E -type noncollinear magnetic ordering in multiferroic o−LuMnO3

Abstract

Multiferroic orthorhombic o-LuMnO 3 exhibits large ferroelectric polarization induced by an E-type magnetic order. Recently, the E-type magnetic phase in LuMnO 3 was proposed to feature magnetic moments tilted away from the collinear ordering. We employed neutron diffraction to determine the symmetry of the magnetic order in o-LuMnO 3. We observed that below T N = 39 K, the Mn 3+ spins order into an incommensurate amplitudemodulated phase that obeys the Pbnm crystal symmetry and is paraelectric. The incommensurate phase locks into a commensurate phase at T C = 35.5 K described by a fully antiferromagnetic and noncollinear E-type order. This noncollinear E-type ordering breaks the spatial inversion symmetry and induces a spontaneous polarization at T C. At T = 2 K, an appreciably large electric polarization was observed similar to that of other orthorhombic manganites featuring E-type magnetic order. We also present a Pbnm symmetry-allowed Dzyaloshinskii-Moriya interaction that explains the noncollinear E-type order in the commensurate phase. These results are in qualitative agreement with the type of distortions from collinear E-type antiferromagnetic order found using Monte Carlo simulation for rare-earth manganites [M.

Unique coexistence of incommensurate and commensurate magnetic order in TbMnO3 strained films

“…We want to point out that the large P values ∼1 μC/cm 2 at T = 37.5 K) observed in thin strained TbMnO 3 films originate from a combined effect of symmetric (S • S)-type exchange striction for E-type CM order and an antisymmetric (S × S)-type Dzyaloshinskii-Moriya interaction of the abspiral ICM order. Similar contributions to the FE polarization are observed in bulk Eu 1−x Y x MnO 3 and Y 1−y Lu y MnO 3 [11].…”

“…Since the (0 1 0) reflection is forbidden for an orthorhombic symmetry, the existence of the (0 1 0) reflection in orthorhombic YMnO 3 was taken as evidence for the magnetic E-type order. A symmetry analysis for o − RMnO 3 confirmed that the existence of a forbidden nonmagnetic structural reflection implies purely a breaking of the rotational symmetry element along the b axis (2 b ) [11]. This symmetry argument is supported by the simultaneous appearance of ferroelectric ordering and the (0 1 0) reflection.…”

Multiferroic phase diagram of E -type RMnO3 films studied by neutron and x-ray diffraction

“…Neutron diffraction gives access to a large Ewald sphere and enables us to measure the intensity of Q = (0 q 1) reflection for the family of strained o-RMnO 3 (R = Gd-Lu) thin films. Magnetic structure factor calculations indicate that the (0 q 1) reflection is one of the strongest magnetic reflections of the observed ground state in o-RMnO 3 , such as a spiral or an E-type phase [4,27]. The measured intensity of the magnetic reflections is sensitive to the projection of the magnetization components normal to Q.…”

“…[25], all films show a compressive strain along the a axis while the strain along the c axis varies with the radius of the R ions. The films are compressively strained along c for R = Gd-Dy, and have a tensile strain for [34,56,57], TbMnO 3 [4,34], DyMnO 3 [34,58], HoMnO 3 [26,34], ErMnO 3 [29], TmMno 3 [39], YbMnO 3 [28,38], LuMnO 3 [27], and T FE of RMnO 3 films [24,25], and T N of TbMnO 3 film [24].…”

“…Our results are in agreement with the proposed change of the multiferroic mechanism due to strain [24,25] which was shown to stabilize the E-type order and induce a large FE polarization along the a axis. The onset of the FE order occurs in the ICM phase independent of the E-type ordering, unlike in bulk o-RMnO 3 (R = Ho-Lu) [26][27][28][29]. We also address the role of the 4f rare-earth and 3d Mn magnetic order interplay.…”