FeCoMoB Microwires Research Articles

Effect of Annealing on Domain Wall Mass in Amorphous FeCoMoB Microwires

The effect of annealing on the domain wall mass in amorphous FeCoMoB microwires has been studied. Annealing at 300 °C for 1 h leads to the relaxation of strong stresses from production process and to the homogenization of its amorphous structure. As a result of such annealing, the domain wall mass decreases from $1.26\times 10^{-15}$ kg in the as-cast state to $0.72\times 10^{-15}$ kg in the annealed state, while the thickness of the domain wall exhibits opposite tendency and increases from 493 nm in the as-cast state to 808 nm in the annealed sample.

Effect of Current Annealing on Domain Structure in Amorphous and Nanocrystalline FeCoMoB Microwires

Effect of Current Annealing on Domain Structure in Amorphous and Nanocrystalline FeCoMoB Microwires

Effect of Current Annealing on Domain Wall Dynamics in Bistable FeCoMoB Microwires

We have studied effect of current annealing on domain wall dynamics of FeCoMoB microwires. It was showed that 10 minutes of current annealing corresponds to 1 hour of classical annealing in furnace. Moreover, electrical current flowing through microwire produces Oersted magnetic field and therefore circular magnetic anisotropy is induced during annealing. As a result, induced circular magnetic anisotropy prefers vortex domain wall with velocities up to 3 km/s that can be observed in the current annealed nanocrystalline FeCoMoB microwires with much higher temperature stability.

Enhancing the velocity of the single domain wall by current annealing in nanocrystalline FeCoMoB microwires

The effect of current annealing on the velocity of the single domain wall, sDW, and its dynamic stability is investigated in the 80–400 K temperature range for FeCoMoB nanocrystalline microwires. In addition to the heating effect of thermal treatments in a conventional field-free furnace, current annealing induces circumferential magnetic anisotropy, which significantly modifies the sDW dynamics characteristics. Such an anisotropy leads to an increased high domain wall velocity with a maximum measured value of about 8 km s−1. An unexpected increase in the domain wall velocity and mobility at 175 K is ascribed to the compensation of the anisotropy distribution. Finally, the domain wall dynamics exhibit very stable behaviour in a wide range of temperatures (200–400 K).

Domain wall dynamics in nanocrystalline microwires

AbstractThe domain wall velocity in amorphous microwires approaches very high values up to 20 km/s but dynamics is extremely sensitive to time and temperature. On the other hand, high stability in crystalline materials is paid by very low velocity of the domain wall. One possible solution is using of nanocrystalline material, which are produced by controlled annealing from amorphous precursors. Domain wall velocity reaches up to 1 km/s in nanocrystalline microwires based on FINEMET composition. In different group of nanocrystalline microwires based on HITPERM composition was observed temperature stable and fast domain wall up to 3 km/s. In the present contribution, we present new class of nanocrystalline microwires based on FeNiMoB composition, where domain wall velocity up to 12 km/s was observed. In generally, domain wall velocity increases by annealing in FeNiMoB microwires in contrary to FeCoMoB microwires. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Stable and fast domain wall dynamics in nanocrystalline magnetic microwire

The domain wall dynamics in the nanocrystalline FeCoMoB microwire has been investigated in the temperature range from 80 to 450K. A fast domain wall motion is observed in the whole temperature range with velocity up to 1500m/s. The domain wall mobility at low fields is extremely stable, and only slight variations in the whole temperature range are observed reflecting the temperature dependence of the saturation magnetization. At higher fields, the velocity in vortex regime varies with temperature but it approaches very high values up to 3000m/s.

Domain Wall Dynamics in Amorphous and Nanocrystalline FeCoMoB Microwires

We have studied the domain wall dynamics in amorphous and nanocrystalline FeCoMoB microwires. The domain wall propagation velocity has been found very fast (up to 5000 m/s) for the as-cast sample. Annealing at 575 K/1 h leads to the stress relief and sample homogenization and the domain wall velocity even increases to 5300 m/s. However, the domain wall dynamics is highly sensible to the temperature of a measurement. Annealing at 775 K/1 h leads to the appearance of the nanocrystalline structure with much higher temperature stability. The maximum domain wall velocity decreases (2800 m/s), however the domain wall dynamics is much stable with the temperature.

