Magnetic and electrical properties of La 2-x Bi x NiMnO 6 (0.2 ≤ x ≤ 1.0) synthesized at high-temperature and high-pressure

Polycrystalline La _2 − x Bi _x NiMnO ₆ (x = 0.2, 0.5, 1.0) samples were synthesized via a high-temperature and high-pressure method, with their structural, magnetic, and electrical properties systematically characterized. X-ray diffraction confirms a monoclinic double perovskite structure (space group P2 ₁ /n) for all samples, while Bi³⁺ doping expands the unit cell due to its larger ionic radius than La³⁺. Magnetically, all exhibit ferromagnetism and soft magnetic features, with magnetization decreasing as Bi content increases. The x = 0.2 and 0.5 samples show two distinct Curie temperatures, both decreasing with Bi doping, whereas the higher Curie temperature vanishes in the x = 1.0 sample, likely due to Bi-induced structural changes. Electrically, all display semiconducting behavior (resistivity: x = 0.5 > x = 0.2 > x = 1.0) and negative magnetoresistance at 200 K, peaking at 12% (x = 0.5) and 7.5% (x = 1.0). For the x = 1.0 sample, negative magnetoresistance strengthens with decreasing temperature (130–200 K), with MR-H curves showing herringbone and arc shapes.