Magnetically induced phonon splitting inACr2O4spinels from first principles

We study the magnetically-induced phonon splitting in cubic $A{\mathrm{Cr}}₂{\mathrm{O}}₄$ ($A=\text{Mg}$, Zn, Cd) spinels from first principles and demonstrate that the sign of the splitting, which is experimentally observed to be opposite in ${\mathrm{CdCr}}₂{\mathrm{O}}₄$ compared to ${\mathrm{ZnCr}}₂{\mathrm{O}}₄$ and ${\mathrm{MgCr}}₂{\mathrm{O}}₄$, is determined solely by the particular magnetic ordering pattern observed in these compounds. We further show that this interaction between magnetism and phonon frequencies can be fully described by the previously proposed spin-phonon coupling model [C. J. Fennie and K. M. Rabe, Phys. Rev. Lett. 96, 205505 (2006)] that includes only the nearest neighbor exchange. Using this model with materials specific parameters calculated from first principles, we provide additional insights into the physics of spin-phonon coupling in this intriguing family of compounds.