This book explores magnetic properties and critical temperatures in inverse ferrite Fe₃⁺(M₂⁺Fe₃⁺)O₄ spinels (e.g., Fe, Co, Ni). It calculates transition and Curie Weiss temperatures, providing insights into their thermodynamic behavior. Using the full potential linearized augmented plane wave (FP-LAPW) method, it investigates electrical and magnetic structures of spinel chromite, revealing magnetic moments in MnCr₂S₄. Seebeck coefficient and electrical conductivity are also calculated. Advanced techniques like Monte Carlo, DFT+U, and FLAPW analyze magnetic characteristics of LiMn₁.₅Ni₀.₅O₄ and electronic/magnetic structures of Fe₃O₄. High-temperature series expansions calculate Néel temperature and critical exponents, while GFT determines thermal magnetization and susceptibility. The analysis exposes exchange interactions' effects on magnetic order and introduces asymmetric phases in ferrimagnetic spinel systems. This book serves as an invaluable resource for researchers, academics, and enthusiasts seeking a comprehensive understanding of magnetic properties and critical phenomena within diverse spinel materials.