Magnetic ordering and table-like magnetocaloric effect in the hydrogen liquefaction region for Tb2Co(Si,Ge)2

The investigation and understanding of the magnetic complexity in magnetic refrigeration candidates is crucial for a better search of new materials. This work investigates the magnetic ordering and magnetocaloric properties of Sc 2 CoSi 2 -type Tb 2 CoGe 2 and Tb 2 CoSi 2 intermetallic compounds. Through detailed magnetic measurements and neutron diffraction analysis, the study clarifies the impact of Si−Ge substitution on microscopic magnetic structures and macroscopic magnetocaloric performance. The substitution of Si by Ge leads to an expansion of the unit cell and strongly alters the magnetic behaviour. Tb 2 CoSi 2 shows a high temperature paramagnetic (PM) to ferromagnetic (FM) transition at T C =198 K, a lower temperature spin reorientation transition at T m = 75 K and an antiferromagnetic (AFM) transition at T N = 13 K. In contrast, Tb 2 CoGe 2 undergoes a PM to AFM transition at a significantly lower temperature, T N =126 K, before evolving into an F M -like state at T M =66 K. Neutron diffraction confirms that Tb 2 CoSi 2 is an ac -plane collinear ferromagnet below T C , while Tb 2 CoGe 2 is an ac -plane collinear antiferromagnet below T N . Tb 2 CoGe 2 exhibits a metamagnetic transition from the antiferromagnetic state to a mixed collinear FM+AFM state upon application of an external magnetic field. Both compounds display a highly desirable table-like magnetocaloric effect over a wide temperature range, suitable for magnetic refrigeration applications in the N 2 and H 2 gas liquefaction regions. These findings emphasize that Si−Ge substitution is an effective mechanism for tuning magnetic properties in this intermetallic family in order to optimize their performance for magnetic refrigeration. • Tb 2 CoSi 2 and Tb 2 CoGe 2 magnetic and magnetocaloric properties studied. • Neutron diffraction reveals magnetic structures and Si-Ge substitution impact. • Tb 2 CoGe 2 shows a metamagnetic transition from AFM to mixed FM+AFM state. • Both compounds display a table-like magnetocaloric effect for gas liquefaction. • Si-Ge substitution effectively tunes magnetic order and refrigeration performance.