Magnetic Properties of the Composite Formed from LaSr(CoFe)\(_{1/2}\)O\(_{4}\) Ruddlesden-Popper Phase and (LaSr)\(_{1/2}\)(CoFe)\(_{1/2}\)O\(_3\) Perovskite

Abstract

A composite material composed of 79% LaSr(CoFe)\(_{1/2}\)O\(_4\) Ruddlesden-Popper phase and 21% (LaSr)\(_{1/2}\) (CoFe)\(_{1/2}\)O\(_3\) perovskite was studied to explore its magnetic properties. In a low magnetic field of \(100 \, \text {Oe}\), the material exhibits superparamagnetic behavior with a blocking temperature of \(T_B = 133 \, \text {K}\). In contrast, at a high field of 10 000 Oe, the susceptibility deviates from paramagnetic behavior below 250 K, showing a gradual increase dominated by the perovskite phase. Below 50 K, the magnetization could be described as a combination of paramagnetic, superparamagnetic, and ferromagnetic contributions, with the saturation magnetization decreasing as the temperature dropped, driven by the perovskite phase. Mössbauer spectroscopy identified three groups of iron species: Fe\(^{4+}\) in the perovskite phase, suggesting a Fe\(^{4+}\)/Co\(^{3+}\) mixture rather than a 50:50 mixture of Co\(^{3+}\)/Fe\(^{3+}\) and Co\(^{4+}\)/Fe\(^{4+}\). The other two groups, Fe\(^{3+\delta _1}\) and Fe\(^{3-\delta _2}\), were associated with the Ruddlesden-Popper phase, where Fe\(^{3+\delta _1}\) plays a crucial role in stabilizing the crystal structure by compensating for the differences in ionic radii between Fe\(^{3+}\) and Co\(^{3+}\).