Ferroelectric and magnetic materials are a time-honoured subject of study and have led to some of the most important technological advances to date. Magnetism and ferroelectricity are involved with local spins and off-centre structural distortions, respectively. These two seemingly unrelated phenomena can coexist in certain unusual materials, termed multiferroics. Despite the possible coexistence of ferroelectricity and magnetism, a pronounced interplay between these properties has rarely been observed. This has prevented the realization of multiferroic devices offering such functionality. Here, we report a striking interplay between ferroelectricity and magnetism in the multiferroic TbMn2O5, demonstrated by a highly reproducible electric polarization reversal and permanent polarization imprint that are both actuated by an applied magnetic field. Our results point to new device applications such as magnetically recorded ferroelectric memory.

We have studied the magnetostructural phase diagram of multiferroic TbMn2O5 as a function of temperature and magnetic field by neutron diffraction. Dielectric and magnetic anomalies are found to be associated with steps in the magnetic propagation vector, including a rare example of a commensurate-incommensurate transition on cooling below 24 K, and in the structural parameters. The geometrically frustrated magnetic structure is stabilized by "canted antiferroelectric" displacements of the Mn3+ ions, an example of the magnetic Jahn-Teller effect. The Tb moments order ferromagnetically at low temperatures in an applied field, while the Mn magnetic structure is largely unchanged.

The thermal conductivity of the magnetically frustrated, ferroelectric YMnO3 exhibits an isotropic suppression in the cooperative paramagnetic state, followed by a sudden increase upon magnetic ordering. This unprecedented behavior without an associated static structural distortion probably originates from the strong dynamic coupling between acoustic phonons and low-energy spin fluctuations in geometrically frustrated magnets. The replacement of magnetic Ho for Y at the ferroelectrically active site results in an even larger effect, suggestive of the strong influence of multiferroicity.

We report neutron-diffraction measurements of the magnetic phase diagram of the colossal magnetoelectric DyMn 2 O 5. Our measurements reveal the magnetic origin of the complex dielectric anomalies in this material. Frustrated magnetic interactions result in a large density of low-energy magnetic states which can be selected by the application of relatively small magnetic fields. The unusual combination of magnetic frustration and strong magnetoelastic coupling is responsible for the remarkable changes of the dielectric properties of DyMn 2 O 5 in small applied magnetic fields.

We performed angle-resolved photoemission (ARPES) experiments with circularly polarized light and first-principles density functional calculation with spin-orbit coupling to study surface states of a topological insulator Bi2Se3. We observed circular dichroism (CD) as large as 30% in the ARPES data with upper and lower Dirac cones showing opposite signs in CD. The observed CD is attributed to the existence of local orbital-angular momentum (OAM). First-principles calculation shows that OAM in the surface states is significant and is locked to the electron momentum in the opposite direction to the spin, forming chiral OAM states. Our finding opens a new possibility for strong light-induced spin-polarized current in surface states. We also provide a proof for local OAM origin of the CD in ARPES.

In the present work, the effect of Dy3+ substitution on the structural and magnetic properties of CoFe2-xDyxO4 (x = 0.00 to 0.1 in step of 0.025) system synthesized by solution combustion method were investigated. The thermal decomposition process was investigated by means of differential and thermal gravimetric analysis that showed that the precursor could yield the final product after calcination above 600 °C. The phase purity and crystal lattice symmetry were estimated from X-ray diffraction studies. The microstructural features were observed by scanning electron microscopy that demonstrates the fine clustered particles with an increase of average grain size with Dy3+ content. The existence of constituent’s, i.e., Co, Fe, and Dy were authenticated by energy dispersive X-ray analysis. An infrared spectroscopy study shows the presence of two absorption bands in the frequency range around 590 cm−1 (ν1) and around 480 cm−1 (ν2); which indicate the presence of tetrahedral and octahedral group complexes, respectively, within the spinel lattice. Room temperature magnetization measurements showed that the saturation magnetization and hysteresis losses (coercivity) decreases with Dy3+ addition, which implies that these materials may be applicable for magnetic data storage and recording media.

We report on angle resolved photoemission spectroscopic studies on a parent topological insulator (TI), Bi2Se3. The line width of the spectral function (inverse of the quasi-particle lifetime) of the topological metallic (TM) states shows an anomalous behavior. This behavior can be reasonably accounted for by assuming decay of the quasi-particles predominantly into bulk electronic states through electron-electron interaction and defect scattering. Studies on aged surfaces reveal that topological metallic states are very much unaffected by the potentials created by adsorbed atoms or molecules on the surface, indicating that topological states could be indeed protected against weak perturbations.PACS numbers: 81.05. Uw, 63.20.kk, 73.20.At, TIs are materials with bulk gaps due to spin-orbit coupling. TIs are classified into 'weak TI' and 'strong TI' according to Z 2 topological invariants.2,3 Strong TIs have odd number of TM Dirac cones on the surface which is robust (protected) against disorder or impurities.TM states realized on the surface of a strong TI is important and could be useful.4,5 The properties of the TM are also set by the topological nature of the TI. The essential properties of TMs can be summarized as follows. First, electron spins in TM are locked into the momenta, forming spin chiral states 6 . Such spin chiral states are also well known in the field of surface science in terms of Rashba effects in surface states (for example, Sb (111) 7 , Bi (111) 8 and Au (111) 9 surfaces states). Second, back scattering is suppressed due to the spin chirality, 10 meaning relatively long quasi-particle life time. Third, metallic bands are protected against perturbations to the first order due to the topological nature. This point has yet to be experimentally observed.Experimental verification of the novel properties of TM is not only important in the fundamental aspect but also necessary for use of these materials for future applications. Due to the surface nature of the TM states, most of the experimental data thus far came from angle resolved photoemission (ARPES) 6,11-13 and to a less degree from scanning tunnelling microscopy (STM).10 By using ARPES, it was shown that there exist odd number of bands crossing the Fermi level in this class of materials.11,12 Moreover, spin resolved photoemission results show that the electron spins are indeed locked into the momentum and form spin chiral states.6 As for STM studies, a recent study shows suppression of back scattering, consistent with spin chiral states. 10Studies mentioned above are about existence and spin chiral states of TM and experimental verification of whether topological states are in general protected or not has not been discussed. Protected topological states should manifest themselves with long quasi-particle life time. In that regards, ARPES is an important tool because long quasi-particle life time should result in a sharp ARPES line-shape. In spite of the intensive recent efforts on TM electronic structure studies, photoemission lineshape issue...

We have observed coherent acoustic phonons in the hexagonal manganite LuMnO3 using two-color femtosecond optical pump-probe spectroscopy. The dependence of the oscillatory component of the photoinduced reflectivity on the probe wavelength and incident angle is consistent with a propagating strain pulse. Moreover, the frequency, dephasing, and phase of the oscillation are found to be temperature dependent. In particular, a large phase shift occurs in the vicinity of the Néel temperature (TN), which we relate to the temperature-dependent on-site Mn d–d transition that is coupled to antiferromagnetic ordering, as recently observed in optical conductivity measurements.