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

• DOI: 10.48550/arxiv.2502.02203
• Publication Date: 2025-02-04
• Authors: Valérie Paul-Boncour; Véronique Charbon...; Nicolas Madern; Lotfi Bessais; Judith Monnier; J. B. Zhang
• Keywords: Condensed Matter - Materials Science; Intermetallic compounds Intergrowth compounds polymorphic structures metamagnetism ferrimagnetism; Intermetallic compounds; [CHIM] Chemical Sciences; Intergrowth compounds; [CHIM]Chemical Sciences; 500; Materials Science (cond-mat.mtrl-sci); FOS: Physical sciences; polymorphic structures; metamagnetism; ferrimagnetism

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