T. Zou

Excess-hole induced high temperature polarized state and its correlation with the multiferroicity in single crystalline DyMnO3

Controlling the ferroelectricity and magnetism in multiferroic materials has been an important research topic. We report the formation of a highly polarized state in multiferroic DyMnO3 single crystals which develops well above the magnetic transition temperatures, and we attribute it the thermally stimulated depolarization current effect of excess holes forming Mn4+ ions in the system. We also show that this high temperature polarized state intimately correlates with the lower temperature ferroelectric state that is induced by the incommensurate spiral magnetic order of Mn spins. This study demonstrate an efficient approach to tune the multiferroicity in the manganite system.

Tuning the ferroelectric state in multiferroic TbMnO3 single crystal by a trapped-charge-induced internal electric field

The pyroelectric current effects in multiferroic TbMnO3 single crystal are reinvestigated in a wide temperature range. We report a pyroelectric current peak occurring around T = 107 K, which is much higher than the magnetic phase transition temperatures, after poling the sample from T ≥ 60 K to low temperatures, and we attribute it to the thermal release of trapped-charges in TbMnO3. We also show that the trapped-charges form a strong internal electric field that remarkably controls the ferroelectric polarization state induced by the cycloidal Mn3+ spins at lower temperature.

Colossal Magnetoresistance in a Mott Insulator via Magnetic Field-Driven Insulator-Metal Transition.

We present a new type of colossal magnetoresistance (CMR) arising from an anomalous collapse of the Mott insulating state via a modest magnetic field in a bilayer ruthenate, Ti-doped Ca_{3}Ru_{2}O_{7}. Such an insulator-metal transition is accompanied by changes in both lattice and magnetic structures. Our findings have important implications because a magnetic field usually stabilizes the insulating ground state in a Mott-Hubbard system, thus calling for a deeper theoretical study to reexamine the magnetic field tuning of Mott systems with magnetic and electronic instabilities and spin-lattice-charge coupling. This study further provides a model approach to search for CMR systems other than manganites, such as Mott insulators in the vicinity of the boundary between competing phases.

Field-induced magnetic phase transitions and memory effect in bilayer ruthenate Ca3Ru2O7 with Fe substitution

Bilayer ruthenate Ca3(Ru1-xFex)2O7 (x = 0.05) exhibits an incommensurate magnetic soliton lattice driven by the Dzyaloshinskii-Moriya interaction. Here we report complex field-induced magnetic phase transitions and memory effect in this system via single-crystal neutron diffraction and magnetotransport measurements. We observe first-order incommensurate-to-commensurate magnetic transitions upon applying the magnetic field both along and perpendicular to the propagation axis of the incommensurate spin structure. Furthermore, we find that the metastable states formed upon decreasing the magnetic field depend on temperature and the applied field orientation. We suggest that the observed field-induced metastability may be ascribable to the quenched kinetics at low temperature.

Non-Fermi surface nesting driven commensurate magnetic ordering in Fe-doped Sr2RuO4

Sr

Up-up-down-down magnetic chain structure of the spin- 12 tetragonally distorted spinel GeCu2O4

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Unusual UUDD magnetic chain structure of the spin-1/2 tetragonally distorted spinel GeCu2O4

RuO

Up-up-down-down magnetic chain structure of the spin- 1 2 tetragonally distorted spinel GeC u 2 O 4

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Unusual interlayer quantum transport behavior caused by the zeroth Landau level in YbMnBi 2

, an unconventional superconductor, is known to possess an incommensurate spin density wave instability driven by Fermi surface nesting. Here we report a static spin density wave ordering with a commensurate propagation vector

Weak ferromagnetism of Cu x Fe 1 + y As and its evolution with Co doping

q_c