BORREGO MORO , Josefa María

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The FeCoSiAlGaPCB alloys can be prepared as bulk amorphous materials, with outstanding mechanical properties and increased electrical resistivity. These features can be beneficial for their application as a magnetic refrigerant. The influence of Co addition on the magnetic entropy change of the alloy has been studied. This compositional...

A Mössbauer spectrometry and magnetic study have been performed on FeCoSiAlGaPCB amorphous alloys in order to get information about the variations in the atomic short range order with the substitution of Fe by Co. The decrease of the Curie temperature with decreasing Fe content was analyzed in the framework of the molecular field theory. The...

Multicomponent Fe65.5Cr4Mo4Ga4P12C5B5.5 amorphous alloy is known to have good soft magnetic properties combined with large glass-forming ability. Searching for a nanocrystalline structure that could improve its magnetic properties, Cr and Mo were partially substituted by Cu. The devitrification process of Cu-containing alloys shows an...

The glass-forming ability of ( Fe x Co y B z C u ) 80 Si 3 Al 5 Ga 2 P 10 with x 5 5 – 70, y 5 0 – 63, z 5 5 – 12, and u 5 0 – 5 amorphous alloys has been analyzed in terms of the width of the supercooled liquid region, the reduced glass transition temperature, and the Vogel–Fulcher–Tammann parameters. Substitution of Fe by Co slightly ...

The onset of melting of standard samples, ascribed to surface melting, is generally used for calibration of calorimeters. However, in non-isothermal conditions, nucleation-driven volume melting, which is thermally activated, takes place. In this work, we propose an approximation in the frame of the classical nucleation and growth transformation...

The magnetocaloric effect of the FeCrMoCuGaPCB alloy series, suitable for being prepared as bulk amorphous alloys, has been studied. Optimal refrigeration cycles have a cold reservoir close to room temperature. The refrigerant capacity of these alloys is comparable to that of a Mo-containing Finemet-type alloy and is 40% bigger than that of...

X-ray diffraction, Mössbauer spectrometry and magnetic properties have been performed on FeGa arc-melted binary alloys in order to study the compositional dependence of the structural ordering and magnetic properties of these alloys. The average magnetic hyperfine field at 300 K decreases with increasing Ga content as does the average magnetic...

The non-isothermal kinetics of primary crystallization processes is studied from numerically generated curves and their predictions have been tested in several nanocrystallization processes. Single processes and transformations involving two overlapped processes in a non-isothermal regime have been generated and deviations from isokinetic...

The kinetics of the glass transition and the crystallization process of Co 62 2 x Fe x Nb 6 Zr 2 B 30 ( x 5 0,16) amorphous alloys with large supercooled liquid region was investigated by differential scanning calorimetry. The dependence of the glass transition on the heating rate was analyzed in terms of the Vogel–Fulcher–Tamman...

The influence of the Co content on the microstructure and magnetic behaviour of a series of amorphous and nanocrystalline (FeCo) 79Mo8Cu1B12 alloys is reported. Changes in the magnetic properties provoked by the microstructural evolution upon different thermal treatments of as-cast samples are analyzed as well. Kinetics of nanocrystallization...

We have analyzed the overgrowth problem arising in decelerated growth processes of spherical crystals in the frame of classical nucleation and growth theory developed by Kolmogorov, Johnson and Mehl, and Avrami (KJMA). To do that, simulations of decelerated growth transformations with a constant nucleation rate have been performed, changing the...

Optimizing the performance of magnetocaloric materials is facilitated by understanding the thermomagnetic transitions they undergo, including the order of these transitions and their strength. Those exhibiting strong first-order phase transitions (FOPT) are accompanied by large heating and cooling responses but with relatively small cyclic...

The influence of different compositional modifications on the magnetic entropy change and refrigerant capacity of Finemet, Nanoperm, HiTperm, and bulk amorphous alloys is presented. For all the studied alloys, the field dependence of the magnetic entropy change exhibits a quadratic dependence in the paramagnetic regime, a linear dependence in...

Amorphous Fe75Nb10B15 and (Fe70Co30)75Nb10B15 alloys were prepared by mechanical alloying from the elemental constituents and hot compacted at different temperatures within the supercooled liquid region. After compaction, the microstructure studied by X-ray diffraction shows an increase in the crystalline fraction for both compositions....

The structural relaxation of multicomponent Fe(Co)SiAlGaPCB amorphous alloys was investigated calorimetrically for annealed samples over a wide temperature range below the glass transition temperature. Upon heating, the annealed samples exhibit an endothermic reaction (enthalpy relaxation) starting around the annealing temperature and...

Amorphous samples of nominal composition Co62Nb6Zr2B30 have been prepared using mechanical alloying (MA) and rapid quenching (RQ) techniques. Differences appear in Curie temperature and the phases developed after crystallization. Refrigerant capacity is enhanced 20% in the MA-sample with respect to that of RQ-sample. Neglecting the...

The magnetocaloric effect of La(Fe,Si)13 samples deteriorates with the presence of secondary phases. However, it is highly challenging to produce single phase samples by conventional procedures and purification requires long annealing time. We propose grinding and particle size selection of non-optimal starting samples as procedure to enhance...

Fe75Nb10B15 alloys were prepared by mechanical alloying using different boron powders (crystalline B, commercial amorphous B, optimized amorphous B and intermetallic FeB) in the initial mixture, in order to study the boron incorporation into the Fe matrix and its influence on the amorphization of the alloys. Another composition with the same...

Gas-atomized Mn54Al46 particles constituted nominally of only ε- and γ2-phases, i.e. no content of the ferromagnetic L10-type τ-phase, have been used to study the evolution of phases during short time of high-energy milling and subsequent annealing. Milling for 3 min is sufficient to begin formation of the τ-MnAl phase. A large coercivity of...