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1
Content available remote

Asymmetric Magneto-Impedance in CoFeSiB Amorphous Microwire

100%
Kravčák J., Varga R.
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issue 5
762-763
EN
The symmetric dependences of magneto-impedance on the applied longitudinal dc magnetic field were measured in an amorphous CoFeSiB microwire. Additional application of a circumferential dc bias magnetic field was used to achieve the asymmetric magneto-impedance in the microwire. The obtained results are theoretically interpreted taking into account the cylindrical core-shell magnetic structure and the helical anisotropy induced during the microwire preparation. The observed very steep linear magneto-impedance dependences crossing H = 0 are promising for technical applications of the CoFeSiB microwire as a sensor of low magnetic fields.
2
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Angular Dependence of Magnetization Reversal in Microwire Studied by MOKE

100%
Váhovský O., Varga R.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
648-650
EN
In this work we present magneto-optical Kerr effect study of magnetization processes in amorphous glass - coated microwire of composition Fe_{77.5}Si_{7.5}B_{15}. Unique results obtained from microwire were compared to results of similar measurements on polycrystalline ribbon Co_2FeSi. In both cases reversal of longitudinal and transversal component of surface magnetization was studied. There was just a small variation in total change of magnetization caused by change in the direction of magnetic field in case of square hysteresis loops measured on microwire. However, switching field was angularly dependent and the change was considerably high and well predictable. The last two facts make such microwires outstanding candidates for sensors of magnetic field direction or spatial orientation.
3
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Influence of Thermal Treatment on Domain Wall Dynamics in Glass-Coated Microwires

81%
Richter K., Varga R., Zhukov A.
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issue 5
738-739
EN
We have studied the effect of thermal treatment on amorphous glass-coated Fe_{40}Si_{7.5}B_{15} microwires. This microwire is characterized by transverse domain wall regime only, with maximum domain wall velocity of about 1500 m/s. Annealing at 200°C slightly increases its transverse domain wall velocity, probably due to the reduction of mechanical stresses during the thermal annealing. Annealing at 300°C leads to drastical increase of domain wall mobility and domain wall velocity of the transverse domain wall up to 2500 m/s. Moreover, vortex regime appears in this case. Thanks to it, maximum domain wall velocity of around 5000 m/s was observed.
4
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Temperature Dependence of the Switching Field in Nanocrystalline FeNiMoB Microwires

81%
Klein P., Varga R., Vazquez M.
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vol. 126
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issue 1
64-65
EN
We have studied temperature dependencies of the switching field in as-cast and nanocrystalline glass-coated Fe_{40}Ni_{38}Mo_{4}B_{18} microwires. The switching field shows complex temperature dependence in the as-cast state reflecting the complex stress distribution induced during annealing. The temperature dependence of the switching field depends strongly on the stage of nanocrystallization being negative for low temperatures of annealing and positive for annealing at 700 K.
5
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Complex Permeability After-Effect and Analysis of Power Losses in Ferromagnetic Co-Based Amorphous Alloy

81%
Kravčák J., Varga R., Vojtaník P.
Acta Physica Polonica A
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2008
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vol. 113
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issue 1
43-46
EN
Complex permeability (μ=μ_1-iμ_2) after-effect of near-zero magnetostrictive CoFeCrSiB amorphous alloy was investigated in magnetic field H (t)= H_0exp ( i 2π f t) after demagnetization. For frequencies f from 200 Hz to 2000 Hz and for the small amplitude H_0 < H_{cr} we observed practically constant both realμ_1 and imaginary part μ_2 of permeability. A measured small decrease in the real part μ_1 and increase in the imaginary part μ_2 with frequency f were theoretically calculated for a quadratic form of a domain wall potential E_S (x)=1/2α x^2. The calculated loss factortan δ =μ_2μ_1, which is small at amplitude H_0 < H_{cr}, corresponds to power losses due to eddy currents induced around reversibly moving domain walls.
6
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Negative Mobility of Single Domain Wall in Magnetic Microwires

