Relationship between crystal structure and multiferroic orders in orthorhombic perovskite manganites

Abstract

We use resonant and non-resonant X-ray diffraction measurements in combination with firstprinciples electronic structure calculations and Monte Carlo simulations to study the relationship between crystal structure and multiferroic orders in the orthorhombic perovskite manganites, o-RMnO3 (R is a rare-earth cation or Y). In particular, we focus on how the internal lattice parameters (Mn-O bond lengths and Mn-O-Mn bond angles) evolve under chemical pressure and epitaxial strain, and the effect of these structural variations on the microscopic exchange interactions and long-range magnetic order. We show that chemical pressure and epitaxial strain are accommodated differently by the crystal lattice of o-RMnO3, which is key for understanding the difference in magnetic properties between bulk samples and strained films. Finally, we discuss the effects of these differences in the magnetism on the electric polarization in o-RMnO3. * natalya.fedorova@mat.ethz.ch † nicola.spaldin@mat.ethz.ch 1 N. A. Spaldin and M. Fiebig, Science 309, 391 (2005).

Nanoengineering room temperature ferroelectricity into orthorhombic SmMnO3 films

“…This is mainly dominated by the decrease of a/b lattice parameters (d 110 strain −3.6%). Hence the Mn-O bond length will be decreased in line with the in-plane compression and this will modify the in-plane magnetic interactions of Mn moments and spin-order states 10,14,39 . On going from o-SMO1 to o-SMO2, since the a and b lattice parameters shrink but c expands, the Mn-O-Mn Fig.…”

“…Therefore, achieving multiferroicity requires a delicate balance of bond angle and bond length tuning. Such tuning has not been demonstrated to date, and hence there are no reports of RT ferroelectricity in o-RMnO 3 13,14 . The highest reported FE transition temperature (T C,FE ) in o-RMnO 3 films is below~75 K and the highest spin-driven FE polarisation is P~1.5 μC cm −2 under high pressure and high magnetic field 5,18 .…”

“…In terms of the magnetic properties, low-temperature ferromagnetism with magnetisation (M) values near~1µ B Mn −1 have been reported in thin o-RMnO 3 films 11,12 . Ferromagnetic (FM) ordering in o-RMnO 3 originates due to epitaxial strain which changes the balance between AFM and FM interactions 13,14 and breaks the long range AFM order at the boundary of different domains 5,15 . Spin-driven ferroelectricity with large FE polarisation is expected with large Mn-O-Mn bond angles and small Mn-O bond lengths 16 .…”

Strain-induced robust magnetic anisotropy and room temperature magnetoelectric coupling effect in epitaxial SmFeO3 film

“…In order to explain the origin of the magnetically induced ferroelectricity, a large number of theoretical models were proposed one after another, such as reverse Dzyaloshinskii-Moriya (D-M) interaction [12], spin-dependent p-d hybridization and exchange striction mechanism [13,14]. So far, numerous single-phase multiferroic materials have been found, such as (Y, Sr, Gd, Dy, Tb, Ho, Lu)MnO 3 films [15][16][17][18], (Dy, Gd, Tb, Ho, Er, Lu)CrO 3 films [19][20][21][22][23], (Gd, Dy, Yb)FeO 3 films [24][25][26], EuTiO 3 films [27], hexaferrite Ba 2−x Sr x Mg 2 Fe 12 O 22 single crystal [28], and LaFeO 3 polycrystal [29]. Despite rich characteristics and fascinating physics, the low working temperature and weak saturation magnetization (M s ) restrict the practical applications of these materials.…”

Lattice and spin dynamics in multiferroic BiFeO3 and RMnO3

“…However, for o - R MnO 3 , the above Hamiltonians cannot precisely describe the complex phase diagram of magnetic states, such as the existence of E-AFM states. The Ising mode [ 65 ], two-orbital double-exchange model [ 66 , 67 ], and bond alternation model of FM exchange [ 68 ] were proposed, before higher-order coupling terms such as a biquadratic term \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{upgreek} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} }{}${{\cal H}_{{\rm{biq}}}}$\end{document} [ 69 ] and four-spin ring exchange term \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{upgreek} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} }{}${{\cal H}_{4{\rm{sp}}}}$\end{document} [ 70 ] were included to predict magnetic structures and important features of spin-wave spectra that cannot be obtained from the Heisenberg Hamiltonian [ 71–73 ]: \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{upgreek} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} }{}\begin{equation*} {{\cal H}_{{\rm{biq}}}} = {\rm{\ }} - \mathop \sum \limits_{i,j} {B_{ij}}{( {{S_i} \cdot {S_j}} )^2} \end{equation*}\end{document} …”