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Electrolyte gating technology has been widely used as an effective tool to study novel physics at complex oxide surfaces and interfaces. Certain emergent phenomena reported in electro-gated SrTiO3 (STO) surfaces are particularly interesting. Here, we report on the disparate electron transport behaviors of electrolyte-gated STO (001) and (110) oriented surfaces. In contrast to the anomalous transport from an insulating state to a Kondo-like state and then metallic states on the (001) surface, with increasing carrier density, the (110) surface always behaves as an insulating state. A comparison study suggests that the oxygen vacancies and localized Ti3+ ions on the (001) surface are scatter carriers, but no such defects are found on the (110) surface. This suggests that these surfaces are intrinsically insulating, and the observed anomalous effects are likely induced by the Ti3+ ions and oxygen vacancies introduced during electrolyte gating. This work sheds light on complicated phenomena in electrolyte-gated STO-based systems. [ABSTRACT FROM AUTHOR]

Antiferromagnetic spintronics has been receiving attention recently, while spin-texture dependent magnetoresistance (MR) represents one of the main mechanisms for magnetic data storage. In particular, sufficiently large MR with high operating temperatures would be highly required for advanced spintronic applications. In this work, we experimentally investigate the MR effect of well-known antiferromagnet α-Fe2O3 (hematite) in a single crystal form, which has the Morin transition temperature as high as Tm ∼ 260 K. It is revealed that the MR effect associated with the spin-texture re-alignment, i.e., the spin-flop from the out-of-plane direction (c axis) to the in-plane direction, driven by sufficiently low magnetic fields inclined along the [012] direction, reaches up to ∼2.5% at temperature T ∼ 250 K. The first-principles calculations suggest that this MR effect originates from the reduced bandgap due to the spin-flop and the finite spin–orbital coupling. The present work sheds light on the possibility of α-Fe2O3 as a favored MR-based candidate for near-room temperature spintronics. [ABSTRACT FROM AUTHOR]

The rare-earth double-perovskite R2CoMnO6 family has been reported to be promising multiferroics where the predicted ferroelectric polarization along the b-axis is induced by the Co2+/Mn4+ collinear magnetic order. In this work, we report our characterizations on the structural, magnetic, dielectric, and ferroelectric behaviors of flux-grown Y2CoMnO6 single crystals. A weak ferromagnetic transition with the Curie point TC ∼ 70 K is evident in combination with a remarkable magnetic hysteresis loop along the c-axis. The earlier reported dielectric anomaly at the magnetic transition is not detected in our single crystals. In addition, the peak of each electric current curve as a function of temperature, probed along different crystallographic directions, shows serious shifting with the temperature ramping rate, excluding the intrinsic ferroelectric contribution. The measured data are not in conformity with theoretical predictions and earlier experiments on polycrystalline samples. In addition, no reliable sign for magnetoelectric coupling can be detected. The present work seems to exclude the existence of magnetism-driven ferroelectricity in Y2CoMnO6. [ABSTRACT FROM AUTHOR]

The polar magnet, Fe2Mo3O8 (FMO), with linear magnetoelectric (ME) coupling, is a promising candidate for multiferroic applications in advanced spin devices. However, a giant magnetic bias (Hb) is needed for optimizing the inverse ME effect, i.e., electric field (E) modulation of magnetization (M), which is still a core issue. Herein, we utilize the chemical doping route to enhance the sensitivity of controlling the competitive magnetic interactions and/or multiferroic phases by means of introducing nonmagnetic Zn2+ ions into FMO crystals. Compared with FMO, the Zn-doped composition (Fe0.95Zn0.05)2Mo3O8 (FZMO) generates three metastable magnetic states in the middle of antiferromagnetic and ferrimagnetic states, along with obvious ferroelectric polarization. The inverse ME effect of FZMO is intact with a relative change of ΔM ≈ 0.06 μB/f.u. responding to an E value of ± 20 kV/cm at 52 K. Most interestingly, the exciting Hb is dramatically dropped to 0.8 T for FZMO from 5.1 T for FMO, which is in favor of the application of ME coupling. It is suggested that the perturbation of magnetic interactions via substituting specific sites by nonmagnetic ions plays a key role in decreasing the exciting Hb without deteriorating the inverse ME coupling in this polar M2Mo3O8 family. [ABSTRACT FROM AUTHOR]

