Antiferromagnetism, superparamagnetism, and effects of A-cation distribution on magnetic properties of LaSrFeO4 Ruddlesden–Popper oxides: A combined experimental and theoretical study

Understanding the structure–property relationship in complex magnetic oxides is crucial for developing new magnetic materials. In this study, we synthesized LaSrFeO${}_4$ Ruddlesden–Popper oxide using spray-pyrolysis method. Electron paramagnetic resonance (EPR) spectra revealed two Fe-associated lines: a broad line indicating short-range antiferromagnetic (AFM) order, disappearing at 375 K, and a narrow line due to the presence of superparamagnetic phase. The magnetic moment from the linewidth’s temperature dependence was $10^{-19}$ A m². EPR intensity analysis estimated the superparamagnetic to antiferromagnetic phase ratio at 0.014 $\pm$ 0.004.

Using density-functional theory with Agapito–Curtarolo–Buongiorno–Nardelli (ACBN0) pseudo-hybrid functional including self-consistent Hubbard $U$ correction, we calculated the density of states for two La/Sr atomic distributions. The calculations show that a uniform La/Sr distribution perturbs 2D symmetry of Fe 3$d$ states, which can contribute to the observed lowering of the critical exponent $\beta$ for the magnetically ordered phase. These results highlight the impact of La/Sr distribution on LaSrFeO${}_4$’s properties.