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The partially overlapped ferroelastic/martensitic and para-ferromagnetic phase transitions of a Ni$_{50.53}$Mn${33.65}$In$_{15.82}$ metamagnetic shape memory alloy have been studied from calorimetric, magnetic and acoustic emission measurement. We have taken advantage of the existence of thermal hysteresis of the first order ferroelastic/martensitic phase transition ($\sim2.5$K) to discriminate the latent heat contribution $\Delta$Ht = 7.21(15) kJ/kg and the specific heat contribution $\Delta$Hc = 216(1) J/kg to the total excess enthalpy of the phase transition. The specific heat was found to follow a step-like behavior at this phase transition. The intermittent dynamics of the ferroelastic/martensitic transition has been characterized as a series of avalanches detected both from acoustic emission and calorimetric measurements. The energy distribution of these avalanche events was found to follow a power law with a characteristic energy exponent $\epsilon\sim2$ which is in agreement with the expected value for a system undergoing a symmetry change from cubic to monoclinic. Finally, the critical behavior of the para-ferromagnetic austenite phase transition that takes place at $\sim 311$K has been studied from the behavior of the specific heat. A critical exponent $\alpha\sim0.09$ has been obtained, which has been shown to be in agreement with previous values reported for Ni-Mn-Ga alloys but different from the critical divergence reported for pure Ni., Comment: 18 pages, 11 figures

Ribbons of a Ni55Fe19Ga26 Heusler alloy were prepared by melt spinning technique. The effect of pressure on magnetostructural transitions was studied comparing as-spun ribbons to ribbons previously submitted to an axial pressure and to powder obtained from manually grinded as-spun ribbons. The martensitic transformation present in the as-spun ribbon almost vanishes after pulverization. The structural change driven by mechanical treatment is a stress-induced intermartensitic transformation from a 14 M modulated to a non-modulated tetragonal (NM) structure. There is a progressive change from the structure of as-spun samples to that of the pulverized one in samples submitted to axial pressures as it increases.

Amorphous Fe-Zr and Fe-Nb alloys with 70 at.% Fe have been prepared by ball milling a mixture of elemental powders. The combination of Mössbauer spectroscopy, X-ray diffraction, scanning electron microscopy and differential scanning calorimetry techniques supplies detailed information about the composition as well as microstructural parameters of remaining crystalline and amorphous phases developed during milling. Detailed analysis of the Fe environments allows us to distinguish Fe atoms in paramagnetic sites between those incorporated to crystalline Zr or Nb rich phases and those Fe atoms in amorphous phase., This work was supported by the Spanish MINECO and EU FEDER (Project MAT 2013-45165-P), AEI/FEDER-UE (Project MAT-2016-77265-R) and the PAI of the Regional Government of Andalucía. A.F. Manchón-Gordón acknowledges a VPPI-US fellowship from University of Sevilla.

The magnetocaloric effect and its most straightforward application, magnetic refrigeration, are topics of current interest due to the potential improvement of energy efficiency of cooling and temperature control systems, in combination with other environmental benefits associated to a technology that does not rely on the compression/expansion of harmful gases. This review presents the fundamentals of the effect, the techniques for its measurement with consideration of possible artifacts found in the characterization of the samples, a comprehensive and comparative analysis of different magnetocaloric materials, as well as possible routes to improve their performance. An overview of the different magnetocaloric prototypes found in literature as well as alternative applications of the magnetocaloric effect for fundamental studies of phase transitions are also included., This work was supported by the Spanish MINECO (project MAT2013-45165-P), AEI/FEDER-UE (project MAT-2016-77265-R) and the PAI of the Regional Government of Andalucía. L.M. Moreno-Ramírez acknowledges a FPU fellowship from the Spanish MECD.

