V. Rodionova

Domain wall propagation in micrometric wires: Limits of single domain wall regime

We measured magnetic domain propagation and local domain wall(DW) nucleation in Fe-Co-rich amorphous microwires with metallic nucleus diameters from 2.8 to 18 μm. We found that manipulation of magnetoelastic energy through application of applied stresses, changing of magnetostriction constant, and variation of internal stresses through changing the microwires geometry affects DW velocity. We observed uniform or uniformly accelerated DW propagation along the microwire. The abrupt increasing of DW velocity on v(H) dependencies correlates with the location of the nucleation place of the new domain wall.

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.

Manipulation of domain wall dynamics in amorphous microwires through domain wall collision

Experimental results of the magnetic field driven domain walls dynamics in magnetically bistable Fe-rich microwires are reported. We have observed that under certain conditions a controllable domain wall (DW) collision can be realized in different parts of the wire, and that it is possible to manipulate the DW dynamics in a field-driven regime. The DW collisions obtained in this way can be used to release pinned domain walls. We have also found a correlation between the local nucleation field distribution and field dependence of DW velocity: the magnetic field value corresponding to the minimum nucleation field determines a threshold between single and multiple domain wall propagation regimes.

Temperature-Dependent Magnetic Properties of Magnetically Biphase Microwires

The magnetic behaviour of soft/hard biphase magnetic microwires has been studied as a function of temperature in the range 25°C to 900°C. The microwires consist of an ultrasoft CoFe-based vanishing magnetostriction amorphous core covered by insulating Pyrex coating prepared by quenching and drawing, plus an electroplated CoNi magnetically harder external shell. The magnetization process has been analyzed through the study of the hysteresis loops and their parameters like saturation magnetization and coercivity of the different phases, measured in a vibrating sample magnetometer. The magnetically biphase character has been first confirmed by room-temperature measurements for wires with different thickness. The observed dependence of magnetization and coercivity on temperature is correlated with the overcoming of the Curie temperature and crystallization of the amorphous soft core.

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.

Internal stress induced texture in Ni-Mn-Ga based glass-covered microwires

We have studied magnetic and structural properties of the composite microwires consisted of the metallic core and the outer glass shell. Nominal chemical composition of the core was Ni49.5Mn25.4Ga25.1, its diameter was 13.2 μm, and the total diameter of the glass-covered microwires was 26.4 μm. We have found out that at room temperature the core of the as-cast microwires was composed by two phases with tetragonal I4/mmm and cubic Fm3m crystal structures, but annealing rendered it single phase. Measurements of the magnetic properties have demonstrated substantial growth of the magnetic anisotropy with cooling, which we have attributed to the phase transition from the room-temperature austenitic to the low-temperature martensitic state. Magnetic easy axis was found to be perpendicular to the axis of the microwires at low temperatures. We believe that it is a result of the crystallographic texture induced in the martensite by high internal stress characteristic of the glass-covered magnetic microwires. Thoug...

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.

Magnetic Properties of Heusler-Type Microwires and Thin Films

In this paper, we studied magnetic properties of Heusler-type glass-covered microwires and thin films. The results have shown that we succeeded to prepare Ni-Mn-In thin films and Ni-Mn-Ga and Ni-Mn-In microwires that have martensitic and austenitic phases at room temperature.

Highly Textured FeCo Thin Films Deposited by Low Temperature Pulsed Laser Deposition

The effect of the deposition temperature (Tdep) on the crystallographic orientation of pulsed laser-deposited FeCo/MgO(100) thin film was determined by means of X-ray reflectivity and high resolution trasmission electron microscopy analysis and was correlated with the magnetic anisotropy properties measured by angle dependent hysteresis loops. Highly textured films with a bcc structure and very smooth surface were obtained even at room temperature, the film being [100] and [110] oriented, at Tdep=25 °C and 150 °C, respectively. The cubic symmetry is reflected in the angular dependence of remanent magnetization, showing a 4-fold character, whose in-plane distribution is consistent with the different crystallographic orientations of the films. The high structural quality, even at room temperature, is reflected in a high value of the saturation magnetization and low coercivity, matching the requirements for technological applications.

Ni-Mn-In Heusler Alloy Thin Films Grown by Pulsed Laser Deposition

We report on the results of the magnetic and structure properties investigation of Heusler alloy films. Ni-Mn-In thin films were formed by pulsed laser deposition. Stoichiometry was varied and controlled by co-deposition technique. The different deposition conditions and influence of the annealing temperature on the film composition were investigated using Auger electron spectroscopy and Rutherford backscattering spectrometry. The optimal annealing temperature was found to be 620 K. The set of the films deposited on the oxidized Si (100) substrate at room temperature and annealed at 620 K was investigated using X-ray diffractometry at room temperature and Vibrating sample magnetometery at low temperatures. The crystal structure was found to be a mixture of austenitic and martensitic phases at room temperature. Decreasing of Curie temperature from 270 K to 250 K with the decreasing of In concentration from 20 at % to 15 at % was observed.