Fe-rich Microwires Research Articles

Stress-Induced Magnetic Anisotropy Enabling Engineering of Magnetic Softness and GMI Effect of Amorphous Microwires

Stress-annealing enabled a considerable improvement in the GMI effect in both Fe- and Co-rich glass-coated microwires. Additionally, a remarkable magnetic softening can be achieved in stress-annealed Fe-rich microwires. Observed stress-annealing induced magnetic anisotropy is affected by annealing conditions (temperatures and stresses applied during annealing). The highest GMI ratio up to 310% was obtained in stress-annealed Co-rich microwires, although they presented rectangular hysteresis loops. A remarkable magnetic softness and improved GMI ratio over a wide frequency range were obtained in stress-annealed Fe-rich microwires. Irregular magnetic field dependence observed for some stress-annealing conditions is attributed to the contribution of both the inner axially magnetized core and outer shell, with transverse magnetic anisotropy.

Soft magnetic microwires for sensor applications

We provide an overview of the routes allowing the optimization of magnetic softness, giant magnetoimpedance (GMI) effect and domain wall dynamics in one of the families of magnetic microwires: glass –coated microwires prepared using Taylor-Ulitovsky method. The magnetic properties of as-prepared microwires are determined mostly by the magnetoelastic anisotropy. Conventional annealing allows a considerable improvement of the domain wall dynamics in Fe-rich microwires and a slight decrease of the coercivity, however, remarkable magnetic hardening is observed after conventional furnace annealing of Co-rich microwires. Stress annealing of Fe-rich microwires allows a considerable magnetic softening and GMI effect enhancement and even more remarkable improvement of the domain wall dynamics. In Co-rich microwires stress-annealing allows the improvement of GMI effect and even the induction of transverse magnetic anisotropy at high enough annealing temperature. However, the highest GMI effect is observed for stress-annealed Co-rich microwires which present rectangular hysteresis loops. Consequently, annealed Co-rich microwires can present both, fast domain wall propagation and GMI effect.Observed induced anisotropy and related changes of the magnetic properties are discussed considering the internal stresses relaxation, “back-stresses” and circumferential magnetic field during proposed post-processing.Consequently, correctly designed post-processing enabled us to design the magnetic anisotropy distribution beneficial for the optimization of the GMI effect and the domain wall dynamics in magnetic microwires.

Time-resolved motion of a single domain wall controlled by a local tunable barrier

We report on the time-resolved dynamics of a single magnetic domain wall (DW) under the influence of a tunable barrier in a Fe-rich microwire. The energy barrier was created by applying a local magnetic field antiparallel to the uniform driving field used to depin and propagate the DW along the wire. This originates the braking and eventually the trapping of the DW depending on the magnitude of the antiparallel local field. The motion of the DW through the local field becomes stochastic for minimum magnetic field values close to the measured friction field (Hfr = 24.4 A/m). This phenomenon is caused by fluctuations in the pinning field associated to the different types of local defects and residual stress existing in the wire. The probability for the DW to overcome the barrier has been estimated for different values of the local field. When the minimum applied field is lower than the fluctuating friction field the DW is always trapped.

Fine tuning of domain helical structure in magnetic microwires

We demonstrate that the tuning of magnetic domain structures in Fe-rich amorphous microwires can be engineered by the torsion stress and the circular magnetic field. Their co-directed or opposite action allows for fine tuning of domain structures with helical magnetization state. Also the effect of torsion stress induced reversible transition between spiral and elliptical domain structures has been discovered. The modeling of the stress and the circular magnetic field induced transformation of helical domain structure is in good agreement with the experimental results.

Giant magnetoimpedance in rapidly quenched materials

We present an overview of the factors as well as post processing tools allowing optimization of magnetic softness and GMI effect of rapidly quenched materials: microwires and ribbons. Generally, low coercivity and high GMI effect have been observed in as-prepared Co-rich compositions. Annealing at adequate conditions can be very effective for manipulation of the magnetic properties and GMI effect of amorphous and nanocrystalline rapidly quenched materials. After annealing of Co-rich compositions, we can observe transformation of inclined hysteresis loops to rectangular. However, at certain annealing conditions GMI effect can be improved. Using stress-annealing, GMI effect of both Fe-rich and Co-rich microwires as well as of amorphous ribbons can be improved. On the other hand, in Fe-rich FeCuNbSiB microwires after appropriate annealing we observed considerable magnetic softening and GMI effect enhancement. The other promising post-processing allowing GMI effect optimization is Joule heating.

