Magnetically induced phonon splitting in ACr₂O₄ spinels from first principles

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We study the magnetically-induced phonon splitting in cubic ACr₂O₄ (A=Mg, Zn, Cd, Hg) spinels from first principles, and demonstrate that the sign of the splitting, which is experimentally observed to be opposite in CdCr₂O₄ compared to ZnCr₂O₄ and MgCr₂O₄, 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 that includes only the nearest neighbor exchange. Finally, 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.