M. Churyukanova

Magnetostriction of Co–Fe-Based Amorphous Soft Magnetic Microwires

We studied the correlation between magnetic softness and magnetostriction coefficient for as-prepared and annealed Co–Fe-rich microwires. We found that the hysteresis loops and magnetostriction coefficients of Co and Fe-rich microwires depend not only on the chemical composition of the metal but also on internal stress. Consequently, both hysteresis loop and magnetostriction coefficient can be adjusted by annealing. We varied the time and temperature of annealing and observed changes of the character of the hysteresis loops. These changes correlated with evolution of the magnetostriction coefficient. Drastic changes of the hysteresis loop for Co-rich microwires were attributed to changes of the sign and value of the magnetostriction coefficient.

Influence of the defects on magnetic properties of glass-coated microwires

We observed different kind of defects, such as gas bubbles, glass coating thickness inhomogeneities, indications of the chemical interaction between the glass shell and the metallic nucleus. We showed that the existence of such bubbles might be the origin of the spontaneous fluctuations of the local nucleation field.

Studies of High-Frequency Giant Magnetoimpedance Effect in Co-Rich Amorphous Microwires

We studied giant magnetoimpedance (GMI) effect and magnetic properties of various Co-rich amorphous microwires. We measured the values of magnetic field dependence of the GMI ratio up to gigahertz frequency range, and observed quite high GMI ratio in as-prepared Co-rich microwires even at gigahertz frequencies. We observed the different values of the magnetic anisotropy field obtained from the hysteresis loops and the impedance curves. Observed dependence can be explained considering different magnetic anisotropy in the surface layers and in the inner part of metallic nucleus and skin depth effect. Features of high-frequency GMI effect have been analyzed using ferromagnetic resonance-like approximation.

Formation of Intermetallic Ni-Al Coatings by Mechanical Alloying with Different Intensities

Intermetallic Ni-Al coatings on the Ni substrate were prepared by the mechanical alloying (MA) method in mechanical activators of vibratory and planetary type. It was found that coatings that were fabricated in a high-energy (planetary) activator in comparison with those fabricated in a low-energy (vibratory) activator are more homogeneous, have higher density, and experience better adhesion to the substrate. It was shown that different intermetallic phases (NiAl, NiAl3, and Ni2Al3) can form directly during the MA treatment in the planetary activator.

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.

Studies of the Defects Influence on Magnetic Properties of Glass-Coated Microwires

Using local nucleation field technique, electronic microscopy, and optical microscopy, we studied different kind of defects in glass-coated microwires. We observed variation of Fe and Si content along the microwires and oxygen presence in defective regions on the metallic nucleus surface and indications of chemical interaction between the glass-coating and metallic nucleus.

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.

CoFe-microwires with stress-dependent magnetostriction as embedded sensing elements

Testing internal stress/strain condition of polymer composite materials is of high importance in structural health monitoring. We are presenting here a new method of monitoring internal stresses. The method can be referred to as embedded sensing technique, where the sensing element is a glass-coated ferromagnetic microwire with a specific magnetic anisotropy and stress-dependent magnetostriction. When the microwire is remagnetized the sharp voltage is induced which is characterized by high frequency harmonics. The amplitude of these harmonics sensitively depends on various stresses. The microwire of composition Co71Fe5B11Si10Cr3 with the metallic core diameter of 22.8 μm show abrupt transformation of the magnetization process under applied tensile stress owing to the stress-dependent magnetostriction.

Magnetic Properties and Defects of Fe-Ni-Based Magnetic Microwires

We studied the magnetic properties and domain wall (DW) dynamics of Fe_47.4Ni_26.6Si₁₁B₁₃C₂ and Fe_77.5Si_7.5B₁₅ microwires. Both samples present a rectangular hysteresis loop and fast magnetization switching. The linear region of dependence of the DW velocity on the magnetic field in Fe_47.4Ni_26.6Si₁₁B₁₃C₂ sample is considerably shorter. Consequently, we studied the structure of Fe_47.4Ni_26.6Si₁₁B₁₃C₂ sample using X-ray diffraction and atom probe tomography. The results obtained using the atom probe tomography supports the formation of B-enriched precipitates in the interfacial layer and in the metallic nucleus after annealing.

First-order martensitic transformation in Heusler-type glass-coated microwires

Properly annealed Ni-Mn-Ga glass-covered microwires exhibit a hysteretic anomaly on the temperature dependence of magnetization attributed to the first order martensitic transformation. The temperatures of the structural and magnetic transitions are drastically affected by annealing conditions. Annealed glass-coated Ni-Mn-Ga microwires show a Curie temperature shift close to room temperature. The temperature and magnetic field dependences of magnetization are discussed in terms of atomic disorder, the release of internal stresses, and recrystallization after annealing.Properly annealed Ni-Mn-Ga glass-covered microwires exhibit a hysteretic anomaly on the temperature dependence of magnetization attributed to the first order martensitic transformation. The temperatures of the structural and magnetic transitions are drastically affected by annealing conditions. Annealed glass-coated Ni-Mn-Ga microwires show a Curie temperature shift close to room temperature. The temperature and magnetic field dependences of magnetization are discussed in terms of atomic disorder, the release of internal stresses, and recrystallization after annealing.