Direct and inverse magnetocaloric effects in magnetostrictive GdMn2Ge2 with field-induced metamagnetic transition.

Heavy rare-earth-based ternary intermetallic compounds with the formula RT₂X₂ have drawn great interest because of their multiple magnetic transitions and various magnetic structures. Here, anisotropic magnetic behaviors, magnetocaloric effects (MCEs), and magnetostriction effects in single-crystalline GdMn₂Ge₂ are studied in two different directions. Experiments show a magnetic transition characterized by a sudden decrease in magnetization for μ₀H//a and a sharp increase for μ₀H//c at T_t. The transition is driven by lower temperatures for μ₀H//a, contrasting that for μ₀H//c with an increase in the magnetic field. An inverse MCE is observed for μ₀H//a with a maximum magnetic entropy change (− Δ S M max ) of −7.4 J kg⁻¹ K⁻¹ (μ₀ΔH = 6 T), while a direct MCE is obtained for μ₀H//c with an − Δ S M max of 8.0 J kg⁻¹ K⁻¹ under the same magnetic field change. Moreover, a remarkable field-induced metamagnetic transition and a magnetostriction effect are observed simultaneously at T_t, indicating strong magneto-lattice coupling. The T-μ₀H phase diagrams are constructed based on the magnetic properties. The coexistence of direct and inverse MCEs is discussed and is due to the spin-flop of Mn and anisotropic magnetic properties under magnetic fields in different directions. [ABSTRACT FROM AUTHOR]