The training effect has been systematically studied in exchange coupled NiFe2O4/NiO nanogranular system. Both exchange bias field (HEB) and vertical magnetization shifts (MShift) can be observed after the system field cooled from 350 K to low temperatures, which decrease monotonically through consecutive loop cycles. During this procedure, linear dependence between HEB and MShift is found for this system, revealing the critical role of the pinned uncompensated spins. With the increase of cooling field, the relative change of HEB becomes more pronounced, which shows that the rapid reduction of the pinned uncompensated spins for high cooling field. Moreover, the reduction of HEB becomes weakened with decreasing measured temperatures, which indicated the spin configuration at low temperatures possesses higher dynamic stability. The cooling field and temperature dependence on training effect is discussed in terms of the evolution of the metastable spin configurations at the interfaces and fitted by a recent theoretical model. [ABSTRACT FROM AUTHOR]

Using the first-principle calculations, we investigate in detail the structure instability resulting from softening of the polar zone-center phonon mode [ferroelectric (FE) instability] and nonpolar zone-boundary mode [antiferrodistortive (AFD) instability] in cubic BaZrO3 (BZO) under hydrostatic pressure P from -20 to 90 GPa. The hydrostatic pressure enhances the AFD instability, while it suppresses and then enhances the FE instability. A sequence of FE→cubic→AFD→AFD/FE phase transitions with increasing P is predicted. A careful examination of the pressure dependence of full phonon dispersions and interatomic force constants in real space reveals the microscopic key interactions in driving the transitions. With increasing pressure P, the drastically evolving short-range forces suppress the FE instability induced by the long-range dipole-dipole forces under low pressure, and enhance both the AFD and FE instability under high pressure. We investigate the dielectric properties of cubic BZO under hydrostatic pressure. The dielectric constant as a function of pressure shows a minimum contributed from the TO1 mode with the lowest frequency. We argue that this pressure dependence of the dielectric constant mainly originates from fluctuations of the SR forces. [ABSTRACT FROM AUTHOR]

The dielectric relaxation and magnetocapacitance effect of one-dimensional spin frustrated compound Ca3Co2O6 are investigated. The steplike magnetocapacitance effect is observed and one to one corresponds to the steplike magnetization. We explain this phenomenon from the spin configuration dependent dielectric response. The simulation results using the Monte Carlo method are in good agreement with experimental data at low temperature. The close correspondence between the magnetic and dielectric properties indicates that the coupling is the intrinsic character of Ca3Co2O. The steplike magnetocapacitance effect may find potential applications in data storage and sensors. [ABSTRACT FROM AUTHOR]

The conduction relaxations of polycrystalline La0.5Ca0.5Mn0.95Fe0.05O3 upon imposing rectangle electric current pulses (with minute time scale) are studied in details. We observe clear “overshooting” features of the conduction relaxation at both the front and rear edges of the current pulse so long as the pulse is sufficiently high. The Joule heating effect and the intrinsic stabilization of the ferromagnetic metal phase by the current pulse are linked in understanding our observations, and these effects may be applicable for resistance switching function. [ABSTRACT FROM AUTHOR]

The influence of a perpendicular electric field (F) on the optical properties of simple hexagonal and rhombohedral few-layer graphenes is studied through the tight-binding model. The electric-field-modulated absorption spectra depend on the stacking sequence. The low-energy absorption spectra of simple hexagonal few-layer graphenes exhibit the jumping structures in the absence or presence of an electric field. On the other hand, absorption spectra of rhombohedral few-layer graphenes show discontinuities and sharp peaks at F=0. Besides, the application of F affects the absorption spectra, generates new peaks, and changes peak position and peak height. The frequency of the peak is predicted to be closely associated with the stacking sequences and the field strength. Above all, the predicted absorption spectra could be verified by optical measurements. [ABSTRACT FROM AUTHOR]

