The magnetocaloric effect (MCE) is the basis for magnetic refrigeration, and can replace conventional gas compression technology due to its superior efficiency and environment friendliness. MCE materials must exhibit a large temperature variation in response to an adiabatic magnetic-field variation and a large isothermal entropic effect is also expected. In this respect, MnAs shows the colossal MCE, but the effect appears under high pressures. In this work, we report on the properties of Mn(1-x)Fe(x)As that exhibit the colossal effect at ambient pressure. The MCE peak varies from 285 K to 310 K depending on the Fe concentration. Although a large thermal hysteresis is observed, the colossal effect at ambient pressure brings layered magnetic regenerators with huge refrigerating power closer to practical applications around room temperature.

Magnetic refrigeration is a good alternative to gas compression technology due to higher efficiency and environmental concerns. Magnetocaloric materials must exhibit large adiabatic temperature variations and a large entropic effect. MnAs shows the colossal magnetocaloric effect under high pressures or with Fe doping. In this work the authors introduce a class of materials—Mn1−xCuxAs—revealing a peak colossal effect of −175J∕(Kkg) for a 5T field variation at 318K and ambient pressure.

Manganites have been attracted considerable attention due to some intriguing magnetic properties, such as magnetoresistance, spin glass behavior and superparamagnetism. In recent years, some studies point to the effect of particle size and dimensionality of these compounds in their magnetic features. Particularly, LaCaMnO material research is well explored concerning the bulk material. To overcome the lack of the information we successfully produced advanced nanostructures of La 0.6 Ca 0.4 MnO 3 manganites, namely nanotubes and nanoparticles by using a sol-gel modified method, to determine the size particle effect on the magnetism. The manganites crystal structure, magnetic and magnetocaloric properties were studied in a broad temperature range. Transmission electron microscopy revealed nanoparticles with sizes from 45 up to 223 nm, depending on the calcination temperature. It was found that the magnetic and magnetocaloric properties can be optimized by tuning the particle size; for instance, the magnetic transition broadening by decreasing the particle size. We report the relative cooling power (RCP) of these samples; it was found that the best RCP was observed for the 223 nm particle (508 J/Kg). Finally, this work contributes to the research on the magnetic properties and magnetocaloric potentials in nanostructured systems with distinct morphologies.

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In this work, we explore the magnetocaloric and magnetic properties of isoelectronic manganites R 0:6 Sr 0:4 MnO 3 (R ¼ La, Pr, Nd, and Sm). Upon substitution of La 3þ by smaller rare-earth ions, the average ionic radius hr A i of the A-site (A ¼ (R, Sr)) elements systematically decreases. It is found that, with decreasing hr A i, the magnetic-ordering temperature decreases from 341 K for La 0:6 Sr 0:4 MnO 3 to 126 K for Sm 0:6 Sr 0:4 MnO 3. Interestingly, the magnetic-entropy change increases with decreasing hr A i, reaching DS M ¼ À8:4 J=kg K for DH ¼ 0 À 20 kOe for Sm 0:6 Sr 0:4 MnO 3. For manganites, this is a high value of DS M , and it is related to the fact that the compound exhibits first-order magnetic transition. In contrast, the three other compounds exhibit a second order transition. The results indicate that the structural distortions caused by the decreasing hr A i couple the spin subsystem to the lattice, thus, inducing a first-order magnetic transition. V