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

Abstract

First-principles calculations reveal that in divalent europium perovskitesEu 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 Pm3m 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 signifi cant 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.

Crystal structure and magnetic properties of EuZrO 3 solid solutions

“…32 The sequence of phases in the Ba x Eu 1− x ZrO 3 series at room temperature and the accompanying crystal symmetry can be deduced as follows (Table 1): 0 ≤ x ≤ 0.3, orthorhombic Pbnm ( a − a − c + ); 0.4 ≤ x ≤ 0.6, orthorhombic Ibmm ( a − a − c 0 ); x = 0.7, tetragonal I4/mcm ( a 0 a 0 c − ); and 0.80 ≤ x ≤ 1, cubic Pm 3̄ m ( a 0 a 0 a 0 ). 28 These deductions agree with the results given by Howard and Stokes for structural transition of ABO 3 perovskites. All of the fitted patterns are given in Fig.…”

“…[25][26][27] Furthermore, it was suggested by the hybrid Hartree-Fock density functional calculations that the lattice volume-expanded EuMO 3 prefers the FM interaction through the Eu 5d states to the AFM one via the M nd states, as a consequence of the reduced hybridization of the Eu 4f and M nd orbitals. 28 The volume expansions induced by the lattice mismatch between ETO thin films and different substrates can change the magnetic ground state of ETO from AFM to FM, experimentally supporting the theoretical calculations. 29 Based on the critical balance between AFM superexchange interaction via the M nd orbitals and FM indirect exchange interaction via Eu 5d states, the FM state resulting from the modification of crystal structure of EuMO 3 by engineering techniques was confirmed by the works mentioned above.…”

Unusual magnetic structure of the high-pressure synthesized perovskites ACrO3 (A=Sc , In, Tl)

“…On the other hand, the ground state of LuCrO 3 is G-type AFM structure when U is small, which also agrees with the documented experimental data [15], but the energy becomes closer to that of C-type AFM configuration as increases U. To understand the origin of the difference in these magnetic ground states, the exchange constants were estimated by mapping the total energy differences between the four magnetic configurations onto the Heisenberg Hamiltonian H = −2Σ i> j J i j S i • S j [41,42], where J i j is the exchange constant of magnetic interactions between Cr 3d spins at the i and j sites (see Fig. 1) and S i , S j are the spin vectors at these sites.…”

Magnetic and transport properties of EuTiO3thin films doped with Nb

“…Although the stable phase of EuTiO 3 is AFM, it has been shown experimentally and theoretically that introducing strain or volume expansion over a critical value leads to the stabilization of the FM phase. [11][12][13][14][15][16][17][18] In comparison with the theoretical reports, 17,18) the volume expansions for the present thin films lie in the regime where the AFM state is stabilized in terms of the lattice volumes. Therefore, we assume that the volume expansion in the present films have only minor effects on the magnetic properties.…”