The Development Of Gd-based Amorphous Composites And Researching Their Magnetocaloric Effect

Compared with gas compression refrigeration,magnetic refrigeration is a promising green refrigeration technology with the advantages of environmentally friendly,small volume,noise-free and high efficiency.The magnetic refrigeration based on the magnetocaloric effect,so it is greatly significant to develop magnetic materials with excellent magnetocaloric performance.According to the microstructure classification,the existing magnetocaloric materials mainly include crystalline materials and amorphous materials.Compared with crystalline magnetocaloric materials,amorphous magnetocaloric materials have a wider working temperature range,but the single-phase materials are still difficult to meet the requirement that refrigerating from room temperature to ultra-low temperature?such as liquid nitrogen temperature?.Therefore,in this article,the nanocrystalline phases are added into the Gd-based amorphous alloy by optimizing the alloy composition and adjusting the preparation process.Various Gd-based amorphous/nanocrystalline composite materials were prepared,and their magnetocaloric properties were studied.Firstly,the Gd_90-xNi_xAl₁₀?x=5,10,15?alloys with high Gd content were prepared into microfibers with multiple Gd crystal phases and Gd-based amorphous phase.With the increase of Gd content,the Gd phase increase and the Gd-based metallic glass phase decrease,when the composition is Gd₈₀Ni₁₀Al₁₀,the ratio of amorphous phase to Gd crystal phase is 1 to 1,and the magnetocaloric performance is optimized.The composite of the amorphous phase and the crystalline phases make the temperature dependency of magnetic entropy change of Gd₈₀Ni₁₀Al₁₀ composite microfiber is a bimodal shape,and its working temperature range is more than 200 K,which is suitable for the magnetic refrigeration from room temperature to liquid nitrogen temperature.The peak value of magnetic entropy change and refrigerant capacity of Gd₈₀Ni₁₀Al₁₀ are 6.15 Jkg^-1K^-1 and 985 Jkg^-1 respectively,at a field change of 5 T,which obviously exceed other magnetocaloric materials.Furthermore,the magnetic domain structures of Gd₈₀Ni₁₀Al₁₀ were studied by Lorentz Transmission Electron Microscope?LTEM?,the magnetic domain structure of[Gd Al]phases near220 K were discovered.The[Gd Al]phases improve the magnetic entropy change between the two magnetic entropy change peaks of the Gd₈₀Ni₁₀Al₁₀composite microfiber,which caused the large working temperature range and large refrigerant capacity of Gd₈₀Ni₁₀Al₁₀ composite material.Furthermore,the Gd₈₀Cu₁₀Al₁₀,Gd₈₀Mn₁₀Al₁₀,Gd₈₅Si₁₅,Gd₈₅Ni₁₅,Gd₈₅Co₁₅,Gd₆₈Cu₃₂,Gd₇₃Fe₂₇,Gd₈₅Ho₁₅,Gd₈₅Er₁₅ and Gd₈₅La₁₅ alloys were developed.The study showed that most of the high Gd content alloys show two peak in the magnetic entropy change curves?two Curie temperatures?.As the doping elements are different,the Curie temperatures of the composite are different,the difference value between two Curie temperature of the Gd₈₀Cu₁₀Al₁₀,Gd₈₀Mn₁₀Al₁₀ and Gd₆₈Cu₃₂ alloys are130 K,which is shorter than other composites.What's more,the Er₄₅Cu₄₅Al₁₀ metallic glass composite is developed,the entropy change normalized to the rare earth elements for this Er₄₅Cu₄₅Al₁₀ alloy is much higher than other Er-based metallic glasses because the Er-Cu composite does not contain Fe,Co,Ni element,these element will decrease the magnetocaloric effect of Er atoms because of the antiferromagnetic coupling.This finding is meaningful for the commercialization of rare earth-based metallic glass alloys in the magnetic refrigeration.Finally,the structure and magnetocaloric effect of Gd₈₅Al₁₅ were adjusted by applying a magnetic field in the melt spinning process.The study found that the degree of crystallization of the ribbon was significantly reduced in the applied magnetic field.When the applied magnetic field is 60 m T,the magnetic entropy change of the Gd₈₅Al₁₅ ribbon is markedly improved in the whole working temperature range and the peak value of magnetic entropy change curves has risen to6.58 Jkg^-1K^-1.