A model is proposed to describe the evolution of the amorphization process driven by mechanical grinding. This model considers the interface controlled growth of the disordered regions at the boundaries between the crystallites (unlike the classical nucleation and growth theory, the growing particles are thus concave which affects the kinetic equation). The validity of this model has been tested for the amorphization process of mechanically alloyed Fe-Nb-B system at different frequencies. Predictions of the model are in agreement with the experimental results and values of the linear growth rate and the thickness of the starting disordered layer are obtained., This work was supported by MINECO and EU FEDER (projects MAT2013-45165-P and MAT2016-77265-R) and the PAI of the Regional Government of Andalucía. MINECO/ICTI2013-2016/MAT2016-77265-R

Covellite, CuS and chalcocite, Cu2S nanoparticles prepared in the explosive manner from elemental precursors were further ball-milled in order to observe additional changes caused by mechanical action. Three phases of chalcocite were interchanging during milling, monoclinic one being major at the equilibrium after 30 min. In the case of covellite synthesis, milling for 15 min brought about a significant diminishment in the content of digenite, Cu1.8S, impurity. Covellite powder exhibited finer character than chalcocite, as documented by crystallite size, grain size and specific surface area analysis. Finally, the effect of milling speed on the explosive character of the reaction and phase composition of chalcocite was investigated. The most drastic conditions favored the formation of the monoclinic phase with the lowest symmetry and the time and intensity of the explosion was found to depend on the milling speed. The whole process is mechanically driven. Slovak Research Development Agency APVV-14-0103 Slovak Grant Agency VEGA 2/0027/14 Ministerio de Ciencia e Innovación MAT-2013- 45165-P, MAT-2016-77265-R German Federal Ministry of Education and Research IB-COMSTRUC-010

Structural relaxation in FeSiB–CuNb alloys is studied from enthalpic and Curie temperature effects. Enthalpy release and Curie temperature changes can be fitted to an exponential behaviour as a function of the annealing time by using two different relaxation times. For ribbons melt-spun at different wheel speed, no significant differences in structural relaxation behaviour are found.

Samples of FeCoNbBCu alloy were nanocrystallized under zero field annealing (ZF) and transverse field annealing (TF) conditions. A reduction in coercivity for TF samples with respect to ZF sample (16 and 45 A/m, respectively) is observed. Kerr microscopy images show a well-defined parallel domain structure, transversally oriented to the ribbon axis for the TF sample unlike for the ZF sample, for which a complex pattern is observed with large and small domains at the surface of the ribbon. Although Mössbauer spectra are clearly different for the two studied samples, Mössbauer studies confirm that there is no significant difference between the hyperfine field distributions of TF and ZF samples but only the relative intensity of the 2nd and 3rd lines A (related to the angle between the gamma radiation and the magnetic moments, α). However, for TF annealed samples α = 90 deg (A = 4), indicating that the magnetic moments lay on the plane of the ribbon in agreement with the well-defined domain structure observed by Kerr microscopy, ZF annealed samples show A = 1.8. This value is close to that of a random orientation (A = 2) but smaller, indicating a slight preference for out of plane orientations. Moreover, it is clearly smaller than that of the as-cast amorphous samples A = 2.8, with a preference to in-plane orientations. The application of the law of approach to saturation yields a larger effect of the inhomogeneities in ZF sample with respect to TF one., This work was supported by the Spanish Ministry of Science and Innovation and EU FEDER (Project MAT2013-45165-P), the PAI of the Regional Government of Andalucía, and the Slovak Projects APVV-0492-11, VEGA 2/0192/13. The Slovak team acknowledges also the support of the Operational Program “Research and Development” financed through European Regional Development Fund through the Projects ITMS 26220120019 and ITMS 26220220061.

In recent years, the magnetocaloric effect is studied not only for the search of potential magnetic refrigerant materials but also for the analysis of critical phenomena. In both cases, the demagnetizing field might have a notable influence on the results. In this work, we carry out a systematic study, based on theoretical simulations, of the influence of the demagnetizing factor on the magnetocaloric properties. On the one hand, we show that demagnetizing factor affects only slightly the magnetic entropy change ( D S M ), reducing its magnitude and shifting the peak to higher temperatures. On the other hand, it dramatically affects the exponent n of field dependence ð D S M / H n Þ at temperatures below the peak. We demonstrate that scaling of the magnetocaloric curves can be used to remove the influence of the demagnetizing field and, to which extent, critical exponent determination can be affected. Results of numerical simulations are compared with experimental data from a ball milled powder alloy.