High frequency giant magnetoimpedance effect of a stress-annealed Fe-rich glass-coated microwire

Processing by stress-annealing (450 MPa, 300 °C, 1 h) the glass-coated microwire of Fe75B9Si12C4 composition a macroscopic magnetic anisotropy with a circular component is developed. This anisotropy very significantly improves the giant magnetoimpedance (GMI) effect with respect to the observed in the as-prepared microwire. The analysis of the GMI response as a function of the frequency (10–1000 MHz) opens new lights to understand the distribution of the magnetic anisotropy inside the glass-coated microwire.We have investigated the GMI response of the stress-annealed Fe75B9Si12C4 glass-coated microwire. From the frequency dependence of the GMI we have analyzed the distribution of the magnetic anisotropy inside the metallic nucleus obtaining good agreement with the average value of the anisotropy field deduced from the hysteresis loop of the bulk.From measured magnetic field dependences of GMI ratio we evaluated the frequency and magnetic field dependences of the penetration depth. We found that the minimum penetration depth of Fe75B9Si12C4 microwire decreases from about 1.5 μm down to 0.8 μm after stress annealing.Obtained dependences demonstrate that the minimum penetration depth value as well as the frequency and magnetic field dependences are considerably affected by the stress-annealing.

Stress dependence of the magnetic properties of glass-coated amorphous microwires

We studied the effect of applied tensile stresses on magnetic properties of Fe- and Co-rich amorphous glass-coated microwires. Rising of magnetic anisotropy field upon tensile stress in Co-rich glass-coated microwires is described by a linear dependence. Furthermore, decrease of magnetic susceptibility upon tensile stress is observed in Co-rich microwires. A monotonous increase in the coercivity and the switching field upon tensile applied stress is observed for as-prepared Fe-rich microwire. Stress induced magnetic bistability consisting of transformation of hysteresis and onset of rectangular hysteresis loop upon tensile stress, σ, of about 22.5 MPa is observed in stress-annealed Fe-rich microwires. Such stress-induced magnetic bistability results in considerable growing of coercivity and remanent magnetization in stress-annealed Fe-rich microwires. The rising in the coercivity and the switching field upon applied tensile stresses in stress-annealed Fe-rich microwires with stress induced magnetic bistability (at σ > 22.5 MPa) is roughly described by the σ½ dependence, as previously reported for the wires with spontaneous magnetic bistability. Consequently, stress-annealing of Fe-rich microwire allows beneficial enhancement of the stress dependence of coercivity. Observed dependencies are discussed considering stress dependence of the magnetostriction coefficient in Co-rich glass-coated microwires, internal stresses redistribution and domain structure rearrangement in stress-annealed Fe-rich microwires upon applied tensile stresses.

Magnetic properties of “thick” glass-coated Fe-rich microwires

We report on preparation and magnetic properties of Fe71.7B13.4Si11Nb3Ni0.9 glass-coated microwire with metallic nucleus diameter d = 103 μm and total diameter D = 158 μm prepared by Taylor-Ulitovsky method. Amorphous structure of as-prepared microwires is confirmed by X-ray diffraction. As-prepared glass-coated microwires present relatively high GMI effect (about 50%) and relatively low coercivity (about 25 A/m). Additionally, as-prepared sample present rectangular hysteresis loop and fast single domain wall propagation with domain wall mobility of about 11,9 m2/As. After annealing we observed considerable improvement of the GMI ratio (from 50% up to 100%). Observed GMI effect improvement has been attributed to the stresses relaxation. From aforementioned studies we can conclude that the Taylor-Ulitovsky technique allows us to obtain thick ferromagnetic microwires with good magnetic properties and GMI effect suitable for industrial applications.

Smart composites with embedded magnetic microwire inclusions allowing non-contact stresses and temperature monitoring

A novel sensing technique for non-destructive and non-contact monitoring of the composites utilizing ferromagnetic glass-coated microwire inclusions with magnetic properties sensitive to tensile stress and temperature is proposed. We provide in-situ studies of the evolution of the hysteresis loop of arrays consisting of Co- and Fe-rich microwires, as well as transmission and reflection parameters of the composites with microwire inclusions during the composites matrix polymerization. We observed remarkable change of the hysteresis loops upon matrix polymerization: remarkable coercivity change and transformation of linear hysteresis loop to rectangular or from rectangular to linear for arrays with Co-rich and Re-rich microwires respectively. Using the free space technique we observed considerable variation of the reflection in the range of 4–7 GHz and transmission upon the matrix polymerization. Observed dependencies are discussed considering variation of temperature and stresses during the thermoset matrix polymerization and their influence on magnetic properties of glass-coated microwires.

