New Insight Into Magneto-Structural Phase Transitions In Layered Tbmn2ge2-Based Compounds

The Tb1-xYxMn2Ge2 series (x = 0, 0.1, 0.2) compounds are found to exhibit two magnetic phase transitions with decreasing temperature: from the paramagnetic state to the antiferromagnetic interlayer state at T-N(inter) and from an antiferromagnetic interlayer structure to a collinear ferrimagnetic interlayer structure at T-C(inter). Compared with the slight change of T-N(inter) (409 K, 410 K and 417 K for x = 0, 0.1 and 0.2 respectively), the replacement of Y for Tb leads to a significant decrease in T-C(inter) from 97.5 K for x = 0 to 74.6 K for x = 0.2. The variation in TC inter can be ascribed to the combination of two effects: (1) chemical pressure and (2) magnetic dilution effect by Y substitution for Tb. Besides, a strong anisotropic magnet-volume effect has been detected around T-C(inter) in all compounds with Delta a/a = 0.125%, 0.124% and 0.130% for x = 0, 0.1 and 0.2, respectively while no obvious effect is detected along the c-axis. The maximum magnetic entropy change were found to be -Delta S-max = 9.1 J kg(-1) K-1, 11.9 J kg(-1) K-1 and 6.3 J kg(-1) K-1 with a field change from 0 T to 5 T for x = 0, 0.1, 0.2 respectively.