Juan Maria Blanco

Manipulation of domain wall dynamics in amorphous microwires through the magnetoelastic anisotropy

We studied the effect of magnetoelastic anisotropy on domain wall (DW) dynamics and remagnetization process of magnetically bistable Fe-Co-rich microwires with metallic nucleus diameters (from 1.4 to 22u2009μm). We manipulated the magnetoelastic anisotropy applying the tensile stresses and changing the magnetostriction constant and strength of the internal stresses. Microwires of the same composition of metallic nucleus but with different geometries exhibit different magnetic field dependence of DW velocity with different slopes. Application of stresses resulted in decrease of the DW velocity, v, and DW mobility, S. Quite fast DW propagation (v until 2,500u2009m/s at H about 30u2009A/m) has been observed in low magnetostrictive magnetically bistable Co56Fe8Ni10Si10B16 microwires. Consequently, we observed certain correlation between the magnetoelastic energy and DW dynamics in microwires: decreasing the magnetoelastic energy, Kme, DW velocity increases.

Coercivity of glass-coated Fe73.4-xCu1Nb3.1Si13.4+xB9.1 (0≤x≤1.6) microwires

Abstract The effects of the geometry, thermal treatment and the amplitude of applied magnetic field on the coercivity behaviour of glass covered Fe73.4-xCu1Nb3.1Si13.4+xB9.1 (x = 0; 1.1 and 1.6) have been investigated. Variations of the coercivity, Hc, with the geometry (d/D ratio, d –diameter of the metallic nucleus, D-total diameter, d/D ranging from 0.1 to 0.9) are attributed mainly to the internal stress acting on the metallic nucleus owing to the glass coating. Annealing temperature (300–700 °C) dependencies of Hc exhibit some peculiar differences with respect to that of the classical FINEMET ribbon, especially in the temperature range of 400–500 °C (very beginning of the nucleation of the nanocrystallization process) and at 650–700 °C (magnetic hardening owing to the iron borides segregation) depending in both cases on ratio d/D. With decreasing of d/D ratio the transition soft-hard magnetic character takes place in a narrower annealing temperature range with a rectangular hysteresis loop of Hc≈2400 A/m. The evolution of Hc with the applied magnetic field amplitude, Ho (

Evaluation of the saturation magnetostriction in nearly zero magnetostrictive glass-coated amorphous microwires

Measurements of the saturation magnetostriction λs of glass-coated covered (Co1−xMnx)75Si10B15 (x=0.09, 0.10 and 0.105) and Co56.5Fe6.5Ni10B16Si11 amorphous microwires carried out by means of the stress dependence of initial magnetic susceptibility method are reported. The conditions of applicability of this method to the microwires have been analyzed, taking into account the domain structure expected for very low negative magnetostriction of the metallic nucleus. The experimental data of λs obtained in those amorphous microwires are in agreement with those reported in amorphous ribbons with similar compositions.

Effects of tensile stress on the domain wall dynamics of Co-based amorphous ferromagnetic wires

Abstract Complex permeability measurements were performed on Co 72.5 B 15 Si 12.5 amorphous wires, as a function of tensile stress, at room temperature and in the frequency range 5 Hz – 13 MHz. Rotational and initial permeabilities showed a decrease as tensile stress increased. The domain wall relaxation frequency exhibited a linear behavior as stress increased. These results are interpreted in terms of the magnetoelastic contribution to anisotropy.

Tuning of Magnetic Properties and GMI Effect of Co-Based Amorphous Microwires by Annealing

We studied the effect of annealing on the giant magnetoimpedance (GMI) effect, magnetic domain wall dynamics, and magnetic properties of amorphous iron (Fe) and cobalt (Co)-based microwires prepared by the Taylor–Ulitovsky technique. We observed that the properties can be tailored by controlling the magnetoelastic anisotropy of CoFeBSiC microwires during wire formation and also controlling the magnetic anisotropy by further heat treatment. A high GMI effect has been observed in the as-prepared Co-based microwires. High domain wall velocity and rectangular hysteresis loops have been observed in additionally heat-treated microwires. We observed increasing of the wall velocity under stress in some annealed samples. We demonstrated that, for certain annealing conditions, we can observe coexistence of the GMI effect and magnetic domain wall propagation in the same sample.

