Pressure-induced magnetic moment collapse and insulator-to-semimetal transition in BiCoO₃

Abstract

The structural stability, magnetic properties and electronic structure of tetragonal BiCoO(3) under pressure have been studied by first-principles density functional calculations. The calculated results reveal that no tetragonal-to-cubic and ferroelectric-to-paraelectric phase transitions occur up to 30 GPa with a volume compression of about 25%. An electronic spin crossover transition of the Co(3+) ion from the high-spin to nonmagnetic low-spin configuration (magnetic moment collapse) occurs at 4 GPa by about 4.87% volume compression, which is concomitant with a first-order isosymmetric transition and an insulator-to-semimetal transition. The metallization in BiCoO(3) is driven by the spin-state transition at high pressure. Coexistence of the structural, spin-state and insulator-to-semimetal transitions implies that there is a strong coupling among the lattice, spin and charge degrees of freedom in BiCoO(3).

Ab initiostudy of the giant ferroelectric distortion and pressure-induced spin-state transition in BiCoO3

“…Plain GGA [or local-spin-density approximation (LSDA)] calculations 5,6,11,13 seem to qualitatively re- produce the C-type AF and insulating ground state of BiCoO 3 in the ambient phase, which was ascribed to the strong Hund-exchange stabilized HS state of the Co 3+ ions (and thus the AF order and narrow bands) and to the well split-off xy-singlet orbital. However, the band gap of 0.6 eV and the Co 3+ spin moment of 2.4 µ B given by the GGA/LSDA calculations are much smaller than the experimental values of 1.7 eV and 3.2 µ B .…”

High pressure and multiferroics materials: a happy marriage

“…Oka et al (2010) investigated the HP behavior of BiCoO 3 by synchrotron and neutron powder diffraction and X-ray emission spectroscopy. A first-order tetragonal, PbTiO 3 -type, to orthorhombic, GdFeO 3 -type, phase transition has been observed at P = 3 GPa, in contrast to the proposed isostructural tetragonal to tetragonal transition by Ming et al (2009). The transition is accompanied by a HS to LS transition with an intermediate spin state present at the transition as determined from XES data.…”

“…Cobaltite perovskites, ACoO 3 . Ming et al (2009) studied the structural stability, and the magnetic and electronic properties of BiCoO 3 by first-principles calculations up to 30 GPa. The calculations reproduce the C-type antiferromagnetic structure as a ground state.…”

Determination of transition metal ion distribution in cubic spinel Co1.5Fe1.5O4 using anomalous x-ray diffraction

“…1,2 In various spinel systems, crystallographic coordination, charge/spin states and composition of transition metals play decisive role in structural 3,4 as well as magnetic properties. 4,5 Some interesting phenomena like charge transfer between metals and ligands under hydrostatic pressure, 6 high spin -low spin transition of transition metals under external perturbation, 7 chemical pressure leading to itinerant electron limit 4,8 etc., have been reported in these systems. Transition metals in nature occur in different oxidation (charge) states which usually have different magnetic moments depending on whether it is high-spin (HS), intermediate-spin (IS) or low spin (LS) state.…”