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Magnetic and magnetocaloric effects of (Mn1-xFex)5Ge3 compounds are studied systematically. The maximum of magnetic entropy changes of 8.01 J/kg K under an external field change of 5 T is obtained for (Mn0.9Fe0.1)5Ge3, which is the largest value in Mn5Ge3-based solid solutions. Moreover, the Fe substitution increases the refrigeration capacity (RC) value greatly. The largest RC value of 237 J/kg in (Mn0.8Fe0.2)5Ge3 even compares favorably to that of many well-known magnetic refrigeration materials. Thus the Fe-containing (Mn1-xFex)5Ge3 compounds are much-improved magnetic refrigerants for the application of room-temperature magnetic refrigeration. The increase of the RC value is probably resulted from the formation of magnetic nanostructure. [ABSTRACT FROM AUTHOR]

La(Fe, Si)13 hydride is regarded as one of the most promising room-temperature refrigerants. However, to use the alloys in an active magnetic regenerator machine, it is vital to prepare thin refrigerants. In this work, a high H2 gas pressure of 50 MPa was employed to suppress the desorption of hydrogen atoms during the sintering process of plate-shaped La0.5Pr0.5Fe11.4Si1.6 hydrides. At 330K, a high-density sintered thin plate shows a large magnetic-entropy change ΔSm of 15.5 J/kgK (106mJ/cm³K) for a field change of 2T. The volumetric DSm is almost twice as large as that of bonded La(Fe,Si)13 hydrides. Favorably, hysteresis is almost absent due to the existence of micropores with a porosity of 0.69% which has been analyzed with high-resolution X-ray microtomography. [ABSTRACT FROM AUTHOR]

In the compound MnAs0.97P0.03, prepared by mechanical milling, a large microstrain of 0.68%, calculated by quantitative x-ray diffraction analysis, induces a recoverable helimagnetic state at low temperatures and suppresses the temperature/field-induced orthorhombic-hexagonal phase transition. This leads to a remarkable reduction of both the thermal and the magnetic hysteresis at the Curie temperature, TC. Around the helimagnetic-ferromagnetic transition temperature and at TC, a large inverse magnetocaloric effect (MCE) with magnetic entropy change ΔSm of 5.6 J/kg K at 208 K and a normal MCE with ΔSm of -4.4 J/kg K at 253 K for a 5 T field change are observed. After annealing, MnAs0.97P0.03 exhibits a large MCE near room temperature with ΔSm of ∼14 J/kg K for a field change from 0 to 5 T. [ABSTRACT FROM AUTHOR]

The structure and formation of nanoparticles without encapsulation of the intermetallic compound DyCo2 were investigated by using x-ray diffraction and high-resolution transmission electron microscopy. The DyCo2 nanoparticles are stable in air without any shell protection. A large magnetic-entropy change of 13.2 J kg-1 K-1 was found at 7.5 K in an applied-field change from 1 to 7 T, which is ascribed to the large magnetic moment density and the weak interaction energy in the nanoparticles. Such oxidation-resistant rare-earth transition-metal compound nanoparticles with large cryogenic magnetocaloric effect are useful for refrigeration applications at low temperatures. [ABSTRACT FROM AUTHOR]

A giant magnetocaloric effect was observed at room temperature in Mn1-xCrxAs compounds with x=0.006 and 0.01. The Cr dopant reduces (or even eliminates) the large thermal hysteresis of MnAs, while it lowers the first-order transition temperature from 313 K for MnAs to 265 K for Mn0.99Cr0.01As. Near the Curie temperature, a magnetic field induces a first-order phase transition from a ferromagnetic hexagonal phase to a paramagnetic orthorhombic phase, leading to a maximum value of ΔSM of 20.2 J/kg K at 267 K for a 5 T field change for Mn0.99Cr0.01As. The study on the Mn1-xCrxAs system may open an important field in searching proper materials for room-temperature magnetic refrigeration. [ABSTRACT FROM AUTHOR]

In Fe0.8Mn1.5As compound, an external magnetic field induces a metamagnetic transition from an antiferromagnetic phase to a ferrimagnetic phase above Ts=285 K, leading to large magnetocaloric effects around room temperature. Instead of showing inverse magnetocaloric effects, the sign of the entropy change ΔSM in the compound is unexpectedly negative, revealing a different mechanism. The maximum value of ΔSM is 6.2 J/kg K at 287.5 K for a magnetic field change of 5 T. The study on systems with antiferromagnetism-related metamagnetic transitions may open an important field in searching good materials for room-temperature magnetic refrigeration. [ABSTRACT FROM AUTHOR]