Fe Substitution Modified Spontaneous Exchange Bias and Magnetic Properties Tunability of La ₂ Co _2‐x Fe _x O ₆ Nanoparticles

In this article, the effects of increasing the Fe concentration in La 2 Co 2‐x Fe x O 6 ( x = 1.10, 1.15, 1.20, 1.25, and 1.30) nanoparticles were systematically investigated. The Rietveld refinement analysis of La 2 Co 2‐x Fe x O 6 compositions confirmed the orthorhombic structure. A clear increase in the lattice parameters and unit cell volume was observed, accompanied by enhanced distortion of the FeO2Co bond angle with increasing Fe content. Room‐temperature magnetic hysteresis indicates weak ferromagnetic behavior, with both coercivity and remanent magnetization increasing as the Fe content increases. The Nèel temperature of La 2 CoFeO 6 (∼270 K [1]) was tuned toward higher temperatures with small increments in the Fe concentration. For composition, x = 1.10, a magnetic transition near ∼300 K was observed, along with a large exchange bias (EB) effect at 2 K under zero‐field cooling conditions. The magnitude of the EB progressively decreases as Fe concentration increases toward the end‐member LaFeO 3 , which is known to be an antiferromagnetic insulator. This reduction is due to decreasing competition between the antiferromagnetic and ferromagnetic interactions caused by increased homogeneity in the oxidation states of the Fe/Co B‐site ions, as confirmed by X‐ray photoelectron spectroscopy studies. The observed near‐room‐temperature magnetic transition and significant EB suggest the promising potential of these materials for spintronic applications.