Excellent magnetocaloric properties of melt-extracted Gd-based amorphous microwires Appl. Phys. Lett. 101, 102407 (2012) Adiabatic magnetocaloric temperature change in polycrystalline gadolinium -A new approach highlighting reversibility AIP Advances 2, 032149 (2012) Ni59.0Mn23.5In17.5 Heusler alloy as the core of glass-coated microwires: Magnetic properties and magnetocaloric effect J. Appl. Phys. 112, 033905 (2012) Critical behavior and magnetocaloric effect of Gd65Mn35−xGex (x=0, 5, and 10) melt-spun ribbons

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Monte Carlo simulations were used for a detailed description of magnetic, martensitic and magnetocaloric properties of Ni2+x Mn1−x Ga (0.18 ⩽ x ⩽ 0.24) and Ni50Mn34In16 Heusler alloys, which undergo a first-order magnetostructural phase transition. In the simulations we made use of magnetic exchange parameters which were obtained by ab initio calculations. Results of magnetic and lattice contributions to the total specific heat as well as the change in the isothermal magnetic entropy ΔS mag and the adiabatic temperature ΔT ad changes around the magnetic and magnetostructural transitions in an external magnetic field agree fairly well with available experimental data.

The magnetocaloric effect (MCE) in an Fe48Rh52 alloy and Sm0.6Sr0.4MnO3 manganite was studied in cyclic magnetic fields. The adiabatic temperature change in the Fe48Rh52 alloy for a magnetic field change (ΔB) of 8 T and a frequency (f) of 0.13 Hz reaches the highest value of (ΔTad) of −20.2 K at 298 K. The magnitude of the MCE in Sm0.6Sr0.4MnO3 reaches ΔTad = 6.1 K at the same magnetic field change at 143 K. The temperature regions, where a strong MCE is exhibited in an alternating magnetic field, are bounded in both compounds. In the case of the Fe48Rh52 alloy, the temperature range for this phenomenon is bounded above by the ferromagnetic to antiferromagnetic transition temperature in the zero field condition during cooling. In the case of the Sm0.6Sr0.4MnO3 manganite, the temperature range for the MCE is bounded below by the ferromagnetic-paramagnetic transition temperature in zero field during heating. The presence of these phase boundaries is a consequence of the existence of areas of irreversible magnetic-field-induced phase transitions. It is found that the effect of long-term action of thousands of cycles of magnetization/demagnetization degrades the magnetocaloric properties of the Fe48Rh52 alloy. This can be explained by the gradual decrease in the size of the ferromagnetic domains and increasing role of the domain walls due to giant magnetostriction at the ferromagnetic to antiferromagnetic transition temperature. The initial magnetocaloric properties can be restored by heating of the material above their Curie temperature.

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Direct measurements of the magnetocaloric effect (MCE) in different materials (Gd, Fe48Rh52, Ni43Mn37.9In12.1Co7 and Ni2.07Co0.09Mn0.84Ga) in alternating magnetic fields with frequencies f ≤ 22 Hz and an amplitude ∆H = 6.2 kOe are carried out. The MCE in Gd shows inconsiderable changes with field frequency. Near paramagnetic-ferromagnetic phase transition in Ni43Mn37.9In12.1Co7 Heusler alloy a slight reduction of MCE with frequency is observed. In weak alternating fields in materials with AFM-FM magneto-structural phase transitions (Fe48Rh52, Ni43Mn37.9In12.1Co7) it is not possible to get a structural contribution to overall MCE because of irreversibility of the transitions in these fields. Near magnetostructural phase transitions the MCE in these alloys has only magnetic contribution, and does not show a significant dependence on the magnetic field frequency. In Ni2.07Co0.09Mn0.84Ga Heusler alloy the MCE vanishes at frequencies about 20 Hz. The obtained results show the increase of frequencies of operating cycles is one of the powerful methods to improve the efficiency of magnetic refrigerators in case of Gd as a refrigerant.

For the first time the magnetocaloric properties of La0.9Ag0.1MnO3, La0.8Ag0.2MnO3, La0.85Ag0.15MnO3, La0.8Ag0.15MnO3 and La0.8Ag0.1MnO3 manganites have been investigated by direct and indirect measurement techniques. All samples showed almost the same relative cooling power (RCP). Temperatures of maxima of the magnetocaloric effect (MCE) are between a few degrees below freezing and the room temperature region. The compounds showed RCP values of about 100 J kg−1 at a field change of 2.6 T, which is about half the RCP of gadolinium. Because of considerable MCE and the Curie temperatures ranging from 269 to 303 K, these materials could be used as magnetic refrigerants for magnetic refrigeration in the sub-room and room temperature range.

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