Relationship between polymorphic structures and magnetic properties of La$_{2-x}A'_{x}$Ni$_{7}$ compounds ($A$' = Sm, Gd)

Valérie Paul-Boncour; Véronique Charbonnier; Nicolas Madern; Lotfi Bessais; Judith Monnier; Junxian Zhang

doi:10.1016/j.jmmm.2025.172859

paper

Relationship between polymorphic structures and magnetic properties of La $_{2 - x} A_{x}^{'}$ Ni $_{7}$ compounds ( $A$ ' = Sm, Gd)

arXiv:2502.02203 · doi:10.1016/j.jmmm.2025.172859

Abstract

In this study, the crystal structure and magnetic properties of La $_{2 - x} A_{x}^{'}$ Ni $_{7}$ compounds with magnetic rare earth elements ( $A$ ' = Sm, Gd) have been investigated combining X-ray powder diffraction and magnetic measurements. These intergrowth compounds crystallize in a mixture of 2 $H$ hexagonal (Ce $_{2}$ Ni $_{7}$ -type) and 3 $R$ rhombohedral (Gd $_{2}$ Co $_{7}$ -type) polymorphic structures which are related to the stacking of [ $A B_{5}$ ] and [ $A_{2} B_{4}$ ] subunits along the $c$ -axis.The average cell volume decreases linearly versus $A$ ' content, whereas the $c / a$ ratio reaches a minimum at $x$ = 1, due to geometric constraints upon $A$ ' for La substitution between the two different subunits. The magnetic properties strongly depend on the structure type and the $A$ ' content. Hexagonal La $_{2}$ Ni $_{7}$ is a weak antiferromagnet (wAFM) at low field and temperature and undergoes metamagnetic transitions towards weak ferromagnetic state (wFM) under applied field. Under an applied field of 0.1 T, La $_{2 - x} A_{x}^{'}$ Ni $_{7}$ intermetallic compounds display two different transition temperatures $T_{1}$ and $T_{2}$ that both increase with $x$ . $T_{1}$ is associated with a wFM-wAFM transition in the 2 $H$ phase for $A$ '= Sm, whereas $T_{2}$ is related to the Curie temperature of both 2 $H$ and 3 $R$ phases. A metamagnetic behaviour is observed between $T_{1}$ and $T_{2}$ with transition field $μ_{0} H_{T r an s}$ between 2 and 3.5 T for compounds with $A$ ' = Sm. The La $_{2 - x} S m_{x}$ Ni $_{7}$ compounds ( $x$ > 0} behave as hard magnets with a large coercive field $μ_{0} H_{C}$ at low temperature ( $μ_{0} H_{C}$ > 9 T at 5 K for $x$ = 2), whereas the La $_{2 - x} G d_{x}$ Ni $_{7}$ compounds ( $x$ > 0) are soft ferrimagnets with a linear increase of the saturation magnetization versus Gd content.

29 pages (20 main article, 9 in supplementary Material, 1 table, 19 figures (10 in main article, 9 in supplementary Material)

Relationship between polymorphic structures and magnetic properties of La2−x​Ax′​Ni7​ compounds (A' = Sm, Gd)

Abstract

References in corpus (7)

Relationship between polymorphic structures and magnetic properties of La $_{2 - x} A_{x}^{'}$ Ni $_{7}$ compounds ( $A$ ' = Sm, Gd)