Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userOrdering of localized electronic states in multiferroic TbMnO3: a soft X-ray resonant scattering study
138
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
Soft X-ray resonant scattering (XRS) has been used to observe directly, for the first time, the ordering of localized electronic states on both the Mn and Tb sites in multiferroic TbMnO$_3$. Large resonant enhancement of the X-ray scattering cross-section were observed when the incident photon energy was tuned to either the Mn $L$ or Tb $M$ edges which provide information on the Mn 3d and Tb $4f$ electronic states, respectively. The temperature dependence of the XRS signal establishes, in a model independent way, that in the high-temperature phase (28 K $leq$ T $leq$ 42 K) the Mn 3d sublattices displays long-range order. The Tb $4f$ sublattices are found to order only on entering the combined ferroelectric/magnetic state below 28 K. Our results are discussed with respect to recent hard XRS experiments (sensitive to spatially extended orbitals) and neutron scattering.
rate research
Read More
We report on an extensive investigation of the multiferroic compound TbMnO$_3$. Non-resonant x-ray magnetic scattering (NRXMS) revealed a dominant $A$-type domain. The temperature dependence of the intensity and wavevector associated with the incommensurate magnetic order was found to be in good agreement with neutron scattering data. XRS experiments were performed in the vicinity of the Mn $K$ and Tb $L_3$ edges in the high-temperature collinear phase, the intermediate temperature cycloidal/ferroelectric phase, and the low-temperature phase. In the collinear phase resonant $E1-E1$ satellites were found at the Mn $K$ edge associated with $A$-type but also $F$-type peaks. The azimuthal dependence of the $F$-type satellites (and their absence in the NRXMS experiments) indicates that they are most likely non-magnetic in origin. We suggest instead that they may be associated with an induced charge multipole. At the Tb $L_3$ edge resonant $A$- and $F$-type satellites ($E1-E1$) were observed in the collinear phase. These we attribute to a polarisation of the Tb 5$d$ states by the ordering of the Mn sublattice. In the cycloidal/ferroelectric phase a new set of resonant satellites appear corresponding to $C$-type order. These appear at the Tb $L_3$ edge only. In addition to a dominant $E1-E1$ component in the $sigma-pi^prime$ channel, a weaker component is found in the pre-edge with $sigma-sigma^prime$ polarization. Calculations of the XRS were performed using the $FDMNES$ code showing that the unrotated $sigma-sigma^prime$ component of the Tb $L_3$ $C$-type peaks appearing in the ferroelectric phase contains a contribution from a multipole that is odd with respect to both space and time, known in various contexts as the anapole.
Multiferroic TbMnO3 is investigated using x-ray diffraction in high magnetic fields. Measurements on first and second harmonic structural reflections due to modulations induced by the Mn and Tb magnetic order are presented as function of temperature and field oriented along the a and b-directions of the crystal. The relation to changes in ordering of the rare earth moments in applied field is discussed. Observations below T_N(Tb) without and with applied magnetic field point to a strong interaction of the rare earth order, the Mn moments and the lattice. Also, the incommensurate to commensurate transition of the wave vector at the critical fields is discussed with respect to the Tb and Mn magnetic order and a phase diagram on basis of these observations for magnetic fields H||a and H||b is presented. The observations point to a complicated and delicate magneto-elastic interaction as function of temperature and field.
Resonant x-ray scattering is performed near the Mn K-absorption edge for an epitaxial thin film of BiMnO3. The azimuthal angle dependence of the resonant (003) peak (in monoclinic indices) is measured with different photon polarizations; for the $sigmatopi$ channel a 3-fold symmetric oscillation is observed in the intensity variation, while the $sigmatosigma$ scattering intensity remains constant. These features are accounted for in terms of the peculiar ordering of the manganese 3d orbitals in BiMnO3. It is demonstrated that the resonant peak persists up to 770 K with an anomaly around 440 K; these high and low temperatures coincide with the structural transition temperatures, seen in bulk, with and without a symmetry change, respectively. A possible relationship of the orbital order with the ferroelectricity of the system is discussed.
X-ray resonant scattering has been used to measure the magnetic order of the Dy ions below 40K in multiferroic DyMn$_{2}$O$_{5}$. The magnetic order has a complex behaviour. There are several different ordering wavevectors, both incommensurate and commensurate, as the temperature is varied. In addition a non-magnetic signal at twice the wavevector of one of the commensurate signals is observed, the maximum intensity of which occurs at the same temperature as a local maximum in the ferroelectric polarisation. Some of the results, which bear resemblence to the behaviour of other members of the RMn$_{2}$O$_{5}$ family of multiferroic materials, may be explained by a theory based on so-called acentric spin-density waves.
Comprehensive x-ray scattering studies, including resonant scattering at Mn L-edge, Tb L- and M-edges, were performed on single crystals of TbMn2O5. X-ray intensities were observed at a forbidden Bragg position in the ferroelectric phases, in addition to the lattice and the magnetic modulation peaks. Temperature dependences of their intensities and the relation between the modulation wave vectors provide direct evidences of exchange striction induced ferroelectricity. Resonant x-ray scattering results demonstrate the presence of multiple magnetic orders by exhibiting their different temperature dependences. The commensurate-to-incommensurate phase transition around 24 K is attributed to discommensuration through phase slipping of the magnetic orders in spin frustrated geometries. We proposed that the low temperature incommensurate phase consists of the commensurate magnetic domains separated by anti-phase domain walls which reduce spontaneous polarizations abruptly at the transition.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
