Competing Magnetic Interactions and Magnetoelastic Coupling in Mn₃A (A = Ge, Sb) L₁₂ Compounds

We present first-principles studies of the structural, electronic, and magnetic properties of the cubic L1₂ compounds Mn₃Ge and Mn₃Sb. Finite-temperature magnetic behavior and magnetoelastic interactions are investigated using a supercell approach with special quasi-random spin configurations combined with the disordered local moment method. Our calculations reveal strong coupling between magnetic and lattice degrees of freedom in both systems. We also find that the exchange interactions are predominantly antiferromagnetic in the ferromagnetically ordered state but become ferromagnetic in the paramagnetic state. This behavior reflects a complex interplay among thermal spin disorder, electronic structure, and lattice relaxation, and implies the possibility of a significant magnetocaloric response. We further examine the effects of alloying and chemical disorder, suggesting routes to tune magnetoelastic and magnetocaloric performance in these Mn-based intermetallics.