Multiferroic crossover in perovskite oxides

Abstract

Recently, the perovskite BiCoO${}_3$ has been shown experimentally to be isostructural with PbTiO${}_3$, while simultaneously the $d^6$ Co${}^{3+}$ ion has a high spin ground state with $C$-type antiferromagnetic ordering. Using hybrid density functional calculations, we investigate the atomic, electronic and magnetic structure of BiCoO${}_3$ to elucidate the origin of the multiferroic state. To begin with, we perform a qualitative trend sudy of the role of $d$ electrons in affecting the tendency for perovskite materials to exhibit a ferroelectric distortion; this work initially explores a qualitative trend study in artificial cubic and tetragonal LaBO${}_3$ perovskites. We choose La as the A-cation so as to remove the effects of Bi $6s$ hybridization. Through first-principles calculations of the LaBO${}_3$ series, where B is a $d^0-d^8$ cation from the $3d$-block, the trend study reveals that increasing the $d$ orbital occupation initially removes the tendency for a polar distortion, as expected. However, for high spin $d^5-d^7$ and $d^8$ cations a strong ferroelectric instability is recovered. We explained this effect in terms of the pseudo Jahn-Teller theory for ferroelectricity. It is shown that, in some cases, unpaired electron spins actually drive ferroelectricity, rather than inhibit it, which represents a shift in the understanding of how ferroelectricity and magnetism interact in perovskite oxides. It follows, that for the case of BiCoO${}_3$, the Co${}^{3+}$ ion plays a major role in the ferroelectric lattice instability. Importantly, the ferroelectric polarization is greatly enhanced when the Co${}^{3+}$ ion is in the high spin state, when compared to the nonmagnetic, low spin state, and a large coupling of the electrical and magnetic polarization is present. Importantly, it is demonstrated that the ground spin state is switched by reducing the internal ferroelectric polarization.

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• Engineering multiferroism in CaMnO${}_3$
• Non-$d^0$ Mn-driven ferroelectricity in antiferromagnetic BaMnO${}_3$
• Spin-phonon coupling effects in transition-metal perovskites:a DFT+$U$ and hybrid-functional study
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Cited by in corpus (4)

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• Origin and tuning of room-temperature multiferroicity in Fe doped BaTiO${}_3$
• Electronic structure of pristine and Ni-substituted LaFeO${}_3$ from near edge x-ray absorption fine structure experiments and first-principles simulations
• Double Perovskite Structure Induced by Co Addition to PbTiO${}_3$ : Insights from DFT and Experimental Solid State NMR Spectroscopy