N. Aliouane

Field-Induced Linear Magnetoelastic Coupling in Multiferroic TbMnO3

We have used in-field neutron and x-ray single-crystal diffraction to measure the incommensurability {delta} of the crystal and magnetic structures of multiferroic TbMnO{sub 3}. We show that the flop in the electric polarization at the critical field HC, for field H along the a and b axes, coincides with a first-order transition to a commensurate phase with propagation vector {kappa}=(0,1/4,0). In-field x-ray diffraction measurements show that the quadratic magnetoelastic coupling breaks down with applied field as shown by the observation of the first harmonic lattice reflections above and below HC. This indicates that magnetic field induces a linear magnetoelastic coupling.

Commensurate Dy magnetic ordering associated with incommensurate lattice distortion in multiferroic DyMnO{sub 3}

Synchrotron x-ray diffraction and resonant magnetic scattering experiments on a single crystal of orthorhombic DyMnO{sub 3} have been carried out between 4 and 40 K. Below T{sub N}{sup Dy}=5 K, the Dy magnetic moments order in a commensurate structure with propagation vector 0.5 b{sup *}. Simultaneous with the Dy magnetic ordering, an incommensurate lattice modulation with propagation vector 0.905 b{sup *} evolves while the original Mn induced modulation is suppressed and shifts from 0.78 b{sup *} to 0.81 b{sup *}. This points to a strong interference of Mn and Dy induced structural distortions in DyMnO{sub 3} besides a magnetic coupling between the Mn and Dy magnetic moments.

Magnetoelectric domain control in multiferroic TbMnO3

Visualizing ferroelectric domains Multiferroic materials support intertwined ferromagnetic and ferroelectric orders, with the magnetic field capable of controlling the electric order and vice versa. Matsubara et al. used second harmonic generation microscopy to visualize what happens to the ferroelectric domains in the multiferroic TbMnO3 when an externally applied magnetic field changes the direction of electric polarization by 90°. Unexpectedly, the domain walls, initially parallel to the polarization vector, did not change their shape or position. The resulting transition from neutral to charged domain walls may help in the development of future ferroelectric devices. Science, this issue p. 1112 Second harmonic generation microscopy visualizes the evolution of ferroelectric domains under an external magnetic field. The manipulation of domains by external fields in ferroic materials is of major interest for applications. In multiferroics with strongly coupled magnetic and electric order, however, the magnetoelectric coupling on the level of the domains is largely unexplored. We investigated the field-induced domain dynamics of TbMnO3 in the multiferroic ground state and across a first-order spin-flop transition. In spite of the discontinuous nature of this transition, the reorientation of the order parameters is deterministic and preserves the multiferroic domain pattern. Landau-Lifshitz-Gilbert simulations reveal that this behavior is intrinsic. Such magnetoelectric correlations in spin-driven ferroelectrics may lead to domain wall–based nanoelectronics devices.

New features in the phase diagram of TbMnO3

The (H,T)-phase diagram of the multiferroic perovskite TbMnO3 was studied by high-resolution thermal expansion α(T) and magnetostriction ΔL(H)/L measurements. Below TN 42 K, TbMnO3 shows antiferromagnetic order, which changes at TFE 28 K where simultaneously a spontaneous polarization P∥c develops. Sufficiently high-magnetic fields applied along a or b induce a polarization flop to P∥a. We find that all of these transitions are strongly coupled to the lattice parameters. Thus, our data allow for a precise determination of the phase boundaries and also yield information about their uniaxial pressure dependencies. The strongly hysteretic phase boundary to the ferroelectric phase with P∥a is derived in detail. Contrary to previous reports, we find that even in high-magnetic fields there are no direct transitions from this phase to the paraelectric phase. We also determine the various phase boundaries in the low-temperature region related to complex reordering transitions of the Tb moments.

Incompatible Magnetic Order in Multiferroic Hexagonal DyMnO3

Magnetic order of the manganese and rare-earth lattices according to different symmetry representations is observed in multiferroic hexagonal (h-)

Ga substitution as an effective variation of Mn-Tb coupling in multiferroic TbMnO 3

{\text{DyMnO}}_{3}

Field dependence of magnetic correlations through the polarization flop transition in multiferroic TbMnO 3 : Evidence for a magnetic memory effect

by optical second-harmonic generation and neutron diffraction. The incompatibility reveals that the

Anomalous thermal expansion and strong damping of the thermal conductivity of NdMnO3 and TbMnO3 due to 4f crystal-field excitations

3d\text{\ensuremath{-}}4f

Magnetic-field-induced transitions in multiferroic TbMnO 3 probed by resonant and nonresonant x-ray diffraction

coupling in the

Structural Distortion and Magnetic Order in the Intermetallic

\text{h-}R{\text{MnO}}_{3}