Engineering of Magnetic Properties of Fe-Rich Microwires by Stress Annealing

We present our experimental results on optimization of the magnetic softness in Fe-rich magnetic microwires by stress annealing. It is found that the magnetic softness and magnetoimpedance effect of the Fe-rich microwires can be considerably improved by annealing. The hysteretic properties and magnetoimpedance are considerably affected by the tensile stress applied during the annealing. Experimental dependencies are attributed to changes in magnetic domain structure of magnetic wires in particular decrease of the inner axially magnetized core volume in expense of increase of the outer domain shell with transverse magnetization orientation. Observed stress-induced anisotropy and related changes of magnetic properties are discussed considering internal stresses relaxation and “back-stresses.”

Grading the magnetic anisotropy and engineering the domain wall dynamics in Fe-rich microwires by stress-annealing

We have studied the magnetic properties and domain wall dynamics in Fe-rich microwires subjected to stress-annealing. The hysteresis loops of Fe-rich microwires were considerably affected by stress-annealing. We obtained drastic decrease in coercivity and change in the character of hysteresis loops from rectangular to linear in stress-annealed Fe-rich microwires. For the wires after stress-annealing at variable temperatures we obtained a graded magnetic behavior with local hysteresis loops shapes and features (coercivity, remanent magnetization) changing along the sample length. In the samples subjected to local stress-annealing we created an artificial source of domain wall injection allowing the manipulation of domain wall dynamics. The observed stress-induced anisotropy could be related to the internal stress relaxation after annealing and the interplay of compressive “back-stresses” arisen after stress annealing and axial internal stresses.

Engineering of Magnetic Properties of Co- and Fe-Rich Microwires

We present our experimental results on optimization of the magnetic softness, domain wall (DW) dynamics, and giant magnetoimpedance (GMI) effect of Fe- and Co-rich microwires. It is found that the as-prepared Co-rich microwires possess much higher GMI effects and linear hysteresis loop. On the other hand, the magnetic softness and GMI effect of Fe-rich microwires can be improved by stress annealing. In addition, the DW velocity of the microwires can be considerably improved by annealing. The single DW propagation can also be observed in properly annealed Co-rich microwires. These observed dependencies can be attributed to the relaxation of internal stresses after annealing and the interplay of compressive stresses and axial internal stresses after stress annealing.

Tailoring of magnetoimpedance effect and magnetic softness of Fe-rich glass-coated microwires by stress- annealing

There is a pressing need for improving of the high-frequency magneto-impedance effect of cost-effective soft magnetic materials for use in high-performance sensing devices. The impact of the stress-annealing on magnetic properties and high frequency impedance of Fe-rich glass-coated microwires was studied. Hysteresis loops of Fe-rich microwires have been considerably affected by stress- annealing. In stress-annealed Fe- rich microwire we obtained drastic decreasing of coercivity and change of character of hysteresis loop from rectangular to linear. By controlling stress-annealing conditions (temperature and time) we achieved drastic increasing (by order of magnitude) of giant magnetoimpedance ratio. Coercivity, remanent magnetization, diagonal and of-diagonal magnetoimpedance effect of Fe-rich microwires can be tuned by stress-annealing conditions: annealing temperature and time. Observed experimental results are discussed considering relaxation of internal stresses, compressive “back-stresses” arising after stress annealing and topological short range ordering.

Optimization of high frequency magnetoimpedance effect of Fe-rich microwires by stress-annealing

We present comparative studies of magnetic properties and giant magnetoimpedance (GMI) effect of Fe and Co-rich microwires. As-prepared Co-rich microwires present much higher GMI ratio. The impact of the stress-annealing on magnetic softness and high frequency magnetoimpedance effect of Fe-rich microwires has been studied. The large improvement of the magnetoimpedance response in a wide frequency range by the stress-annealing is observed. We have achieved GMI ratio increase by an order of magnitude after stress-annealing of Fe-rich microwire. Observed stress-induced anisotropy and related changes of magnetic properties are discussed considering internal stresses relaxation and “back-stresses”.