We investigate the magnetization and electrical transport properties of Sm-based ternary magnetic bulk metallic glasses at low temperatures. A cluster spin-glass phase is evidenced below Tf∼25 K, which is probably ascribed to competition among the multifold magnetic interactions and intrinsic structural inhomogeneity, and further demonstrated by the magnetic hysteresis under field-cooling conditions. It is shown that the short-range magnetic clusters play as scattering centers for conductive electrons and result in a Kondo-like transport behavior in highly spin disordered Sm50Al25Co25 at low temperature. [ABSTRACT FROM AUTHOR]

The specific heat of La0.4Ca0.6MnO3 in bulk and nanoparticle (∼60 nm in grain size) forms was investigated. It is found that the charge-ordered state highly stabilized in the bulk samples can be significantly suppressed in the nanoparticle. The low temperature specific heat data reveal a Schottky-like anomaly at ∼5 K for the bulk sample, while a large electronic linear term (γ=17.8 mJ/mole K2) was identified for the nanoparticle samples. The magnetic measurements unveil the small magnetic entropy as low as ∼0.255 J/kg K and the possible existence of a Griffiths-like phase in the nanoparticle samples. We argue that the physics underlying the size effect is associated with the dimension-dependent interactions based on which the ferromagnetic/charge-ordering transition occurs. [ABSTRACT FROM AUTHOR]

Hybrid improper ferroelectrics have their electric polarization generated by two or more combined non-ferroelectric structural distortions, such as the rotation and tilting of Ti-O octahedral in the Ca3Ti2O7 (CTO) family. In this work, we prepare the high quality (010)-oriented CTO thin films on (110) SrTiO3 (STO) substrates by pulsed laser deposition. The good epitaxial growth of the CTO thin films on the substrates with the interfacial epitaxial relationship of [001]CTO//[001]STO and [100]CTO//[-110]STO is revealed. The in-plane ferroelectric hysteresis unveils an ultralow coercive field of ~5 kV/cm even at low temperature, nearly two orders of magnitude lower than that of bulk CTO single crystals. The huge difference between the epitaxial thin films and bulk crystals is most likely due to the lattice imperfections in the thin films rather than substrate induced lattice strains, suggesting high sensitivity of the ferroelectric properties to lattice defects. [ABSTRACT FROM AUTHOR]

Presents a study on the influence of crystal structure on the magnetoresistance of cobalt (Co)/chromium (Cr) multilayers. Characteristics of epitaxial Co/Cr multilayers; Definition of the giant magnetoresistance in multilayers; Effects due to the spin dependent scattering at the interfacial regions of the superlattice.

Electrolyte gating technology has been widely used as an effective tool to study novel physics at complex oxide surfaces and interfaces. Certain emergent phenomena reported in electro-gated SrTiO3 (STO) surfaces are particularly interesting. Here, we report on the disparate electron transport behaviors of electrolyte-gated STO (001) and (110) oriented surfaces. In contrast to the anomalous transport from an insulating state to a Kondo-like state and then metallic states on the (001) surface, with increasing carrier density, the (110) surface always behaves as an insulating state. A comparison study suggests that the oxygen vacancies and localized Ti3+ ions on the (001) surface are scatter carriers, but no such defects are found on the (110) surface. This suggests that these surfaces are intrinsically insulating, and the observed anomalous effects are likely induced by the Ti3+ ions and oxygen vacancies introduced during electrolyte gating. This work sheds light on complicated phenomena in electrolyte-gated STO-based systems. [ABSTRACT FROM AUTHOR]

We investigate epitaxial Pr0.65(Ca0.7Sr0.3)0.35MnO3 thin film grown on orthorhombic (110) NdGaO3 substrate which breaks the lattice symmetry and affects the phase separated ground state. As a result of the anisotropic substrate strain, giant in-plane magnetic and magnetotransport anisotropy are observed, which is related to the anisotropic coupling and competition between the double-exchange interaction and the Jahn-Teller distortion. Furthermore, the in-plane anisotropy shows a distinct enhancement near the metal-insulator transition, implying a significant contribution from the phase separation to the anisotropic transport behaviors. [ABSTRACT FROM AUTHOR]

