping parameter β of magnetic domain wall dynamics

Viscous damping parameter, β, and propatation field, H p , have been measured in Metglas 2826 ribbons under stress (from σ = 103 MPa to σ = 365 MPa) at different temperatures (from t = 25 °C to t = 200 °C) Results show that propagation field depends on domain wall energy, γ, at constant temperature. Viscous damping, β = β E + β R , (being β R relaxation damping and β E eddy current damping) depends on domain wall thickness, δ, and on parameter (μ o M s )2/ρ (ρ resistivity, μ o M s saturation magnetization) through β R and β E respectively.