H. García-Miquel

Very large magnetoimpedance effect in FeCoNi ferromagnetic tubes with high order magnetic anisotropy

The extraordinarily high (up to 800% magnetoimpedance ratio) and sensitive magnetoimpedance effect has been found and studied in FeCoNi magnetic tubes electroplated onto CuBe nonmagnetic wire at frequency of about 1 MHz order. Special annealing was done in order to induce magnetic anisotropy. The high harmonic response has been studied, and the harmonics show larger variations with the external magnetic field than the fundamental. This huge sensitivity of the harmonics (up to an order of the tens of thousands %/Oe) is promising in regard to the increase of the sensitivity of giant magnetoimpedance sensors. To explain the experiment results, we calculated the high frequency transverse susceptibility taking into account the magnetic anisotropy of first and second orders. The susceptibility is extremely high at the points of orientational phase transitions in the magnetic layer which gives rise to strong nonlinear effects.

Domain wall propagation in bistable amorphous wires

Magnetostrictive Fe-base amorphous wires spontaneously exhibit square-shaped hysteresis loops that is characterized by a single quite large Barkhausen jump when the switching magnetic field is reached. This jump is ascribed to the propagation of a wall along the wire. In this paper, deeper information is reported on the propagation characteristics in these wires as a function of the amplitude and the frequency of the magnetic field generating such propagation. In particular, the wall velocity and its length are experimentally determined and the results are analysed considering the quasi-planar shape model for the wall that has been introduced recently, whose validity is confirmed.

Surface magnetic anisotropy in glass-coated amorphous microwires as determined from ferromagnetic resonance measurements

The ferromagnetic resonance frequency of different Co base glass-coated amorphous magnetic microwires about 3.5 μm in diameter with negative, vanishing and positive magnetostriction has been investigated from power absorption measurements in the microwave frequency range. The experimental technique employed here involves the replacement of the dielectric of a coaxial transmission line by the sample to be measured. From the evolution of the resonance frequency with DC applied magnetic field, the surface magnetic anisotropy field of the microwires has been quantitatively obtained and, as expected, found to depend on the sign and strength of the magnetostriction. Similar values for the surface anisotropy are obtained in comparison with bulk anisotropy as determined from quasi-static hysteresis loops measurements.

Modulation of electromagnic waves by alternating currents through left-handed ferromagnetic microwires

We present experimental results of electromagnetic wave modulation by the application of AC currents along a ferromagnetic microwire at the frequency range where left-handed transmission is observed. It is demonstrated that transmitted microwave signals through a waveguide mount are modulated by the current applied to the wire. From the measurements, we have extracted information about the magnetic susceptibility behavior of the microwires.

KLT-Based Interrogation Technique for FBG Multiplexed Sensor Tracking

The Karhunen–Loeve transform (KLT) is used to retrieve the wavelength information of several fiber Bragg gratings (FBGs) that are acting as a multiplexed sensor. The modulated light of a broadband source is launched to the FBG cascade in order to capture the electrical frequency response of the system. Thanks to dispersive media, the wavelengths of the FBGs are mapped in radio-frequency delays. Wavelength changes are determined by the amplitude change of the samples in the impulse response, a change which is followed by the eigenvalue calculated by the KLT routine. The use of the KLT routine reduces by three orders of magnitude the amount of points needed to have a subdegree resolution in temperature sensing, while keeping the accuracy almost intact.

Circular Magnetization Processes in CoFeNi Electroplated Wires

Circular magnetization processes in electroplated wires is an important topic having straight connection with sensor applications of these soft magnetic materials. In present work the longitudinal and circular hysteresis loops were measured and corresponding magnetization processes were studied in Cu98Be2/Co16Fe20Ni64 wires. The longitudinal hysteresis loops, Mz-Hz, were measured by inductive technique in a frequency range of 10 to 70 Hz. The circular magnetization curves (Mφ- Hφ) were measured for frequencies of 50 and 100 kHz in the Hφ field up to 1500A/m for different values of the axial external field of 0 to 500 A/m. The longitudinal and circular magnetization curves are comparatively analyzed.

Magneto-optical sensor based on fiber Bragg gratings and a magnetostrictive material.

We have designed a magneto-optical sensor based on fiber Bragg grating (FBG) and Metglas 2605CO (Fe67Co18B14Si1) material with magnetostriction coefficient of 35ppm. The FBG sensor is glued between two sheets of Metglas. FBG-based detectors are sensitive to both temperature changes (approximately 10pm/°C) and mechanical stress (approx. 1.15pm). Also due to the thermal expansion of Metglas, it becomes imperative to isolate the joint effects of thermal expansion of Metglas and the FBG temperature drifts. This is achieved by introducing an additional FBG used as a temperature sensor. We have characterized the responses of the sensor in two directions simultaneously: parallel and perpendicular to the direction of the applied magnetic field.

Magnetic Field Sensor Based on Giant Magnetoimpedance

Giant magnetoimpedance (GMI) effect has been studied in amorphous magnetic microwires where internal mechanical stresses derived from fabrication process influence strongly in its magnetic properties. Glass covered amorphous microwire of composition (Fe6Co94)72.5Si12.5B15 have been characterized in low magnetic DC field, for AC currents from 75 to 500 muA and frequencies from 1 to 14MHz. In all measurements a double peak response, characteristic of Co-rich samples with circular anisotropy, was obtained and GMI of 99% was reached. The design of a high sensitive magnetic field sensor has been made obtaining a linear response in plusmn130 A/m range with two microwires with the appropriate bias magnetic field.