Search

Magnetic refrigeration (MR) based on the magnetocaloric effect (MCE) has been recognized as an environmentally benign and energy-efficient cooling technology. Exploring suitable magnetocaloric materials is a crucial prerequisite for practical MR applications. We have herein provided a systematic investigation of the crystal structure, microstructure, electronic structure, magnetic phase transition, critical behavior, and MCE of the GdCoC compound featuring excellent cryogenic magnetocaloric performance by means of experimental determination and theoretical calculation. The GdCoC compound is crystallized in a simple layered tetragonal crystal structure with a P 4 2 / mmc space group and undergoes two successive ferromagnetic (FM) transitions along with a low-temperature weak antiferromagnetic (AFM) transition under low magnetic fields. Density functional theory calculations confirms the FM coupling of the Gd and Co intra-sublattice interactions, whereas AFM coupling for their inter-sublattice interaction. The magnetic transitions are merged in to one under high magnetic fields which has been confirmed to be second-order type and its critical behavior can be understood in the framework of tri-critical mean-field model, whereas the low-temperature weak AFM transition is belonging to the first-order type. The excellent magnetocaloric performance of the GdCoC compound was identified by the parameters of magnetic entropy change, adiabatic temperature change, temperature-averaged entropy change, relative cooling power, and refrigerant capacity, which are superior to most of the well-known magnetocaloric materials with similar working temperatures, making it attractive for practical cryogenic MR applications. [Display omitted] [ABSTRACT FROM AUTHOR]

The magnetocaloric effect (MCE) has been extensively studied in various magnetic solids, aiming to both facilitate practical applications in magnetic cooling and deepen our understanding these materials' intrinsic properties. This study presents a systematic investigation of Gd 2 Ti 2 O 7 oxide, characterized by a geometrically frustrated magnetic structure, focusing on its structural and magnetic characteristics through experimental analysis and theoretical calculations. Emphasis is placed on its magnetic phase transition (MPT) and magnetocaloric properties, scrutinizing temperatures as low as 0.4 K and magnetic fields up to 16 T. The results reveal that Gd 2 Ti 2 O 7 oxide possesses a crystalline cubic pyrochlore-type structure with an antiferromagnetic (AFM) semiconductor ground state. The material undergoes a first-order MPT in low field and low-temperature regimes, transitioning to a second-order MPT above 2 K up to 16 T. Evaluation of magnetocaloric parameters, including maximum magnetic entropy change, temperature-averaged entropy change, relative cooling power, and refrigerant capacity, indicates moderate values under low magnetic field changes, while significantly large values are achievable under high magnetic field changes. This finding suggests that potential cryogenic magnetocaloric materials (MCMs) with optimal performance should exhibit low MPT temperatures induced by magnetic frustration and possess a ground state with a sufficiently large magnetic moment induced by low magnetic fields, thus avoiding excessively strong AFM coupling. This study lays the groundwork for future cryogenic MCM design and provides valuable insights into the intrinsic properties of geometrically frustrated magnetic materials. [Display omitted] [ABSTRACT FROM AUTHOR]

The magnetic refrigeration (MR) technology by utilizing the magnetocaloric (MC) effects of magnetic solids have been realized to be a promising energy efficiency and environmentally friendly technology. Developing or discovering proper magnetic solids with promising MC performances is one of the most important tasks at present stage since a huge gap still exists between the requirement of practical MR application and the MC performances of the magnetic solids. Herein, we reported a combined theoretical and experimental investigation of the crystal structure together with the magnetic properties, magnetic phase transition (MPT) and MC performances in Gd 2 MgTiO 6 oxide. The Gd 2 MgTiO 6 is confirmed to crystalize in a B -site ordered monoclinic double perovskite (DP) crystal structure. A rather unstable antiferromagnetic (AFM) interaction with large magnetic moment and semi-conductor characteristic with the band gap of 2.977 eV have been confirmed in Gd 2 TiMgO 6 DP oxide at ground state. Giant reversible cryogenic MC effect together with excellent MC performances have been confirmed by a series of the figure of merits including the values of maximum magnetic entropy change (-Δ S M) and refrigerant capacity (RC), which are evaluated to be 46.21 J/kgK and 300.27 J/kg around 3.3 K with the magnetic change of 0–7 T, these values are much better than most of the recently reported famous cryogenic MC materials and the commercialized magnetic refrigerants gadolinium gallium garnet (GGG) as well. The observed excellent MC performances suggest that Gd 2 TiMgO 6 DP oxide is a promising candidate material for cryogenic MR applications. Graphical abstract [Display omitted]. [ABSTRACT FROM AUTHOR]

Rare earth (RE) based RE - TM - X (TM = transition metal elements; X = P - block elements) materials have received continuous attention due to the exhibition of various intriguing magnetic functional characteristics. In this work, a combined experimental and theoretical investigation has been conducted in detail for RE Co 12 B 6 (RE = Ce, Pr, Nd) compounds with regard to their structural and magnetic properties, particularly the magnetocaloric effect and magnetic phase transition (MPT). All of the present RE Co 12 B 6 compounds are found to crystalize in the SrNi 12 B 6 -type structure and with a ferrimagnetic ground state, which is confirmed by density functional theory calculations and magnetization measurements. The magnetic moments of RE atoms and Co atoms tend to be in antiparallel alignment, and the MPT of these materials originates primarily from the spin-polarized 3 d electrons of the Co atoms, which can be greatly affected by the 4 f electrons of RE atoms. Considerable magnetocaloric effects have been observed around its own T C of 130, 157, and 160 K, for CeCo 12 B 6 , PrCo 12 B 6 , and NdCo 12 B 6 , respectively, which is related to a typical second-order MPT. The corresponding maximum magnetic entropy change and relative cooling power values,with field changes of 0–70 kOe, are determined to be 2.54, 2.84, and 2.77 J/kg K and 116.8, 156.2, and 155.1 J/kg, respectively. The MPT properties of present RE Co 12 B 6 compounds were studied in further detail by critical analysis using the modified Arrott Plot and Kouvel-Fisher methods, which can be explained within the frame of the 3D Heisenberg model with short-range magnetic interaction. [Display omitted] [ABSTRACT FROM AUTHOR]