K. Chichay

Tailoring of domain wall dynamics in amorphous microwires by annealing

We studied the effect of annealing on the magnetic properties and domain wall (DW) dynamics of magnetically bistable, Fe-based, glass-covered microwires with two different compositions, and different diameters. We observed the correlation of the domain wall dynamics with the distribution of the nucleation fields, measured in as-prepared samples, and after annealing for up to 150 min at temperatures of 250 and 300 °C. We found that both DW velocity and the range of the field limiting the single DW dynamics changed after annealing.

Investigation of the magnetostriction coefficient of amorphous ferromagnetic glass coated microwires

We measured the magnetostriction coefficient using small angle magnetization rotation method in amorphous ferromagnetic glass-coated Fe, Co, FeCo, and FeCoNi-based microwires. It was found that when the metallic nucleus of the microwire has a high magnetostriction—of the order (10–30) × 10−6 for FeCo-based microwires, the changing of diameters ratio, and hence, the magnitude and distribution of mechanical stresses have no significant effect on the value of the magnetostriction coefficient. In the case of nearly zero magnetostrictive FeCoNi-based microwires, increasing of the ρ−ratio leads to decreasing in the absolute value of the magnetostriction coefficient.

High-temperature magnetic behavior of soft/soft and soft/hard Fe and Co-based biphase microwires

The magnetic behavior of biphase magnetic microwires has been investigated in the high-temperature range from 295 to 1200 K. Bimagnetic microwires consist of a magnetically soft amorphous core (i.e., positive, FeSiB, and negative, CoFeSiB, magnetostriction alloy) and external polycrystalline shell with soft (FeNi, Permalloy) and medium-hard (CoNi) magnetic character. The magnetic phase transitions (ferro to paramagnetic) of individual phases are first detected through the temperature dependence of magnetization where structural changes in the amorphous alloy cores are also identified. Moreover, the values of coercive field of individual and bimagnetic phase systems are analyzed in view of these magnetic and structural transitions. The study is relevant for technological applications of bimagnetic microwires in the temperature regime above room temperature.

High Temperature Properties of CoFe/CoNi and Fe/CoNi Biphase Microwires

The objective of this work has been to analyze the high-temperature behavior of magnetically single-and biphase microwires because of its interest from fundamental and applications viewpoints. Two alloy compositions with amorphous structure covered by glass have been prepared as magnetically single phase microwires by quenching & drawing technique: CoFe-based with near zero saturation magnetostriction constant and Fe-based with positive saturation magnetostriction constant. The same wires were used as the core for magnetically biphase microwires. Second CoNi phase was deposited by electroplating. Magnitudes as saturation magnetization and hysteresis parameters are determined in the temperature range from room temperature up to 1200 K. We proceed to a comparative analysis of their magnetic behaviour at different temperatures as well as after cooling down to room temperature. Information on the Curie temperature of different phases and on the influence of heating process on the magnetic properties is thus derived.

Enhancement of Exchange Bias in NiFe/IrM, IrMn/NiFe and NiFe/IrMn/NiFe Structures with Different Thickness of Antiferromagnetic Layer

The Influence of the ferromagnetic (FM) and antiferromagnetic (AFM) layers position and of the thickness of antiferromagnetic (AFM) layer on magnetic properties of FM/AFM bilayer structures was studied. Angular dependences of the coercive force and exchange bias field were analyzed for NiFe/IrMn bilayer structures with different thickness of AFM layer. In some samples we observed the maximum values of the exchange bias field in the directions different from the magnetic easy axis.

Manipulation of Magnetic Properties and Domain Wall Dynamics in Amorphous Ferromagnetic Microwires by Annealing under Applied Stress

The effect of annealing under applied stress on magnetic properties of Co-based or CoFeNi-based glass-coated microwires was studied. It was found that CoFeNi-based microwires became bistable after annealing because of changing of magnetostriction constant sign, while Co-based microwires keep S-shape of hysteresis loop. The domain wall dynamics of microwires which became bistable was also investigated and it was shown that microwires with acquired bistability are more suitable for applications.

Temperature Dependent Magnetic and Structural Properties of Co2(Fe, Ti)Ga Thin Films

We report on the first study of magnetic and structural properties of Co2Fe1-xTixGa thin films prepared by a magnetron sputtering technique. The presence of well-defined (220) and (422) peaks corresponding to the principal reflection of the Heusler structure were revealed by XRD analysis. Results of magnetic properties measurements of the thin films showed that annealed samples have uniaxial in-plane anisotropy but magnetic properties of as-prepared samples exhibit anisotropy within the plane. The annealed thin films demonstrate complex magnetization process which can be attributed to the difference in the magnetic properties of two coexisting phases with B2 and L21 structural ordering.

Manipulation of Magnetic Properties and Domain Wall Dynamics of Amorphous Ferromagnetic Co68.7Fe4Ni1B13Si11Mo2.3 Microwire by Changing of Annealing Temperature

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