First-principles stabilization of an unconventional collinear magnetic ordering in distorted manganites

Abstract

First-principles calculations have been performed for different collinear magnetic orderings in orthorhombic manganites, such as HoMnO 3 , TbMnO 3 , and YMnO 3 , showing large GdFeO 3 -like distortions. Our results suggest that the AFM-E type ordering, experimentally observed in HoMnO 3 and recently proposed from model Hamiltonian studies, is indeed the magnetic ground state. Its stability is strongly connected with octahedral distortions and points to the relevance of structural more than chemical effects. The calculated exchange constants, extracted from a Heisenberg model used to fit the first-principles total energies, show that the ferromagnetic in-plane nearest-neighbor coupling is reduced compared to less-distorted manganites, such as LaMnO 3 . In parallel, the antiferromagnetic next-nearest-neighbor coupling along planar Mn-O-O-Mn paths in highly distorted manganites plays a relevant role in the stabilization of the AFM-E spin configuration. In agreement with experiments, the density of states shows that this phase is insulating with an indirect band gap of ϳ0.5 eV.

The ferroelectric polarization of Y2CoMnO6aligns along the b-axis: the first-principles calculations

“…Earlier calculations did reveal that a varying Ueff influences the magnetic ground state of multiferroics, such as YMnO3 compound and CCMO. 37,38 Because the E*-AFM order is the experimentally determined ground state, one may focus on the range of Ueff from 1.0 eV to 2.0 eV. This choice is reasonable.…”

“…35 Even though in principle the DFT calculation can only deal with the zero-temperature ground state, it remains useful to understand the physics of materials, including those type-II multiferroics. [16][17][18][36][37][38][39] In this work, we pay attention to the full-scale first-principles calculations of the lattice and electronic structures of YCMO not only for checking the above prediction.…”

“…Similar larger calculated values were also reported in a few materials with exchange striction induced ferroelectricity, such as HoMnO3, YMnO3, and CCMO. [16][17][18]38 Besides the polycrystalline state of the samples, other possible reasons for this difference include the phase separated state and possible antisite occupations of Mn and Co ions in the samples. 28,29 The effects of antisite disorder on the magnetic properties of double perovskites Y2CoMnO6 have been experimentally investigated.…”

Strong coupling between the spin polarization of Mn and Tb in multiferroicTbMnO3determined by x-ray resonance exchange scattering

“…The model explicitly suppresses the ordering of the Tb 4f states. 21 The atomiclike 3d states lead to narrow peaks below ͑above͒ the Fermi energy in the majority ͑minority͒ band. The partial Mn 4p and the Tb 5d densities of states have maxima at the same energy.…”

Influence of magnetic order on phonon spectra of multiferroic orthorhombic YMnO3

“…The phase transition from the paraelectric Pnma structure to the ferroelectric P2 1 nm one results in the breaking of inversion symmetry and a rise of the macroscopic polarization along the a-axes [5,6]. To study these phase transitions and determine their microscopic mechanisms, the temperature dependencies of structural parameters, magnetization, IR and Raman spectra and other properties of orthorhombic YMnO 3 have been measured [5,6]. Among different features, the appearance of a spectral peak of 620 cm −1 at temperatures less than T FE has been observed.…”