Louis Néel's 1948 paper explores the magnetic properties of ferrites, focusing on ferrimagnetism and antiferromagnetism. He analyzes substances composed of magnetic ions distributed on two crystallographically distinct sites, A and B. By generalizing the molecular field approximation, he characterizes magnetic interactions using three molecular field coefficients. In some cases, substances exhibit ferrimagnetic properties, characterized by a lower saturation magnetization than ordinary ferromagnets, a different temperature dependence of spontaneous magnetization, and a hyperbolic temperature dependence of the inverse susceptibility above the Curie point. When the ions are equally distributed between sites A and B, the theory aligns with previous antiferromagnetic studies. Néel also discusses a case between ferro- and ferrimagnetism, and shows how the theory explains the paramagnetic and ferromagnetic properties of ferrites. He calculates key parameters for copper ferrites, confirming the distribution of ferric ions on two distinct sites, consistent with earlier ideas. The paper also addresses the anomalous properties of zinc and cadmium ferrites. Néel's theory is applied to experimental data, allowing the calculation of molecular field coefficients for ferrites and antiferromagnets. He highlights the importance of long-range interactions between atoms, mediated by anions, and the role of superexchange mechanisms. The paper concludes with a detailed analysis of the temperature dependence of magnetization and susceptibility, showing how the theory explains experimental results for various ferrite and antiferromagnetic materials.Louis Néel's 1948 paper explores the magnetic properties of ferrites, focusing on ferrimagnetism and antiferromagnetism. He analyzes substances composed of magnetic ions distributed on two crystallographically distinct sites, A and B. By generalizing the molecular field approximation, he characterizes magnetic interactions using three molecular field coefficients. In some cases, substances exhibit ferrimagnetic properties, characterized by a lower saturation magnetization than ordinary ferromagnets, a different temperature dependence of spontaneous magnetization, and a hyperbolic temperature dependence of the inverse susceptibility above the Curie point. When the ions are equally distributed between sites A and B, the theory aligns with previous antiferromagnetic studies. Néel also discusses a case between ferro- and ferrimagnetism, and shows how the theory explains the paramagnetic and ferromagnetic properties of ferrites. He calculates key parameters for copper ferrites, confirming the distribution of ferric ions on two distinct sites, consistent with earlier ideas. The paper also addresses the anomalous properties of zinc and cadmium ferrites. Néel's theory is applied to experimental data, allowing the calculation of molecular field coefficients for ferrites and antiferromagnets. He highlights the importance of long-range interactions between atoms, mediated by anions, and the role of superexchange mechanisms. The paper concludes with a detailed analysis of the temperature dependence of magnetization and susceptibility, showing how the theory explains experimental results for various ferrite and antiferromagnetic materials.