Magnetocaloric effect in Mn-containing Hitperm-type alloys.

The magnetocaloric effect of Fe60−xMnxCo18Nb6B16 x=0,2,4 is studied. Mn addition decreases the Curie temperature of the alloys but also reduces the peak entropy change and the refrigerant capacity of the material. The estimated adiabatic temperature change, for a maximum applied field of 15 kOe, is 1.3 K. Obtained values are comparable to those of some Nanoperm-type alloys. The magnetic entropy change, SM, of the studied samples follows a master curve, which is the same for all of them. The exponent controlling the field dependence of SM scales with reduced temperature in the same way as the master curve does

On the isothermal kinetics analysis of transformations in metastable systems. A combined use of isothermal and non-isothermal calorimetry

A procedure to optimize the isothermal calorimetric data of very slow transformation processes of metastable systems is proposed. The method uses an experimental baseline to identify the transitory effects due to the equipment. Moreover, the combined use of isothermal and non-isothermal results is shown to be effective to overcome the intrinsic problems of low signal and signal drift for such processes. The procedure has been applied to the analysis of the nanocrystallization kinetics of the Fe60Co18Nb6B16 alloy at different devitrification stages. Based on microstructural observations, an instantaneous growth approach was assumed and a phenomenological expression of the dependence of the nucleation frequency with both the transformed fraction and the temperature was obtaine

Nanocrystallization effects on the specific heat of fe-co-nb-b amorphous alloy

Specific heat at constant pressure, CP, was measured on amorphous, nanocrystalline and fully crystalline samples of Fe60Co18Nb6B16 alloy. Magnetic and calorimetric measurements agree, describing a continuously decreasing Curie temperature of the amorphous phase. A clear enhancement of CP over the Dulong-Pettit limit has been observed (from 14 to 25 %). Part of the enhancement is due to magnetic (mainly amorphous phase) and electronic contributions, although an excess volume can be inferred from the high value of the slope of CP versus temperatur