81%
Varga R., Richter K., Zhukov A.
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issue 5
747-748
EN
Here, we present the domain wall dynamics in thin magnetic wires that exhibit even negative mobility regime. Such a regime is well below the Walker limit and is a result of structural relaxation. It disappears at high frequencies and it can be enhanced by application of mechanical stress. Moreover, the domain wall velocity was found to be almost field-independent at certain measuring conditions. Anyway, the domain wall velocity remains quite high (> 450 m/s) in this regime.
7
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Perminvar Effect in Amorphous Hitperm Alloy

81%
Varga M., Varga R., Vojtanik P., Komova E.
Acta Physica Polonica A
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2008
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vol. 113
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issue 1
119-122
EN
Influence of the directional ordering on magnetization processes in the amorphous Fe_{44.5}Co_{44.5}Zr_7B_4 alloy was investigated in the temperature region of 27 to 300°C for stabilization times of up to 1000 min by means of the Perminvar effect. The time-temperature dependent Perminvar effect was found to be very sensitive on the stage of the domain structure stabilization. The Perminvar critical fields H_{CR} were shifted to higher values with increasing stabilization temperatures and times. At lower temperatures, the susceptibility increases over wide range of the measuring fields. Stabilization at higher temperatures causes that the susceptibility abruptly increases in the narrow field range. The record critical field H_{CR} =246 Am^{-1} was obtained.
8
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Imaging the Surface Domain Structure of Amorphous Glass-Coated Microwires by Bitter Colloid

81%
Richter K., Varga R., Thiaville A.
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vol. 126
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issue 1
72-73
EN
The fast domain wall dynamics of amorphous glass-coated microwires can be changed drastically by properly selected annealing temperature. Here, the effect of thermal annealing on the surface domain structure of microwires is examined. Imaging the surface domain structure by Bitter colloid revealed the periodic pattern in each studied sample. Thermal annealing of microwires results in the five times increase of the domain wall velocity, as compared to the as-cast state. Influence of the surface domain structure on the fast domain wall propagation in microwires is discussed.
9
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The Study of Magnetization Process in Amorphous FeNiSiB Microwires

81%
Gamcova J., Varga R., Hernando B., Zhukov A.
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issue 5
807-808
EN
We have studied the magnetization process in amorphous Fe_{49.6}Ni_{27.9}Si_{7.5}B_{15} microwire. It was found that the hysteresis mechanism consists of two contributions: magnetoelastic and structural relaxation. It was shown that at low frequencies, the magnetization process is controlled mainly by the structural relaxation. At higher frequencies (above 50 Hz), the relaxation effect disappears and switching field is determined mainly by the magnetoelastic contribution. Moreover, the effect of thermal treatment at temperature 300°C has been studied. As-cast microwire is almost unsensible to the applied tensile stress since the applied stresses are lower than that induced during production. After annealing, the stresses relax and stress sensibility of microwires increases.
10
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Magnetic Properties of Glass-Coated FeWB Microwires

81%
Klein P., Varga R., El Kammouni R., Vazquez M.
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vol. 126
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issue 1
70-71
EN
We have studied magnetization process in amorphous bistable Fe_{80}W_{3}B_{17 } microwires with reduced Curie temperature. High mechanical stresses from glass-coating, induced during production process, result in high switching field. Reducing the length of microwire, the switching field decreases as a result of reduction of magnetoelastic anisotropy. Moreover, the decrease of magnetoelastic anisotropy results in a complex temperature dependence of the switching field. On the other hand, strong variations of the switching field with temperature can be employed in miniaturised temperature sensor.
11
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Temperature Dependence of Magnetization Process in Bistable Amorphous and Nanocrystalline FeCoMoB Microwires

81%
Klein P., Varga R., Vazquez M.
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issue 5
809-810
EN
We have studied the effect of thermal treatment on the magnetic properties of amorphous and nanocrystalline Fe_{40}Co_{38}Mo_4B_{18} 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.
12
Content available remote

