Large ferroelectric polarization in the new double perovskite NaLaMnWO6 induced by non-polar instabilities

Abstract

Based on density functional theory calculations and group theoretical analysis, we have studied NaLaMnWO6 compound which has been recently synthesized [Phys. Rev. B 79, 224428 (2009)] and belongs to the AA ′ BB ′ O6 family of double perovskites. At low temperature, the structure has monoclinic P 21 symmetry, with layered ordering of the Na and La ions and rocksalt ordering of Mn and W ions. The Mn atoms show an antiferromagnetic (AFM) collinear spin ordering, and the compound has been reported as a potential multiferroic. By comparing the low symmetry structure with a parent phase of P 4/nmm symmetry, two distortion modes are found dominant. They correspond to MnO6 and WO6 octahedron tilt modes, often found in many simple perovskites. While in the latter these common tilting instabilities yield non-polar phases, in NaLaMnWO6 the additional presence of the A-A ′ cation ordering is sufficient to make these rigid unit modes as a source of the ferroelectricity. Through a trilinear coupling with the two unstable tilting modes, a significant polar distortion is induced, although the system has no intrinsic polar instability. The calculated electric polarization resulting from this polar distortion is as large as ∼ 16 µC/cm 2 . Despite its secondary character, this polarization is coupled with the dominant tilting modes and its switching is bound to produce the switching of one of two tilts, enhancing in this way a possible interaction with the magnetic ordering. The transformation of common non-polar purely steric instabilities into sources of ferroelectricity through a controlled modification of the parent structure, as done here by the cation ordering, is a phenomenon to be further explored.Perovskite oxides are one of the most interesting and studied classes of inorganic compounds. They show many interesting properties such as ferroelectricity, ferromagnetism, superconductivity, colossal magnetoresistance, etc.[1] The prototype structure is the simple ABO 3 , where the three-dimensional framework of corner-sharing BO 6 octahedra form 12-coordinate cavities occupied by the larger A cations. The possibility of A-or B-substitution gives rise to a large compositional range with different properties and symmetries. A well studied case is the 50:50 substitution of B-site in the double perovskites A 2 BB ′ O 6 , where the B and B ′ cations order in a rock-salt fashion.[2, 3] Analogously, ordering of the A-cations can also occur, showing a strong preference for a layered arrangement.[4-6] Finally, simultaneous Aand B-site cation ordering can also occur in compounds of type AA ′ BB ′ O 6 .[7] These compounds are interesting from a structural point of view since they exhibit rocksalt ordering of B-site cations and layered ordering of A-site cations. However, they are relatively unexplored, * Present address: Graduate School of Engineering Science, Osaka University, 1-3 Machikaneyama, Toyonaka, Osaka 560-8531, Japan because this type of ordering is very rare. [7,8] Clearly, the presence of four different distinct cation sit...

First-principles study of ferroelectricity induced by p–d hybridization in ferrimagnetic NiFe 2 O 4

“…This indicates the P 4 1 22 NFO to be improper multiferroics (with the ferrimagnetic order as discussed below). When comparing with the conventional improper multiferroics, the calculated polarization is remarkably large, but not very surprising as compared to other recently found spinel ferrites like Fe 3 O 4 , LuFe 2 O 4 and NaLaMnWO 6 [20,23,26,29]. We note that the polarization comes from spin down elec- trons for the case of duu spin configuration, while for the case of udd spin configuration (another lowest-energy spin configuration with the opposite magnetic moment to the duu configuration) it is from spin up electrons.…”

“…In these ferrites, moreover, the charge and spin degrees of freedom of electrons can be controlled simultaneously, because they have ferrimagnetic order and thus may have non-zero magnetization. Recently, two primary non-polar distortions like tilting and rotation of oxygen octahedra driven by electronic factors (i.e., Jahn-Teller effects) were found to induce the breaking of inversion symmetry and produce a large ferroelectric polarization in the new class of double perovskites AA ′ BB ′ O 6 ; SrTiO 3 /PbTiO 3 superlattice [28], NaLaMnWO 6 [9,29] with a very large polarization of about 16 µC/cm 2 , and Ca 3 Mn 2 O 7 [10] are typical compounds belonged to this materials class. These materials have weak ferromagnetism and thus a significant ME coupling is expected.…”

Turning ABO3 Antiferroelectrics into Ferroelectrics: Design Rules for Practical Rotation‐Driven Ferroelectricity in Double Perovskites and A3B2O7 Ruddlesden‐Popper Compounds

“…Another way of stating the challenge is, "how can octahedral rotations induce a spontaneous polarization?" By themselves octahedral rotations cannot induce ferroelectricity in simple perovskites, but recent work has demonstrated that they can induce ferroelectricity in layered A-site ordered double perovskites and superlatties 6,[13][14][15][16] and in Ruddlesden-Popper phases 17,18 (and other layered perovskites [19][20][21] ). The most common realization of this novel rotation-centric, ferroelectric mechanism has been referred to as hybrid improper ferroelectricity (HIF) 18 .…”

Electric Field Control of Jahn-Teller Distortions in Bulk Perovskites

“…This concept is related to an unusual coupling of lattice modes, giving rise in the free energy expansion to a trilinear term −λPR 1 R 2 linking the polar motion P to two independent nonpolar distortions R 1 and R 2 . Such a coupling was identified in various layered perovskites [8,9,[12][13][14][15], metal-organic framework [16,17], and can even appear in bulk ABO 3 perovskites [18,19]. Interestingly, in Ruddlesden-Popper compounds [9,20] and ABO 3 =A 0 BO 3 superlattices [21], this trilinear coupling appeared as a practical way to achieve electric control of nonpolar antiferrodistortive (AFD) motions associated with the rotation of the oxygen octahedra (i.e., monitoring P with an electric field will directly and sizeably tune the nonpolar modes R 1 and/or R 2 ).…”