Propriedades estruturais e magnéticas das ligas intermetálicas GdAgGa, TbMn2Si2 e Ni50Mn35In15: efeito da desordem e/ou redução do tamanho de partícula

Abstract

This study aimed to investigate the structural and magnetic properties of the intermetallic compounds GdAgGa, TbMn2Si2, and the Heusler alloy Ni50Mn35In15, focusing on the different relevant aspects of each material. The systems were synthesized by arc melting, with the TbMn2Si2 and Ni50Mn35In15 also undergoing processing for particle size reduction. Subsequently, they were characterized using X-ray diffraction, magnetization, and specific

heat techniques. The results indicated that structural disorder due to randomness in the non- magnetic site induces a complex magnetic state with the coexistence of long-range

ferromagnetic order and a reentrant spin-glass phase for the GdAgGa compound. A significant magnetocaloric effect was observed with a maximum magnetic entropy change of ~7 J/kg.K at ΔH= 50 kOe. High-energy milling in the TbMn2Si2 system reduces crystallite size and increases atomic disorder, i.e., defects, amorphization, etc. A weakening of exchange interactions leads to a decline in magnetization at high magnetic fields, while disorder broadens the magnetic transitions. Thermally annealed particles exhibit a significant exchange bias effect, which suggests changes in the interaction between magnetic moments at the interface of the ferromagnetic and antiferromagnetic lattices. On the other hand, thermally annealed Heusler alloy Ni50Mn35In15 microparticles (diameter ≤ 0.25 mm) stabilize the austenite phase at low temperatures. The combination of mechanical and thermal energy suppresses the structural transformation, which drives the magnetic properties of this alloy. These results highlight that the microstructural characteristics of the material are crucial for its magnetic properties. Therefore, the atomic disorders and specific treatments applied to the materials tune the Ni50Mn35In15 alloy martensitic transformation temperatures and effectively improve the exchange bias effect in the TbMn2Si2 system, confirming the importance of microstructure for the magnetic functionality of the studied compounds.