Explore the vast range of titles available.

Magnetic and magnetocaloric effect (MCE) of the Er(Fe0.8−xMn0.2−yCox+y)2 Laves phase-type compounds have been investigated. X-ray diffraction (XRD) analysis has revealed that these compounds crystallize with the C15 type Laves phase structure (Space Group Fd-3m). The magnetization curves indicate a ferri-magnetic-ordering resulting of the antiparallel coupling between the moments of the heavy rare earth Er and the transition metal (TM). The partial substitution of Fe/Mn by Co increases the Curie temperature from 355 K for Er(Fe0.8Mn0.2)2 to 475, 550, and 555 K for Er(Fe0.7Mn0.2Co0.1)2, Er(Fe0.8Mn0.1Co0.1)2, and Er(Fe0.7Mn0.1Co0.2)2, respectively. According to the nature of the TM elements, arguments were presented forwards either Molecular Field or Spin Fluctuation Theory, even Stoner type pictures should be considered for. MCE was calculated according to the Maxwell relation based on isotherm magnetization measurements. The magnetic entropy change (−∆SM) observed on a 300–400 K temperature range can be understood in terms of a Spin Fluctuation Theory picture supported by both the different magnetic polarization levels that were shared by the TM elements and the related interatomic exchange forces.

The crystal structure and overall magnetic properties of RE(Fe0.25Co0.75)2Hy with RE = Ho and Er, were analyzed versus y, the hydrogen content. The single phase C15 type compounds, synthesized using cold crucible HF melting, were hydrogenated and controlled using a PCI apparatus. The impact of hydrogen insertion on the cell parameter, the Curie temperature TC and the magnetization saturation were determined. All compounds and hydrides were found to be ferrimagnets, the magnetic moment of RE and 3d elements being opposite since Ho and Er belong to the 2nd row of rare earth elements. Depending on the formula, a typical compensation point was in evidence. The 2nd order character of the ferri ↔ paramagnetic transition was established using the Arrott plot method. Magnetization isotherms vs. magnetic field gives quantified results for the magnetic entropy variation by application of the Maxwell relation. Control of y, the hydrogen content, shows it is interesting for improvement of the MCE of the starting compounds. However increasing y leads to decreased TC at the lowest temperatures, suggesting potential cryogenic uses.