Crystal structure and physical properties of Yb 2 In and Eu 2-x Yb x In alloys

François Guillou (1) , H. Yibole (1) , Radia Hamane (2) , V. Hardy (2) , Y. B. Sun (1) , J. J. Zhao (1) , Y. Mudryk (3) , V. K. Pecharsky (3)

1 Inner Mongolia Normal University [Hohhot]
2 CRISMAT - Laboratoire de cristallographie et sciences des matériaux
3 ISU - Iowa State University

While binary RE 2 In, where RE = rare earth, have been reported a few decades ago, recent investigations revealed intriguing new physical insights. For instance, the discovery of a nearly ideal first-order ferromagnetic transition in Eu 2 In calls for further exploration of structures and properties of RE 2 In, in particular for the leastdocumented RE = Eu and Yb cases. Here, we investigate Eu 2-x Yb x In pseudobinaries with nominal values of x = 0.25, 0.5, 0.75, 1, 1.5, 2 by powder x-ray diffraction (including as function of temperature from 100 to 375 K for Yb 2 In), magnetization (5-300 K), as well as electrical resistivity (5-300 K) and calorimetric (2-150 K) measurements for Yb 2 In. Compared to other RE, Yb or Eu always raise challenging questions linked to their valence states. From average atomic volume, Yb is anticipated to be divalent in Yb 2 In, at least between 100 and 375 K, which is in line with the absence of 4 f magnetism. In agreement with x-ray diffraction and magnetization data, the resistivity of Yb 2 In is rather featureless and typical of a metal. Establishing Yb 2 In as a nonmagnetic isostructural reference for Eu 2 In allows one to use its heat capacity to revisit that of the latter, and get experimental insights into the exceptional magnetocaloric effect of the compound with Eu. In particular, we show that a third of the total magnetic entropy (S m ≈ 35.6 J mol −1 K −1 at T = 100 K) is concentrated in a 3 K temperature window around the T C of Eu 2 In. Starting from the ferromagnetic compound Eu 2 In [T C = 55.2(5) K], we show that Yb substitutions in Eu 2-x Yb x In lead to a decrease in both the Curie temperature [T C = 41(2) and 32(2) K for x = 0.25 and 0.5] and magnetic saturation, while weakening the first-order character of the transition as x increases. A significant isothermal entropy change of 5.1(4) J mol −1 K −1 for B = 2 T is found at 44 K in Eu 1.75 Yb 0.25 In, demonstrating that the giant magnetocaloric effect of Eu 2 In can be tuned to lower temperatures by Yb substitutions.

Mots clés: Magnetic phase transitions; Magnetism; Magnetocaloric effect; Specific heat; Rare-earth alloys

Domaines: Physique [physics]

François Guillou, H. Yibole, Radia Hamane, V. Hardy, Y. B. Sun, et al.. Crystal structure and physical properties of Yb 2 In and Eu 2-x Yb x In alloys. Physical Review Materials, 2020, 4, pp.104402. ⟨10.1103/PhysRevMaterials.4.104402⟩. ⟨hal-03022296⟩