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1
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New Approach to the Phenomenology of Amorphous Curie-Point Relaxation

100%
Lovas A.
|
|
issue 5
770-772
EN
The possible origin of short range atomic displacements coupled with the irreversible amorphous Curie temperature relaxation (Δ T_{C}^{am}) in Fe-based glasses is discussed and analyzed on the basis of quenched-in phase reminiscences. The displacements are dominantly symmetry changes, which are governed by the relative stability of fcc and bcc quenched-in phase reminiscences at a given temperature range. Those of elements which cause positive Δ T_{C}^{am} in as quenched state, also cause positive irreversible Δ T_{C}^{am} during structural relaxation. The influence of Cr addition is just the opposite in this respect.
2
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Anomalous Concentration Dependence of Amorphous Curie Temperature and the Thermopower in Ternary Fe-Cr-B Glasses

64%
Pál Z., Lovas A.
Acta Physica Polonica A
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2008
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vol. 113
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issue 1
139-142
EN
A non-monotonic compositional dependence of the amorphous Curie temperature (T_c^{am})) and of the thermopower (S) was found in Fe_{80-x}Cr_xB_{15} glassy samples. The significant change in the slope of concentration dependence of both properties lead to the conjecture of a hidden structural change in amorphous state. Similar anomalies were also observed earlier in the concentration dependence of microhardness in the same glasses, which clearly contradicts to the traditional homogeneous single phase concept of glassy state. The results are interpreted on the basis of the existence of quenched-in phase reminiscences (clusters) in these alloys inherited from the liquid state.
3
Content available remote

Wettability of Ceramic Substrates by Silver Based Alloys

64%
Weltsch Z., Lovas A.
Acta Physica Polonica A
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2013
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vol. 124
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issue 1
78-87
EN
The temperature dependence of wettability (wetting angle, Θp(T)) for Ag-based melts on graphite and Al_2O_3 substrates is compared. Typical alloying effects are found, as the Ag host metal is gradually replaced by various metallic elements. The essence of alloying lies in the change of the electron/atom (e/a) ratio. This ratio is also manifested in the shift of wetting angles on the same substrate. The effect is also supported by the calculations based on the rigid band model, and is also in qualitative agreement with the Hume-Rothery rules. Nevertheless, the effects are partially smeared by other (metallurgical) factors, like the interaction between the oxygen-alloying elements and by the graphite substrate-oxygen interaction. In contrast, such effects are not pronounced in the case of Al_2O_3 substrates. As a consequence, Θp(T) exhibits an opposite trend in the case of two substrates. Crossovers of the Θp(T) curves were often found. The positions of crossovers depend on the chemical character and concentration of solute atoms. Segregation and epitaxial texture formation after solidification were also observed in certain alloy drops, especially in high concentration range. This phenomenon is not yet explained in every detail.
4
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Evolution of Magnetic and Mechanical Properties in FINEMET-Type Precursor Glasses during Isothermal and Pulse Heat Treatments

51%
Hubač L., Novák L., Balla S., Lovas A.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
672-674
EN
The effects on the evolution of coercivity (H_c) and brittleness in FINEMET-type precursor glasses during traditional (isothermal) and pulse heat treatments are compared. The time and temperature dependences of these quantities are monitored during the series of isothermal and pulse heat treatments. The activation energy for H_c relaxation is lower than that for the brittleness evolution, however, dramatic changes in the values of these quantities can be detected above 300°C. Both quantities change mainly with temperature, they are less time-dependent.
5
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On the Mechanism of H-Induced Curie-Point Relaxation in Fe-Based Glassy Alloys

51%
Balla S., Kováč J., Novák L., Lovas A.
Acta Physica Polonica A
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2008
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vol. 113
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issue 1
55-59
EN
In Fe based glasses not solely the stress-sensitive magnetic properties, but also the amorphous Curie temperature (T_C^{am}) can be altered by hydrogen absorption or due to the low temperature "heat treatments" in liquid N_2 (-196°C). The sign and magnitude of this T_C^{am} shift is strongly compositional dependent, but it is also influenced by the thermal history of glasses (heat treatments). In this paper new experimental results are presented, which were obtained on FeCrB alloys, supporting the previous observations. An attempt of interpretation of the results is also made, which is based on the existence of the quenched-in phase reminiscences, being inherited from the liquid structure.
6
Content available remote

The Comparison of Hardness and Coercivity Evolution in Various Fe-B Based Glasses (Including FINEMET Precursor) during Relaxation and Crystallization

51%
Weltsch Z., Klam K., Lovas A.
Acta Physica Polonica A
|
2017
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vol. 131
|
issue 4
669-671
EN
Inverse relation exists between the hardness and coercivity change within the whole period of structural relaxation in the investigated Fe-B(Si) based metallic glasses. This relation is independent of B-content and composition. This inverse relation is no more valid in binary Fe-B glasses after the onset of crystallization, when both the hardness and coercivity exhibit rapid increase. In contrast, the inverse relation was in FINEMET type glasses between these properties preserved in the first step of crystallization during the whole period of nanocrystallization.
7
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Thermopower Monitoring of Relaxation and Devitrification in Fe-Based Glassy Alloys

51%
Lovas A., Kravcak J., Szabó A.
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vol. 126
|
issue 1
78-79
EN
The change of thermopower is investigated in Fe-based glassy alloys during structural relaxation and amorphous-crystalline transformation. It was found, that thermopower shifts to negative direction until solely the relaxation proceeds. This negative shift is composition independent. The net shape of thermopower curves is composed from the thermopower of the individual constituent crystalline phases after the crystallization process.
8
Content available remote

Pulse Heat Treatment of FINEMET Alloys Under Tension

51%
Lovas A., Hubač L., Novák L.
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vol. 126
|
issue 1
100-101
EN
In this contribution a less common experimental procedure is presented, which includes simultaneous application of electrical pulse heating, and longitudinal mechanical stress, applied along the ribbon length, for the magnetic property tailoring. The annealing is performed in protecting atmosphere in a vertical tube furnace by applying a weight at the free, cold bottom end of the ribbon. In these circumstances neither nanometer-size grains nor the concentration-distribution have been developed. The static coercive force, anisotropy and demagnetizing factor are monitored as a function of pulse number.
9
Content available remote

Thermopower and Surface Magnetic Characterization of Ni Thin Layers

39%
Szabo A., Varga R., Ujhelyi F., Komanicky V., Zorkovska A., Lovas A.
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vol. 126
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issue 1
204-205
EN
Thermoelectric power and surface magnetic characterization of Ni evaporated layers will be presented, with the comparison with the bulk Ni material. The bulk electrical and magnetic properties are developed gradually, approaching the bulk properties, as the layer thickness increases. Below the thickness of 180 nm, the evaporated layers are amorphous. The epitaxial stresses can appear in both, the anomaly observed in the thermopower and the surface coercivity measurements.
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