Emergence of a Multiferroic Half-Metallic Phase in ${\mathrm{Bi}}_{2}{\mathrm{FeCrO}}_{6}$ through Interplay of Hole Doping and Epitaxial Strain

Emergence of a Multiferroic Half-Metallic Phase in ${Bi}_{2} {FeCrO}_{6}$ through Interplay of Hole Doping and Epitaxial Strain

Paresh C. Rout and Varadharajan Srinivasan

Phys. Rev. Lett. 123, 107201 – Published 5 September 2019

Abstract

Epitaxial strain has been shown to drive structural phase transitions along with novel functionalities in perovskite-based thin films. Aliovalent doping at the $A$ site can drive an insulator-to-metal and magnetic transitions in perovskites along with a variety of interesting structural and electronic phenomena. Using first-principles calculations, we predict the formation of a multiferroic half-metallic phase with a large magnetic moment in the double perovskite, ${Bi}_{2} {FeCrO}_{6}$ , by coupling epitaxial strain with $A$ -site hole doping. We also demonstrate that epitaxial strain can be used to manipulate the hole states created by doping to induce half-metal to insulator, antipolar to polar, antiferromagnetic to ferromagnetic, orbital ordering and charge ordering transitions. Our work also suggests that hole doping under strain could lead to mitigation of issues related to antisite defects and lowered magnetization in thin films of the material.

Received 6 September 2018
Revised 17 July 2019

DOI:https://doi.org/10.1103/PhysRevLett.123.107201

Physics Subject Headings (PhySH)

Electronic structure Ferroelectricity Magnetism Phase transitions

Thin films

Density functional theory

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Paresh C. Rout¹ and Varadharajan Srinivasan ^1,2

¹Department of Physics, Indian Institute of Science Education and Research Bhopal, Bhopal 462 066, India
²Department of Chemistry, Indian Institute of Science Education and Research Bhopal, Bhopal 462 066, India

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Vol. 123, Iss. 10 — 6 September 2019

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Figure 1
Total energy difference (in eV per formula unit) as a function of epitaxial strain in the three lowest energy phases of ${BiSrFeCrO}_{6}$ : black circles represent the FM state of $D 0$ structure in $R 3$ phase, red diamonds, the FM state of $D 0$ structure in $P 2_{1} / n$ -phase, and blue asterisks, the $C$ -AFM state of $D 1$ structure in $R 3$ phase. The indigo triangles represent the FM state of $D 0$ structure in $R 3 (1)$ phase which occurs as a result of an IPT at 2% strain. The dotted vertical lines indicate the locations of the isosymmetric phase transition (IPT).
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Figure 2
(a) The average oxygen octahedral rotation (OOR) and oxygen octahedral tilt (OOT) angles as a function of biaxial strain for all the stable phases. The IPTs (indicated by vertical dotted lines) are characterized by sharp changes in the OOT and OOR in the antipolar ( $P 2_{1} / n$ ) phase at 0% strain and in the polar ( $R 3$ ) phase at $- 2 %$ and $+ 2 %$ strain; and (b) The Bi, Sr displacements (in Å), along the pseudocubic [110] direction, from their respective positions in the ideal perovskite structure: open black circles (as well as the dotted black line) represent Bi1 displacements, blue asterisks, Bi2 displacements, open red squares and green diamonds, Sr1 and Sr2 displacements, respectively, where 1 and 2 refer to the two planes of $A$ sites in the supercell. The vertical dashed lines separate the various phases identified in 1.
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Figure 3
Total and projected density of states (PDOS) of lowest energy phases of ${BiSrFeCrO}_{6}$ at various strains (top panel) and the spatial distribution of the corresponding hole states (bottom panel) on selected planes (indicated below the figures). (a) The antipolar ( $P 2_{1} / n$ ) $D 0$ phase at $- 4 %$ strain; (b) the polar ( $R 3$ ) $D 0$ phase at 0% strain, (c) the polar ( $R 3$ ) $D 1$ phase at $+ 2 %$ strain (Cr1 and Cr2 refer to the two spin inequivalent Cr atoms in the system); and (d) the isosymmetric polar ( $R 3 (1)$ ) $D 0$ phase at $+ 4 %$ .
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Figure 4
Epitaxial strain induced phase transitions in ${Bi}_{1.5} {Sr}_{0.5} {FeCrO}_{6}$ . (a) Evolution of total energy (in eV per formula unit) with epitaxial strain in the three lowest energy phases: black circles represent the FM state of $D 0$ $R 3$ structure, red squares, the FM state of $D 0$ structure $P 2_{1} / n$ structure, and blue diamonds, the $C$ -AFM state of $D 1$ structure $P 2_{1} / n$ structure. The energy of the $C$ -AFM state of $D 1$ structure in $R 3 (1)$ phase, which was stable at 50% doping, is also presented (indigo asterisks) for purposes of comparison. All the energies are positioned with respect to the energy of the $D 0$ FM (R3) state at 1% strain, (b) Total and projected density of states (PDOS) of the antipolar ( $P 2_{1} / n$ ) phase of $D 1$ structure at $- 4 %$ strain, and (c) The atomic charge difference between the two types of Cr atoms (Cr1 and Cr2) and magnetic moment per formula unit of $C$ -AFM $D 1$ structure as a function of compressive strain.
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Physical Review Letters

Emergence of a Multiferroic Half-Metallic Phase in Bi2FeCrO6 through Interplay of Hole Doping and Epitaxial Strain

Paresh C. Rout and Varadharajan Srinivasan

Phys. Rev. Lett. 123, 107201 – Published 5 September 2019

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Emergence of a Multiferroic Half-Metallic Phase in ${Bi}_{2} {FeCrO}_{6}$ through Interplay of Hole Doping and Epitaxial Strain