Complex Magnetoimpedance in Joule-Heated Co_{71,1}Fe_{3,9}Si_{10}B_{15} Microwires

81%
Komova E., Kozar J., Klein P., Varga R.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
705-707
EN
Complex magnetoimpedance study is an alternating current technique that can be used to probe some properties of magnetic materials. We report on complex impedance measurements in low-negative magnetostrictive ferromagnetic CoFeSiB microwire. In these wires, the domain structure consists of two parts: an inner core, with domains oriented to the longitudinal direction of the wire, and an outer shell with circumferentially oriented domains. This magnetic structure is modified by AC current flowing through the microwire which produces an additional circumferential magnetic field H_Φpand significantly affects magnetic structure inside the wires. The additional circular magnetization process in wires was studied by impedance measurements as a function of the amplitude and the frequency of the AC current after gradual Joule heating. Changes in the magnetization processes are reflected in the real permeability values and loss factor values.
13
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Influence of Thermal Treatment on Frequency Dependence of the Switching Field in Amorphous and Nanocrystalline FeNiMoB Microwires

81%
Komova E., Varga R., Vazquez M.
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issue 5
768-769
EN
Amorphous and nanocrystalline ferromagnetic glass-coated microwires show excellent magnetic properties that make them very suitable to be employed as sensing elements in devices for technical applications. New Fe_{40}Ni_{38}Mo_4B_{18} alloy composition can be appropriate to prepare soft magnetic nanocrystalline microwires which exhibit magnetic bistability even in the nanocrystalline state. Stability of magnetic properties after different thermal treatments (T_{a} = 250-425°C) and after nanocrystallization was confirmed by the switching field H_{sw} measurements. The frequency dependence of the switching field was investigated. Two contributions to the domain wall switching mechanism were recognized: magnetoelastic one coming from the magnetoelastic interaction of the magnetic moments with the stresses and relaxation one coming from the structural relaxation of local defects at atomic scale. But, the relative role of both contributions has been shown to vary strongly in different stage of devitrification.
14
Content available remote

Single Domain Wall Propagation at Low Fields

81%
Kostyk J., Varga R., Vazquez M.
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vol. 126
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issue 1
30-31
EN
We have studied the domain wall propagation at low fields regime in thin glass-coated microwire of composition Fe_{77.5}Si_{7.5}B_{15}. It is shown, that power law describes domain wall dynamics at low fields. Such behaviour results from the interaction of the propagating domain wall with the defects present in the material. At high fields, the domain wall mobility becomes negative. This can be explained as a result of domain structure relaxation. The exponent q from power law, which determines the domain wall shape, has a value of 0.19 for both cases, without applied stress and with applied stress of 20 MPa. This means, that domain wall shape is flexible in both measurements.
15
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GMI Effect in Annealed Fe_{40}Ni_{38}Mo_{4}B_{18} Microwires

71%
Komova E., Šidik F., Klein P., Varga R., Vazquez M.
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vol. 126
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issue 1
74-75
EN
Amorphous glass-coated microwires are ideal material for miniaturized applications for sensing the temperature, stress and magnetic field. One of the key parameters for future applications is their time and thermal stability. It has been shown that stability can be improved by using nanocrystalline materials that combine good soft magnetic properties of amorphous matrix with high structural stability of crystalline grains. Such nanocrystalline materials are usually obtained by annealing of amorphous precursor. In the given contribution, the influence of dc current annealing on the domain structure and GMI effect in amorphous and nanocrystalline Fe_{40}Ni_{38}Mo_{4}B_{18} magnetic microwire has been studied. The annealing induces additional circular magnetic anisotropy, stress relief and structure homogenization. However, the increase of magnetostriction results in the decrease of GMI. Annealing at optimum crystallisation temperature results in an increase of the relative permeability due to the formation of the nanosized grains. Consequently, GMI amplitude is comparable to that of as-cast state.
16
Content available remote

