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Recently, superconductivity at high temperatures is observed in bulk La₃Ni₂O_7−δunder high pressure. However, the attainment of high‐purity La₃Ni₂O_7−δsingle crystals remains a formidable challenge. Here, the crystal structure and physical properties of single crystals of Sr‐doped La₃Ni₂O₇synthesized at high pressure (20 GPa) and high temperature (1400 °C) are reported. Through single crystal X‐ray diffraction, it is shown that high‐pressure‐synthesized paramagnetic Sr‐doped La₃Ni₂O₇crystallizes in an orthorhombic structure with Ni─O─Ni bond angles of 173.4(2)° out‐of‐plane and 175.0(2)°and 176.7(2)°in plane. The substitution of Sr alters in band filling and the ratio of Ni²⁺/Ni³⁺in Sr‐doped La₃Ni₂O₇, aligning them with those of “La₃Ni₂O_7.05”, thereby leading to significant modifications in properties under high pressure relative to the unsubstituted parent phase. At ambient pressure, Sr‐doped La₃Ni₂O₇exhibits insulating properties, and the conductivity increases as pressure goes up to 10 GPa. However, upon further increasing pressure beyond 10.7 GPa, Sr‐doped La₃Ni₂O₇transits back from a metal‐like behavior to an insulator. The insulator–metal–insulator trend under high pressure dramatically differs from the behavior of the parent compound La₃Ni₂O_7−δ, despite their similar behavior in the low‐pressure regime. These experimental results underscore the considerable challenge in achieving superconductivity in nickelates.

Topological kagome magnets RMn₆Sn₆(R = rare earth element) attract numerous interests due to their non-trivial band topology and room-temperature magnetism. Here, we report a high entropy version of kagome magnet, (Gd_0.38Tb_0.27Dy_0.20Ho_0.15)Mn₆Sn₆. Such a high entropy material exhibits multiple spin reorientation transitions, which is not seen in all the related parent compounds and can be understood in terms of competing magnetic interactions enabled by high entropy. Furthermore, we also observed an intrinsic anomalous Hall effect, indicating that the high entropy phase preserves the non-trivial band topology. These results suggest that high entropy may provide a route to engineer the magnetic structure and expand the horizon of topological materials.