L. Gonzalez-Legarreta

Optimization of the giant magnetoimpedance effect of Finemet-type microwires through the nanocrystallization

We studied correlation of magnetic properties, giant magnetoimpedance (GMI) effect and structure of Finemet-type glass-coated microwires obtained by the Taylor-Ulitovski technique. We observed considerable magnetic softening and increasing of the GMI ratio, ΔZ/Z, (from 3% up to 100%) after annealing of studied microwires. On the other hand, even in as-prepared Fe73.8Cu1Nb3.1Si13B9.1 microwire, we observed existence of α-Fe nanocrystallites with average grain size about 12 nm and considerable GMI effect (ΔZ/Z up to 50%).

Effect of Nanocrystallization on Magnetic Properties and GMI Effect of Fe-rich Microwires

We studied the giant magnetoimpedance (GMI) effect and magnetic properties of Finemet-type FeCuNbSiB microwires. We observed that the GMI effect and magnetic softness of glass-coated microwires produced by the Taylor–Ulitovski technique can be tailored by controlling the magnetoelastic anisotropy of as-prepared FeCuNbSiB microwires, and can also be considerably improved either by heat treatment and/or choosing the suitable fabrication conditions. We observed a considerable magnetic softening of the microwires after the appropriate annealing. This magnetic softening correlates with the devitrification of amorphous samples. Amorphous Fe-rich microwires exhibited a low GMI effect (GMI ratio below 5%). A considerable enhancement of the GMI effect (GMI ratio up to 100%) has been observed in heat-treated microwires with nanocrystalline structure.

Effect of Nanocrystallization on Magnetic Properties and GMI Effect of Microwires

We studied giant magnetoimpedance (GMI) effect and magnetic properties of FINEMET-type FeCuNbSiB microwires. We observed that the GMI effect and magnetic softness of glass-coated microwires produced by the Taylor–Ulitovski technique can be tailored either controlling magnetoelastic anisotropy of as-prepared FeCuNbSiB microwires or controlling their structure by heat treatment or changing the fabrication conditions. We observed considerable magnetic softening of studied microwires after annealing. This magnetic softening correlates with the devitrification of amorphous samples. Amorphous microwires exhibited low GMI effect (GMI ratio below 5%). Considerable enhancement of the GMI effect (GMI ratio up to 100%) has been observed in heat treated microwires with nanocrystalline structure. Some of as-prepared Fe-rich exhibited nanocrystalline structure and the GMI ratio up to 45%.

Annealing Influence on the Exchange-Bias and Magnetostructural Properties in the Ni50.0Mn36.5Sn13.5 Ribbon-Shape Alloy

We report on the influence of short annealing treatments at 923 K and 1073 K during 10min on both martensitic transformation and exchange bias effect for the Ni50.0Mn36.5Sn13.5 Heusler alloy ribbon by means of magnetic measurements. We have observed that the martensitic transformation is shifted towards higher temperatures with increasing annealing temperature. Furthermore, isothermal M(H) hysteresis loops performed under field-cooling protocol show an exchange bias effect for as-quenched and two annealed ribbons, which indicates the existence of ferromagnetic-antiferromagnetic interactions at low temperatures. In particular, we observe that HC diminishes with the increasing of the annealing temperature, but HE is not affected by the heat treatment.

Induced Giant Magnetoimpedance Effect by Current Annealing in Ultra Thin Co-Based Amorphous Ribbons

We have studied the magnetoimpedance (MI) response of near-zero magnetostriction (Co0.95Fe0.05)75Si10B15 (Co-based) amorphous ribbons (0.50 mm wide, 32 μm thick), thermally treated by current annealing, for different dc current of intensity varying from 440-680 mA during 5 min, was investigated in the frequency range of 10 MHz-1 GHz. It was not observed MI effect in the as-quenched ribbon, while the current annealed ribbons display large MI depending on the current annealing intensity in a similar way to that of the inhomogeneous induced magnetic anisotropy developed by this peculiar thermal treatment.

Crystalline structure and magnetic behavior of the Ni41Mn39In12Co8 alloy demonstrating giant magnetocaloric effect

Magnetic cooling is a green cooling technology, which is more energy efficient than existing fluid-compression cooling machines. Ni41Mn39In12Co8 alloy, which demonstrates promising magnetocaloric performances, was investigated using neutron diffraction and thermomagnetic measurements. The austenite structure is cubic L-21 (Fm (3) over barm), while that of the martensite is a mix of 8 and 6 M modulated monoclinic structures (P 12/m 1). The austenitic site occupancy refinements reveal that all substituting Co atoms occupy Ni-sites. Most Mn atoms (65%) are in the Mn-sites and the rest go to In-sites (about 35%) and Ni-sites (less than 5%). This disorder of the magnetic atoms (Mn, Ni and Co) in the austenitic phase remains unchanged during the martensitic transition. The distortions of the interatomic distances due to the modulation of the martensitic structures further enhance the disorder in the magnetic interactions. Thermomagnetic measurements indicate that the austenitic phase is ferromagnetic. Cooling to below 250 K, where the alloy loses its ferromagnetic nature, and down to 50 K, the lack of any antiferromagnetic Bragg peaks suggests no antiferromagnetic ordering in the martensitic phase. At very low temperatures in the martensitic phase, spin glass magnetic nature is identified by magnetic measurements, and the spin-glass transition temperature is similar to 19 K.