We report the synthesis and characterization of an epitaxial heterostructure composed of multiferroic BiFeO3 and superconducting YBa2Cu3O7-δ thin films grown on (001) SrTiO3. Both the superconductivity of YBa2Cu3O7-δ and the ferroelectricity of BiFeO3 are retained in the heterostructure. Current density-electric field characteristics measured from 30 to 170 K suggest a Schottky-emission-like transport at the BiFeO3/YBa2Cu3O7-δ interface. Furthermore, the temperature dependence of the barrier height shows an anomalous enhancement at TC, indicating an intimate coupling between the multiferroic and the superconducting layers. [ABSTRACT FROM AUTHOR]

We investigate the effect of Ru doping on the dielectric and ferroelectric behaviors of polycrystalline Sr0.9Ba0.1TiO3. It is observed that the Ru doping significantly suppresses the ferroelectric mode, as evidenced by the Raman spectroscopy at various temperatures. The enhanced quantum fluctuation associated with the incorporation of Ru4+ at B site is demonstrated, which transforms Sr0.9Ba0.1TiO3 from the ferroelectric state into a typical quantum paraelectric state. [ABSTRACT FROM AUTHOR]

La0.4Ca0.6MnO3 nanoparticles of grain size as small as ∼20 nm are prepared and their magnetic behaviors are investigated in order to understand the size effect of the charge ordering in manganites. The highly stable charge-ordered state can be significantly suppressed upon reduction of the grain size down to nanometer scale, while the ferromagnetism is enhanced. The magnetic phase separation due to the competition between ferromagnetic state and charge-ordered state as well as the surface spin disordering is responsible for the spin-glass-like state at low temperature. [ABSTRACT FROM AUTHOR]

Using the first-principle calculations, we investigate in detail the structure instability resulting from softening of the polar zone-center phonon mode [ferroelectric (FE) instability] and nonpolar zone-boundary mode [antiferrodistortive (AFD) instability] in cubic BaZrO3 (BZO) under hydrostatic pressure P from -20 to 90 GPa. The hydrostatic pressure enhances the AFD instability, while it suppresses and then enhances the FE instability. A sequence of FE→cubic→AFD→AFD/FE phase transitions with increasing P is predicted. A careful examination of the pressure dependence of full phonon dispersions and interatomic force constants in real space reveals the microscopic key interactions in driving the transitions. With increasing pressure P, the drastically evolving short-range forces suppress the FE instability induced by the long-range dipole-dipole forces under low pressure, and enhance both the AFD and FE instability under high pressure. We investigate the dielectric properties of cubic BZO under hydrostatic pressure. The dielectric constant as a function of pressure shows a minimum contributed from the TO1 mode with the lowest frequency. We argue that this pressure dependence of the dielectric constant mainly originates from fluctuations of the SR forces. [ABSTRACT FROM AUTHOR]

The dielectric relaxation and magnetocapacitance effect of one-dimensional spin frustrated compound Ca3Co2O6 are investigated. The steplike magnetocapacitance effect is observed and one to one corresponds to the steplike magnetization. We explain this phenomenon from the spin configuration dependent dielectric response. The simulation results using the Monte Carlo method are in good agreement with experimental data at low temperature. The close correspondence between the magnetic and dielectric properties indicates that the coupling is the intrinsic character of Ca3Co2O. The steplike magnetocapacitance effect may find potential applications in data storage and sensors. [ABSTRACT FROM AUTHOR]

The conduction relaxations of polycrystalline La0.5Ca0.5Mn0.95Fe0.05O3 upon imposing rectangle electric current pulses (with minute time scale) are studied in details. We observe clear “overshooting” features of the conduction relaxation at both the front and rear edges of the current pulse so long as the pulse is sufficiently high. The Joule heating effect and the intrinsic stabilization of the ferromagnetic metal phase by the current pulse are linked in understanding our observations, and these effects may be applicable for resistance switching function. [ABSTRACT FROM AUTHOR]

We investigate the effect of Ru doping on the dielectric and ferroelectric behaviors of polycrystalline Sr0.9Ba0.1TiO3. It is observed that the Ru doping significantly suppresses the ferroelectric mode, as evidenced by the Raman spectroscopy at various temperatures. The enhanced quantum fluctuation associated with the incorporation of Ru4+ at B site is demonstrated, which transforms Sr0.9Ba0.1TiO3 from the ferroelectric state into a typical quantum paraelectric state. [ABSTRACT FROM AUTHOR]