Domain Wall Dynamics in Amorphous Microwires

71%
Richter K., Kostyk Y., Varga R., Zhukov A., Larin V.
Acta Physica Polonica A
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2008
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vol. 113
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issue 1
7-10
EN
Here we present the domain wall dynamics in FeNi-based microwires with positive magnetostriction. Two different ranges were found which differs by the measured domain wall mobility. At low fields, the domain wall dynamics exhibit small mobility, whereas at higher field the domain wall mobility increases. The difference in the two regimes of the domain wall dynamics is treated in terms of the different domain wall structure. At low fields, the transversal domain wall is expected, with low domain wall mobility. At high field, the vortex-type domain wall with high domain wall mobility is created.
17
Content available remote

Influence of Mn Doping on Magnetic and Structural Properties of Co₂FeSi Heusler Alloy

62%
Galdun L., Ryba T., Kováč J., Prida V., Hernando B., Vargová Z., Varga R.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
866-868
EN
We have studied the effect of Mn doping on structural and magnetic properties of Co₂FeSi Heusler alloy. Co₂FeSi, Co₂Mn_{0.25}Fe_{0.75}Si and Co₂Mn_{0.5}Fe_{0.5}Si alloys were prepared by melt spinning technique which offers fast and simple production of large amount of materials in a single production step. The rapid quenching method provides an opportunity to prepare Heusler alloys with highly ordered L2₁ structure confirmed by X-ray analysis in all the samples. Magnetic measurements revealed high Curie temperatures (>1000 K) and well defined easy magnetization plane parallel with the ribbon plane. Those attributes predispose given samples for applications in spintronics.
18
Content available remote

Structure of Melt-Spun Co₂MnAl Heusler Alloy

62%
Piovarči S., Diko P., Kavečanský V., Ryba T., Vargová Z., Varga R.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
881-883
EN
The growth-related microstructure and texture of the Co₂MnAl-type Heusler alloy in the form of a melt-spun ribbon was studied by electron microscopy, electron backscattered diffraction and X-ray diffraction. It is shown that melt spinning produces a single-phase disordered Heusler alloy. The fine grain structure at the wheel side of the ribbon exhibits no texture, while dominant columnar grain structure formed on the free surface side exhibits the ⟨111⟩ fibre texture with a declination by about 10 degrees in the spinning direction. The dendritic growth of columnar crystals causes inhomogeneity of the chemical composition on a micrometre scale with a higher Co and Al concentration in the centre of dendritic arms and a higher concentration of Mn at the dendrite arm boundaries.
19
Content available remote

Stress Dependence of the Switching Field in Glass Coated Microwires

62%
Komová E., Varga M., Varga R., Vojtaník P., Torrejon J., Provencio M., Vázquez M.
Acta Physica Polonica A
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2008
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vol. 113
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issue 1
135-138
EN
Here we present the study of the stress dependence of the switching field in amorphous glass-coated magnetic microwire of composition FeNiMoB. Samples were heat treated in the temperature range from 250°C up to 500°C in order to obtain relaxed and nanocrystalline state. As-cast microwire shows strong stress dependence of the switching field, which decreases with the temperature of annealing. The sample is almost not stress dependent after heat treatment at 425°C, because the magnetostriction vanishes. However, the strongest stress dependence was found for the microwire annealed at 400°C, just below the optimal annealing temperature to obtain the nanocrystalline state.
20
Content available remote

Magnetic and Structural Characterization of NiXSb (X = Mn, Cr) Heusler Ribbon

62%
Ryba T., Vargova Z., Ilkovic S., Reiffers M., Kravcak J., Gyepes R., Varga R.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
857-859
EN
Half-Heusler alloys with composition NiMnSb and NiCrSb have been prepared by rapid-quenching method. NiMnSb half-Heusler alloy is characterized by single phase C1_{b} with polycrystalline structure while crystalline structure of NiCrSb shows multiphase system. Magnetic measurements indicated high anisotropy and easy magnetization direction in the parallel direction with respect to ribbon axis for NiMnSb alloy while paramagnetic behavior appears for NiCrSb alloy down to 50 K.
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