Magnetic and Magneto-Optical Research of Ni43.7Mn43.6In12.7 Ribbons

We report the magnetic and magneto-optical (MO) properties of the Heusler Ni43.7Mn43.6In12.7 alloy ribbon in martensitic and austenitic states. The samples were produced by rapid solidification using the melt-spinning technique. The difference between the transformation temperatures obtained from magnetization and transverse Kerr effect (TKE) measurements shows that the chemical composition and/or microstructure are not identical in the bulk and at the ribbon surface. The TKE spectra profile in the spectral energy range of 0.5-3.5 eV does not change significantly at the martensitic transformation that indicates on a very similar electronic structure in martensitic and austenitic states.

Tailoring of Soft Magnetic Properties and High Frequency Giant Magnetoimpedance in Amorphous Ribbons

Soft ferromagnetic amorphous ribbons attract a considerable attention for their applications as high-performance sensing elements in different giant magnetoimpedance (GMI)-based magnetic sensors to measure magnetic field, current, and stress with high sensitivity and better signal to noise ratio than magnetic sensors based in other effects. GMI is mainly determined by the ribbon transverse permeability and this parameter can be suitable enhanced by inducing a magnetic anisotropy by different thermal treatments in amorphous ribbons. In this chapter we report studies on the analysis of GMI response of near-zero magnetostriction Co-based amorphous ribbons exhibiting a macroscopic uniaxial magnetic anisotropy induced by two kinds of thermal treatment, namely: by current annealing (440–680 mA during 5 min) and by stress-annealing treatment (300 MPa applied tensile stress at different temperature, i.e., 340, 360, and 400 °C, during 1 h) in the frequency range from 100 MHz up to 3500 MHz. Comparison among GMI effect of stress-annealed and current-annealed ribbons is discussed.

Giant Magnetoimpedance Effect of Amorphous and Nanocrystalline Glass-Coated Microwires

In this chapter we are reporting on correlation of Giant magnetoimpedance (GMI) effect and magnetic properties of amorphous and nanocrystalline Co-Fe rich glass-coated microwires. We measured the GMI magnetic field, frequency dependences and hysteresis loops of composite microwires produced by the Taylor-Ulitovsky technique. We observed that GMI effect and magnetic softness of glass-coated microwires produced by the Taylor-Ulitovsky technique can be tailored either controlling magnetoelastic anisotropy of as-prepared microwires or controlling their internal stresses and structure by heat treatment. High GMI effect has been observed in as-prepared and annealed Co-rich microwires. In the case of Fe-rich Finemet-type microwires we observed considerable magnetic softening of studied microwires after annealing. This magnetic softening correlates with the devitrification of amorphous samples. Amorphous Fe-rich microwires generally exhibited low GMI effect (GMI ratio below 5 %). Considerable enhancement of the GMI effect (GMI ratio up to 100 %) has been observed in heat treated microwires with nanocrystalline structure. The objective of this reported work is to develop magnetically soft thin wires for applications in magnetic field sensors.

Magnetotransport at High Frequency of Soft Magnetic Amorphous Ribbons

Magnetic properties of amorphous alloy ribbons have been extensively studied for nearly a quarter of a century since their first production. Much interest in these materials has been stimulated by their remarkable magnetomechanical and magnetotransport properties. It is amazing to notice with respect to the so-called giant magnetoimpedance effect (GMI) effect that the rapid advantages in the understanding of the underlying physical mechanisms of GMI have allowed the development of practical devices and applications using this effect. Therefore, the large influence of magnetic fields and also mechanical stresses in determining the magnetic permeability and electrical impedance of such soft ferromagnetic alloys make these materials very suitable for sensing magnetic field, current and stress. In this chapter we will try to report the recent studies on GMI response of near-zero magnetostriction Co-based amorphous ribbons in as-cast (with different wide dimension) state, and exhibiting a macroscopic uniaxial magnetic anisotropy induced by different stress-annealing treatment (300 MPa applied tensile stress at different temperature i.e., 340, 360, and 400 oC, during 1 h) in the frequency range from 10 MHz up to 1000 MHz. Comparison among GMI effect of as-cast state and stress-annealed ribbons will be discussed. It is remarkable that a more spectacular and defined GMI effect is observed in the stress-annealed ribbons owing to the presence of a macroscopic uniaxial transverse magnetic anisotropy developed with the stress-annealing treatment that enhances the transverse component of the magnetic susceptibility.