Dynamical analysis of the movement of a single ball in a planetary ball mill yields a cubic law with the frequency of the mill for the power released during the process. This fact has been explored for two binary compositions (Fe70Zr30 and Fe70Nb30) using two different milling frequencies. The experimental techniques used, in general, support the predictions of the equivalent milling time model. However, some deviations appear which could be ascribed to differences in the temperature inside the vial during milling.

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 behavior are found when the overlapped processes have different activation energies. In the case of overlapped processes competing for the same type of atoms, the heating rate dependence of the obtained Avrami exponent can supply information on the activation energies of each individual processes. The application to experimental data of nanocrystallization processes is consistent with a limited growth approximation. In the case of preexisting crystallites in the as-cast samples, predictions on the heating rate dependence of the obtained Avrami exponents of multiple processes have been confirmed. Ministerio de Ciencia e Innovación MAT2010-20537 European Commission (EC). Fondo Europeo de Desarrollo Regional (FEDER) MAT2010-20537 Junta de Andalucía P10-FQM-6462 ESTEEM 026019

Mechanical alloying of Fe75Nb10B15 and Fe85Nb5B10 systems has been performed from an initial mixture of elemental powders. A bcc supersaturated solid solution is developed during milling for both alloys. However, Fe75Nb10B15 alloy also develops an amorphous phase, which amount increases with milling time. Milled powder samples were compacted at 7.7 GPa at different temperatures. Scanning electron microscopy images show that the presence of amorphous phase enhances the quality of compaction. Compaction at 823 K preserves both microstructure and magnetic properties of as-milled powders in both alloys. Compaction at 973 K affects mainly the crystalline fraction of the alloy with 10 at. % Nb. Compaction at 1273 K yields the formation of bcc Nb and fcc Fe23B6 phases, which magnetically harden the material.

X-ray diffraction patterns of mechanically alloyed Fe85Nb5B10 powder were fitted using whole powder pattern decomposition procedure to resemble the presence of α-Fe type crystals with different Nb content. To do so, a distribution of lattice parameters was proposed based on the asymmetry of the diffraction maxima and the broadening of the distribution of the powder particles composition. Analogously, a set of discrete sextets was used to represent the different local Fe environments. Gobierno de España MAT 2007-65227 European Commission. Fondo Europeo de Desarrollo Regional MAT 2007-65227 Junta de Andalucía P06-FQM-01823

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.

The oxidation behavior of FeCo(NbZr)B(Cu) alloy series was studied. After heating up to 1073 K, an oxide layer ∼ 1 μ m thick with a two-layer structure can be identified previous to a sharp interface between the oxide layer and alloy matrix, where no oxygen is detected. The coercivity of nanocrystallized samples increases, independently of the gas environment, during additional long-time-annealing without a significant change of the microstructure.

The partial substitutions of Co for Fe and Ge for B are studied for a Fe83 − xCoxZr6B10 − yGeyCu1 alloy series (x = 0, 5 and 20; y = 0 and 5) as a possible way of enhancing the high temperature applicability of NANOPERM alloys. The devitrification process, the nanocrystallization kinetics and the nanocrystalline microstructure are similar for all the studied alloys. Good soft magnetic properties are observed even at a high crystalline volume fraction of body-centered cubic α-Fe nanocrystals, which are stable up to ∼1000 K. The partial substitution of Co for Fe is very effective to increase the Curie temperature of the residual amorphous matrix ( T C AM ) . Although the substitution of Ge for B is ineffective to increase T C AM , a clear increase of the saturation magnetization with respect to the Ge-free alloy can be observed.