Ferromagnetic resonance study of FeCoMoB microwires during devitrification process

Magnetic properties of FeCoMoB glass-coated microwires with high positive magnetostriction have been investigated during the process of devitrification in the temperature range: 0-600 °C by ferromagnetic resonance (FMR) studies. The FeCoMoB microwire shows natural ferromagnetic resonance that reflects a complex anisotropy distribution. FMR spectrum for as cast sample shows up to four resonance maxima when ranging frequency from 10 MHz up to 11.3 GHz. After annealing, the anisotropy distribution becomes more regular and the number of FMR peaks decreases. The anisotropy and stress amplitude has been estimated from the FMR spectra, showing a strong decrease with annealing temperature and being low and constant for the nanocrystalline state. In addition, Gilbert damping decreases with annealing temperature, too. The low Gilbert damping (∼0.01) for the nanocrystalline state makes the nanocrystalline FeCoMoB microwire an ideal material for applications in which fast magnetization processes are required.

Fast domain wall dynamics in amorphous and nanocrystalline magnetic microwires

We have studied the effect of thermal treatment on the domain wall dynamics of FeSiB and FeCoMoB microwires. It was shown that annealing in transversal magnetic field increases the domain wall mobility as well as the domain wall velocity. Annealing under the tensile stress hinders the appearance of the monodomain structure but application of tensile stress leads to the magnetic bistability having the domain wall mobility twice higher that in as-cast state. Further increase of the tensile stress reduces the domain wall mobility but the domain wall velocity increases as a result of the decrease of critical propagation field. Annealing of the FeCoMoB microwire by Joule heating leads to introduction of the circular anisotropy that favors the vortex domain wall. Such treatment increases the domain wall mobility as well as the maximum domain wall velocity.

Study of domain structure and magnetization reversal after thermal treatments in Fe40Co38Mo4B18 microwires

We have studied the effect of thermal treatment on the magnetic domain structure and magnetic reversal process of amorphous and nanocrystalline Fe40Co38Mo4B18 microwires. The domain structure and the magnetization reversal of amorphous FeCoMoB microwires reflect the complex stress distribution introduced by the glass coating. Hence, the thickness of radial domain structure decreases with temperature and the temperature dependence of the switching field presents a discontinuous behavior. After nanocrystallization, the domain structure of FeCoMoB microwire is almost constant within the temperature range 10–400K and the switching field decreases almost linearly with temperature mostly because of the decrease of saturation magnetization.

In situ structural investigation of amorphous and nanocrystalline Fe 40Co 38Mo 4B 18 microwires

Thermal evolution of the structure of glass-coated nanocrystalline FeCoMoB microwire during its devitrification has been studied. It is shown that annealing at the temperature above 411 °C leads to the formation of crystalline α-FeCo grains with diameter ∼12 nm. Annealing at higher temperature increases the crystalline weight fraction up to 40% at 565 °C. However, crystalline grains size increases very weakly to ∼13 nm. The thermal expansion coefficient of nanocrystalline microwire decreases by one half comparing to that of the amorphous precursor.

Temperature Dependence of Magnetization Process in Bistable Amorphous and Nanocrystalline FeCoMoB Microwires

We have studied the effect of thermal treatment on the magnetic properties of amorphous and nanocrystalline Fe40Co38Mo4B18 microwires. The magnetization process was measured within the temperature interval from 80 to 425 K. Microwires shows complex temperature dependence of the switching field in amorphous state due to the presence of complex stress distribution induced during production. After nanocrystallization, the switching field depends linearly on the measuring temperature that makes such microwires ideal for sensing applications.

Study of the Switching Field in Amorphous and Nanocrystalline FeCoMoB Microwire

We have studied the frequency dependence of switching field in a wide range of frequencies in amorphous and nanocrystalline microwires with nominal composition Fe40Co38Mo4B18. Samples were heat treated for 1 h at different temperatures in a wide temperature range 20-600°C. Three regions in the frequency dependence of the switching field were identified. Drop of switching field at low frequencies up to 50 Hz is explained in term of structural relaxation. Above 50 Hz the magnetoelastic contribution of the switching field is dominant. The magnetoelastic contribution of the switching field can be fitted by the power law (H sw ? ~ f1/n), giving exponent n equal 2 for frequency below 1000 Hz for all studied samples. Above 1000 Hz, the switching field reflects the structure of microwire being highly frequency dependent in as-cast sample and sample annealed at 450°C (where the microwire is quite inhomogeneous) while its frequency dependence is very weak for other annealing temperatures. Moreover, power exponent n gives non-physical values (~ 100) in this range.

Bistable FeCoMoB microwires with nanocrystalline microstructure and increased Curie temperature

Novel nanocrystalline glass-coated Fe40Co38Mo4B18 microwires are introduced. They combine the advantages of nanocrystalline alloys exhibiting simultaneously increased Curie temperature and magnetic bistability, which is required for modern sensoric and spintronic devices. Positive magnetostriction of the crystalline FeCo grains results in a magnetic bistability, whereas good soft magnetic properties remain stabilized. As a result of the mechanical stress induced by the glass coating, the optimum temperature range for thermal treatment is enhanced up to 600 °C.