Strong Spin‐Lattice Coupling Through Oxygen Octahedral Rotation in Divalent Europium Perovskites

First‐principles calculations reveal that in divalent europium perovskites Eu M O 3 ( M = Ti, Zr, and Hf), antiferromagnetic superexchange interactions via n d states of the B‐site M cations ( n = 3, 4, and 5, respectively) are enhanced by rotations of the M O 6 octahedra. The octahedral rotations involved in a structural change from cubic $ Pm{\bar 3}m $ to orthorhombic Pbnm structures not only reduce energy gaps between the Eu 4f and M n d bands but also point the M n d orbitals at the Eu sites, leading to a significant overlap between the M n d and Eu 4f orbitals. These results reveal that the octahedral rotations are indispensable for antiferromagnetic ordering observed for EuZrO 3 and EuHfO 3 , and put these perovskites into a class of materials exhibiting a novel type of strong coupling between their magnetism and octahedral rotations.