Domain wall relaxation in Co-rich amorphous wires

Abstract The complex permeability in low-magnetostriction, as-cast CoFeBSi amorphous wires has been measured in the frequency range 5 Hz-13 MHz, and the applied field range 0.5–5.7 A/m. Cole-Cole plots showed characteristics associated with domain wall relaxation processes; wall relaxation frequencies exhibited an inverse behavior compared with the permeability. These results are interpreted in terms of a complex, multidomain structure in the core of the wire.

Effects of nanocrystallization on the magnetostriction of Co-based amorphous alloys

The influence of thermal treatments on the magnetostriction constant of Vitrovac/sup R/ 6025 amorphous alloys is reported. Annealing conditions (673 and 523 K at several annealing times) were chosen to result in nanocrystallization. The presence of nanocrystals led to a significant magnetic softening. No changes were observed on the saturation magnetization value at room temperature on the treated samples, as compared with the as-quenched sample. The magnetostriction constant, /spl lambda//sub s/, shifts from --0.14/spl times/10/sup -6/ for the as-quenched sample to positive values for the treated alloys. Samples annealed at 673 K exhibited two components of /spl lambda//sub s/ which depended on the tensile stress, /spl sigma/; one for low stress, and the other for high stress values, with the change at /spl sigma/=400 MPa. This behavior is interpreted in terms of a two-phase model, where one phase is the Fe-enriched residual amorphous fraction, and the other one is formed by Co-rich nanocrystals. For annealing at 723 K, a well-known relationship, /spl lambda//sub s/(/spl sigma/)=/spl lambda//sub s/(0)-A/spl sigma/, was observed, with no resolution of components. This difference is interpreted on the basis of the nanocrystals size: for 673 K, the nanocrystals are smaller than the exchange length, while they are larger for 723 K. >

Simultaneous Detection of Giant Magnetoimpedance and Fast Domain Wall Propagation in Co-Based Glass-Coated Microwires

The magnetic properties of as-prepared and annealed amorphous Co50.69Fe8.13Ni17.55B13.29Si10.34 and glass-coated microwires produced by the Taylor-Ulitovsky technique are investigated systematically. Magnetic-field frequency dependences of magnetoimpedance (MI), domain-wall (DW) velocity, and hysteresis loops were measured. At certain annealing conditions, high MI and fast DW propagation simultaneously coexist. The results suggest criteria for the selection of materials for high-performance magnetic sensors.

Magnetoelastic Effects and Distribution of Defects in Micrometric Amorphous Wires

The influence of defects and the magnetoelastic anisotropy term on the domain wall dynamics of glass-coated amorphous microwires is investigated. Using modified Sixtus-Tonks set-up, we have determined the position of the domain nucleation and measured the magnetic field dependence of the domain wall velocity. We found that both internal and applied stresses significantly affect the domain wall dynamics especially for wires with reduced magnetostriction. Particularly, we conclude that the non-linear relationship between the do- main wall velocity and magnetic field is correlated with the existence of defects which act as nucleation centers of additional domains.

Effective Anisotropy And Magnetostriccion Of The Amorphous And Nanocrystalline Fe/sub 83/Zr/sub 7/B/sub 8/Cu/sub 2/ Alloy

The effective magnetic anisotropy and saturation magnetostriction of both amorphous and nanocrystalline (samples with different microstructures) Fe/sub 83/Zr/sub 7/B/sub 8/Cu/sub 2/ alloy have been investigated. The effective anisotropy results were obtained through the measurement of the bias field dependence of the transverse susceptibility in samples annealed from 480 to 600/spl deg/C. In the above mentioned range, the annealing temperature dependence of the saturation magnetostriction is related to the presence of a nanocrystalline structure leading to a remarkable magnetic softening. From our results it was possible to discern the occurrence of intergranular coupling and to evaluate the typical dimensions of the coupled units.