Field dependence of the adiabatic temperature change in second order phase transition materials: Application to Gd

The field dependence of the adiabatic temperature change Tad of second order phase transition materials is studied, both theoretically and experimentally. Using scaling laws, it is demonstrated that, at the Curie temperature, the field dependence of Tad is characterized by H1/. Therefore, as the magnetic entropy change SM follows a H(1−)/ power law, these two dependencies coincide only in the case of a mean field model. A phenomenological construction of a universal curve for Tad is presented, and its theoretical justification is also given. This universal curve can be used to predict the response of materials in different conditions not available in the laboratory (extrapolations in field or temperature), for enhancing the resolution of the data and as a simple screening procedure for the characterization of materialsThis work was supported by the Spanish Ministry of Science and Innovation and EU FEDER (Grant No. MAT 2007-65227), and the PAI of the Regional Government of Andalucía Grant No. P06-FQM-01823 .Peer reviewe

Magnetothermal properties of molecule-based materials

We critically review recent results obtained by studying the low-temperature specific heat of some of the most popular molecular magnets. Perspectives of this field are discussed as well.Comment: 12 pages text + 14 pages figures, Submitted as "feature article" to Journal of Materials Chemistr

Reducing extrinsic hysteresis in first-order La(Fe,Co,Si)13 magnetocaloric systems

Reducing extrinsic hysteresis in first-order la (Fe,Co,Si)13 magnetocaloric system

A Dense Metal-Organic Framework for Enhanced Magnetic Refrigeration

The magnetocaloric effect of gadolinium formate, Gd(OOCH)3, is experimentally determined down to sub-Kelvin temperatures by direct and indirect methods. This 3D metal-organic framework material is characterized by a relatively compact crystal lattice of weakly interacting Gd3+ spin centers interconnected via light formate ligands, overall providing a remarkably large magnetic:non-magnetic elemental weight ratio. The resulting volumetric magnetic entropy change is decidedly superior in Gd(OOCH)3 than in the best known magnetic refrigerant materials for liquid-helium temperatures and low-moderate applied fields.Comment: 11 pages, 4 figure

Review on the developments of active magnetic regenerator refrigerators – Evaluated by performance

© 2020 Magnetic/magnetocaloric refrigeration is an energy-efficient and environmentally safer cooling technology with the potential to be an alternative to conventional vapor compression systems in the future. Magnetocaloric effect (MCE) is a measure of relative temperature rise/drop of certain ferromagnetic materials upon the application/removal of a magnetic field. The technology uses MCE of some materials such as Gd to produce temperature difference/span relative to the ambient via a four-stage regenerative cycle known as active magnetic regenerative (AMR) cycle. Research in this area has been thriving especially during the last two decades focussing on different aspects of technology such as materials, magnetic field sources, and system design. On the system design, studies investigating the effect of different magnetic, thermal-hydraulic, and geometric parameters on the performance have been found in the literature. The present work offers a chronological review and comparison of recent advances in AMR refrigerators. Findings and results reported in the literature are compared in terms of magnetocaloric materials, geometric parameters (such as regenerator geometry); operating parameters e.g. cycle frequency, utilization, heat transfer fluid, heat rejection temperature, and cooling load, etc. Besides, performance indicators such as no-load temperature span, cooling capacity, and/or system coefficient of performance have been considered. Parametric sensitivity and performance trends have been identified and discussed. Major barriers to achieving system peak performance and hence the marketability of the technology are also highlighted

Field dependence of the adiabatic temperature change in second order phase transition materials: Application to Gd

The field dependence of the adiabatic temperature change Tad of second order phase transition materials is studied, both theoretically and experimentally. Using scaling laws, it is demonstrated that, at the Curie temperature, the field dependence of Tad is characterized by H1/. Therefore, as the magnetic entropy change SM follows a H(1−)/ power law, these two dependencies coincide only in the case of a mean field model. A phenomenological construction of a universal curve for Tad is presented, and its theoretical justification is also given. This universal curve can be used to predict the response of materials in different conditions not available in the laboratory (extrapolations in field or temperature), for enhancing the resolution of the data and as a simple screening procedure for the characterization of materialsThis work was supported by the Spanish Ministry of Science and Innovation and EU FEDER (Grant No. MAT 2007-65227), and the PAI of the Regional Government of Andalucía Grant No. P06-FQM-01823 .Peer reviewe

Pressure influence of magnetic properties of crystalline compounds and amorphous alloys of heavy rare-earth metals with iron

R_2Fe_1_7 (R=Y, Er, Dy), amorphous alloys R_xFe_1_-_x (R=Er, Dy, Ho, Y, To) (0,25<x>0,6) are considered in the paper aiming at the investigation of the influence of the high hydrostatic pressure (to 10"1"0 dynexcm"-"2) on the magnetization and magnetic phase transitions. As a result the magnetization modification under the pressure has been established. The dependence of integrals of exchanging interaction RZM-Fe and Fe-Fe on the atomic volume has been determined. Compounds and amorphous alloys, possesing the abnormal high values of the volumetric magnetization (to 400x10"-"6) have been obtainedAvailable from VNTIC / VNTIC - Scientific & Technical Information Centre of RussiaSIGLERURussian Federatio