Antal Lovas

Magnetization and NMR study of amorphous Ni-P alloys in the paramagnetic concetration range

Abstract The temperature- and field-dependence of magnetization, and the 31 P NMR linewidth and Knight shift of some amorphous Ni 100− x P x alloys with 18⩽ x ⩽ 22 prepared by melt-quenching and electrodeposition were studied below room temperature. Although all the alloys investigated contain magnetic inhomogeneities, the amount and nature of which depend on impurities and on the details of sample preparation, it could be established that the amorphous matrix of Ni 100− x P x alloys with x ⩾ 18 exhibit Pauli paramagnetism and the Pauli susceptibility was found to decrease rapidly with P content. From the results, a similarity of the electronic structure and the short-range order in amorphous Ni-P alloys and in the crystalline Ni 3 P compound is deduced.

Alloying Effects on Wetting Ability of Diluted Ag-Based Melts on Ceramic Substrates

The wetting angles (Θ) of Ag-M based melts (M: Cd, Sn, Sb) on graphite and Al2O3 substrates are compared. Despite of the inert chemical character and the similar surface roughness of substrate materials, the wetting angle is smaller on the Al2O3. The compositional and concentration dependence of Θ exhibits similar trends, than that, observed in the bulk transport properties such as the specific electrical resistance or the thermopower obtained on the same alloys in solid state. No segregation effects can be detected on the solidified metal drops.

Tc measurement with high heating rate (100 K/s) on binary FeB glassy alloys

Abstract A high heating rate (100 K/s) was used for measuring T c using low frequency ac permeability in that concentration range of Feue5f8B where previously only extrapolation was possible. These measurements provide a clue to the origin of the data scattering found in the literature.

Compositional and Stress-Sensitive Factors during the Thermopower Characterization of Single Phase Crystalline and Glassy Alloys

For the study of stress state in engineering alloys, the thermopower (S) measurement could be acceptable method after a suitable calibration (fitting the S value to the change of well known other physical parameters like the magnetic coercive force, hardness or strength increase during various thermomechanical treatments). For this purpose a simple equipment is constructed and built by which the S shift can be measured versus the increasing mechanical tensile load. The first results will be published in this paper, obtained on various metallic glass ribbons.

Hydrogen-induced phase-separation in the amorphous Ni-Zr system

Abstract It is found that the magnetic state of the amorphous Ni 60 Zr 40 samples changes from paramagnetic to superparamagnetic upon hydriding. The density and the size of the magnetic clusters induced by the hydriding process was determined by magnetic and scanning transmission electron microscopic (STEM) measurements.

Structural relaxation in amorphous metallic glasses studied by the change of Curie temperature

Experimental results show that most of the physical properties of the metallic glass ribbons depend on the processing conditions. Here, the variation of Curie temperature will be investigated as a function of quenching conditions. Though these alterations are relatively small compared with the change obtained during structural relaxation, the quenched-in differences are conserved in the specimens even after high temperature annealing near the glass transition.

Wetting Ability of Ag Based Molten Alloys on Graphite Substrate

The wetting angle (Θ) of molten Ag (Zn, Cu, Ga) drops on graphite substrate is investigated. A texture formation was found in the substrate/drop interphase region after solidification. The enrichment (segregation) of Ag atoms in the interface layer was observed in the Ag-Cu alloy, and unexpected mixing between graphite substrate and the Ag-Ga melt was also detected in the solidified structure.

Viscous Phenomena in Magnetic and Thermal Properties of Fe-Ni-Based Glasses Induced by Cryo-Treatments

The influence of cryo-treatment is investigated according to some magnetic and thermal properties of Fe₄₀Ni₄₀Si₆B₁₄ glassy alloy. Saturation magnetization (M_S), amorphous Curie temperature (T_C ^am) heat capacity (C_p) and the width of crystallization exotherm peak were measured before and after the cryo-treatment. The treatment causes a very stable structural imprint in the investigated properties. Not all property changes are completely irreversible, however. The T_C ^am exhibits a very slow, viscous reconstruction during subsequent isothermal or cyclic heat treatments. The heat capacity of cryo-treated samples increases compared to the nontreated ones. Due to the low temperature treatment the kinetic of crystallization changes also, which is manifested in the shift of half width of crystallization peak. The magnitude of the LN treatment induced effects depends on the whole thermal history of the sample.

Change in soft magnetic properties of Fe-based metallic glasses during hydrogen absorption and desorption

The stress level can be altered in soft magnetic amorphous alloys by hydrogen absorption. The resulting changes in the soft magnetic parameters are reversible or irreversible, depending on the chemical composition. Some of these effects are demonstrated in Fe–B, Fe–W–B, and Fe–V–B glassy ribbons, in which various magnetic parameters are measured mainly during hydrogen desorption. The rate of hydrogen desorption is also monitored by measuring the pressure change in a hermetically closed bomb. The observed phenomena are interpreted on the basis of induced stresses and chemical interactions between the solute metal and hydrogen.

Influence of early stages of nanocrystallization on the low-temperature magnetic properties of nanocrystalline ribbons

Abstract A correlation was found between the change of the saturation magnetization ( M s ) and spin wave stiffness constant ( D sp ) as a function of annealing temperature for FINEMET-type glassy precursors (Fe 73.5 Nb 3 Si 13.5 B 9 Cu 1 ), annealed in the temperature range 400–540°C for times up to 1xa0h. During irreversible structural relaxation both M s and D sp increase. During the evolution of the nanocrystals M s decreases while D sp increases.