Interrelation between domain structures and polarization switching in hybrid improper ferroelectric Ca3(Mn,Ti)2O7

Abstract

Ca3Mn2O7 and Ca3Ti2O7 have been proposed as the prototypical hybrid improper ferroelectrics (HIFs), and a significant magnetoelectric (ME) coupling in magnetic Ca3Mn2O7 is, in fact, reported theoretically and experimentally. Although the switchability of polarization is confirmed in Ca3Ti2O7 and other non-magnetic HIFs, there is no report of switchable polarization in the isostructural Ca3Mn2O7. We constructed the phase diagram of Ca3Mn2-xTixO7 through our systematic study of a series of single crystalline Ca3Mn2-xTixO7 (x = 0, 0.1, 1, 1.5, and 2). Using transmission electron microscopy, we have unveiled the unique domain structure of Ca3Mn2O7: the high-density 90° stacking of a- and b-domains along the c-axis due to the phase transition through an intermediate Acca phase and the in-plane irregular wavy ferroelastic twin domains. The interrelation between domain structures and physical properties is unprecedented: the stacking along the c-axis prevents the switching of polarization and causes the irregular in-plane ferroelastic domain pattern. In addition, we have determined the magnetic phase diagram and found complex magnetism of Ca3Mn2O7 with isotropic canted moments. These results lead to negligible observable ME coupling in Ca3Mn2O7 and guide us to explore multiferroics with large ME coupling.

Hybrid Improper Ferroelectricity in (Sr,Ca)3Sn2O7 and Beyond: Universal Relationship between Ferroelectric Transition Temperature and Tolerance Factor in n = 2 Ruddlesden–Popper Phases

“…The black circles show the data previously reported for Ca3 Ti 2 O 7 , 32 Sr 3 Zr 2 O 7,37 and Ca 3 Mn 2 O 7 40. The squares indicate the reported data for solidsolution systems, (Ca,Sr) 3 Ti 2 O 734 and Ca 3 (Ti,Mn) 2 O 7 32,35. function of t. T C is found to monotonically increase with decreasing t. Because of the ubiquity of t in characterizing perovskite units, we can extend the compositional range to other n = 2 RP ferroelectrics.…”

“…A non-distorted structure forms with t ~ 1.0, whereas for smaller t values (0.8 < t < 1.0), the A-site cation is too small for its site resulting in a low-symmetry structure with rotated and/or tilted BO 6 octahedra. Figure 10 plots the T C s of (Sr 1−x Ca x ) 3 Sn 2 O 7 (x = 0, 0.1, and 0.2) system as a 34 , and Ca 3 (Ti,Mn) 2 O 7 32,35 . In the suite of fifteen different A 3 B 2 O 7 ferroelectrics, T C s range from below room temperature (~ 280 K) to about 1100 K. We find a linear relationship between the T C and t (Figure 10).…”

“…This form of ferroelectricity should be prevalent in perovskiterelated materials because the octahedral rotations/tilts are ubiquitous structural distortions 21 (which are primarily of geometric origin and are driven by the size mismatch of the constituent ions). Indeed, a number of layered perovskites have been proposed as potential hybrid improper ferroelectrics through the integrated approach of symmetry arguments and first-principles calculations [22][23][24][25][26][27][28][29][30] , some of which have been experimentally confirmed to exhibit switchable polarization [31][32][33][34][35][36][37][38] , or at least crystalize in polar structures [39][40][41][42][43][44][45][46] . One can now utilize group theory to elucidate symmetry breaking caused by given distortions and identify whether their combinations result in a polar symmetry, and then the ferroelectricity.…”

Soft antiphase tilt of oxygen octahedra in the hybrid improper multiferroicCa3Mn1.9Ti0.1O7

“…A reasonable explanation is the weak SOI associated with the 3d Mn ion compared to 5d-electron iridates [39]. Although small, the unambiguous existence of the canted moment in conjunction with the soft oxygen octahedral tilt mode offers a feasible strategy to achieve magnetoelectricity control in this layered perovskite, i.e., switching the direction of net moment with electric field [18,40].…”

Direct Magnetization-Polarization Coupling in BaCuF4

“…The proof of concept has been shown theoretically by Benedek and Fennie in Ca 3 Mn 2 O 7 [2] where the coupling mechanism with magnetism relies on the improper origin of the polarization that indirectly couples with the magnetization. Unfortunately, the experimental efforts to verify this prediction have, so far, shown that the electric po-larization in Ca 3 Mn 2 O 7 cannot be switched which seems to indicate that this crystal might not be the best candidate for magnetization reversal through an electric field [6]. Following the same strategy, layered materials with formula A n B n X 3n+2 appeared to be other favorable candidates [7][8][9].…”