Tailoring of magnetic softness and GMI effect in Fe-rich thin magnetic wires

We present comparative studies of magnetic properties and giant magnetoimpedance (GMI) effect of Fe and Co-rich microwires. As-prepared Co-rich microwires present much higher GMI ratio. The impact of the stress-annealing on magnetic softness and magnetoimpedance effect of Fe-rich microwires has been studied. The large improvement of the magnetoimpedance response by the stress-annealing is observed. We have achieved GMI ratio increase by an order of magnitude after stress-annealing of Fe-rich microwire. Observed stress-induced anisotropy and related changes of magnetic properties are discussed considering internal stresses relaxation and “back-stresses”.

Engineering of magnetic softness and giant magnetoimpedance effect in Fe-rich microwires by stress-annealing

Magnetic softness and giant magnetoimpedance (GMI) effect of Fe-rich microwires has been considerably improved by stress-annealing: we obtained maximum GMI ratio about one order higher than in as-prepared Fe-rich microwire and of the same order as in as-prepared Co-rich microwire. High enough bias current allows drastic increasing of GMI ratio of Fe-rich microwires up to 120% and off-diagonal GMI effect but also produces irreversible changes of GMI effect related to Joule heating of the samples. For interpretation of observed dependences we considered internal stresses relaxation after annealing interplay of compressive “back-stresses” arising after stress annealing and axial internal stresses.

Torsion Stress Induced Magnetic Switching in Amorphous Microwires

The mechanisms of magnetization reversal related to anisotropy change were analyzed using magneto-optical Kerr effect in Co- and Fe-rich microwires with different signs of magnetostriction. The reversible switching between inclined magnetic states and transformation of different inclined states was controlled by external torsion stress.

Engineering of giant magnetoimpedance effect of amorphous and nanocrystalline microwires

We present our studies of the factors affecting soft magnetic properties and giant magnetoimpedance effect in thin amorphous and nanocrystalline microwires. We showed that the magnetoelastic anisotropy is one of the most important parameters that determine magnetic softness and GMI effect of glass-coated microwires and annealing can be very effective for manipulation the magnetic properties of amorphous ferromagnetic glass-coated microwires. Considerable magnetic softening and increasing of the GMI effect is observed in Fe-rich nanocrystalline FINEMET-type glass-coated microwires after the nanocrystallization.

Effect of stress annealing on magnetic properties and GMI effect of Co- and Fe-rich microwires

Abstract We report on comparison of magnetic properties and GMI effect of as-prepared, annealed and stress-annealed Fe- and Co-rich microwires. Generally after annealing hysteresis loop of Co-rich microwires becomes rectangular. Stress annealed Co-rich microwires exhibit lower coercivity as-compared with conventionally annealed samples. Additionally we observed increasing of GMI ratio after stress annealing and its decreasing after conventional annealing. In the case of Fe-rich microwires the hysteresis loops of stress annealed samples present linear shape with low coercivity. Considerable improvement of GMI effect in Fe-rich microwires after stress annealing is observed. For interpretation of observed changes of hysteresis loops after stress annealing we considered internal stresses relaxation and different mechanisms of stress-induced anisotropy. Observed versatile properties of stress annealed glass-coated microwires with enhanced and tunable soft magnetic properties make them suitable for technological sensing applications.

Engineering of Giant Magnetoimpedance Effect of Amorphous and Nanocrystalline Microwires

We present an overview of the factors affecting soft magnetic properties and giant magnetoimpedance (GMI) effect of thin amorphous wires. Low coercivity and high GMI effect have been observed in as-prepared Co-rich microwires. We showed that the magnetoelastic anisotropy is one of the most important parameters that determines the magnetic softness and GMI effect of glass-coated microwires, and annealing can be very effective for manipulation of the magnetic properties of amorphous ferromagnetic glass-coated microwires. After annealing of Co-rich microwires, we can observe the transformation of inclined hysteresis loops to rectangle and coexistence of fast magnetization switching and GMI effect in the same sample. We demonstrated that the switching field value of microwires can be tailored by annealing in the range from 4 to 200 A/m. On the other hand in Fe-rich FeCuNbSiB microwires after appropriate annealing, we observed considerable magnetic softening and GMI effect enhancement.