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Mechanical force has been found to be an alternative way to non-electrically switch the polarization of ultrathin ferroelectric films owing to the flexoelectric effect. Reducing the required force for switching is desirable for a low risk of damage to both sample and tip. Here, the strain dependence of mechanical threshold force has been studied in ultrathin PbZr0.2Ti0.8O3 films. The mechanical threshold force for polarization reversal reduces remarkably by a factor of ~5 with decreasing the compressive strain, associated with a reduction of coercivity and tetragonality. We attributed such behavior to the reduction of switching barrier and remnant polarization. Our work provides a route to realize ultra-low mechanical writing force for non-volatile memory applications. [ABSTRACT FROM AUTHOR]

We investigate the effect of biaxial strain on the switching of ferroelectric thin films. The strain state of epitaxial PbZr0.52Ti0.48O3 films is controlled directly and reversibly by the use of piezoelectric Pb(Mg1/3Nb2/3)0.72Ti0.48O3 (001) substrates. At small external electric fields, the films show switching characteristics consistent with a creep-like domain wall motion. In this regime, we find a huge decrease of the switching time under compressive strain. For larger external electric fields, the domain wall motion is in a depinning regime. The effect of compressive strain is more moderate in this region and shows a reduction in the switching kinetics. [ABSTRACT FROM AUTHOR]

We investigate the structure and magnetic properties of thin films of the LaCoO3 compound. Thin films are deposited by pulsed laser deposition on various substrates in order to tune the strain from compressive to tensile. Single-phase (001) oriented LaCoO3 layers were grown on all substrates despite large misfits. The tetragonal distortion of the films covers a wide range from -2% to 2.8%. Our LaCoO3 films are ferromagnetic with Curie temperature around 85 K, contrary to the bulk. The total magnetic moment is below 1 μ B/Co3+, a value relatively small for an exited spin-state of the Co3+ ions, but comparable to values reported in literature. A correlation of strain states and magnetic moment of Co3+ ions in LaCoO3 thin films is observed. [ABSTRACT FROM AUTHOR]

Electron emission from [Pb(Mg1/3Nb2/3)O3]0.72 [PbTiO3]0.28 (PMN-PT) thin ferroelectric single crystals is reported at ultralow voltages down to 20V per 400μm thickness, and for up to 109 switching cycles. The PMN-PT samples were prepared with split gold top electrodes exhibiting a 25μm wide gap region. Applying a sinusoidal voltage between the two top electrodes and the bottom electrode initiated electron emission from the gap region. The emitted electrons were collected under UHV conditions using two single electron counters arranged under an angle of 90°. Two emission regimes have been identified. Both are attributable to weak electron emission, however, clearly separated by the onset of complete ferroelectric polarization switching. This is also confirmed by recording nanoscale ferroelectric hysteresis loops by means of piezoresponse force microscopy. The emitted electrons are found to have a broad energy distribution with the maximum kinetic energies reaching 110 and 50 eV for applied switching voltages of 140 and 110 V, respectively. Our results confirm that polarization reversal is the governing mechanism behind the electron-emission process in the thin PMN-PT samples. Also, the applied electric field strengths needed to trigger electron emission from the PMN-PT crystals are about 10 times lower compared to most other (ferroelectric) materials reported in the literature. [ABSTRACT FROM AUTHOR]

We report the charge state modification effects at the Mn site on the ground state properties of colossal magnetoresistive manganites. Ta5+ substitution results in an appreciable increase in the lattice parameters and unit cell volume due to increased Mn3+ concentration. The ferromagnetic-metallic ground state modifies to a cluster glass insulator for $x \geqslant 0.05$ . The reduction in the transition temperatures with increasing x is ∼39 K/at.%. Besides the modification of majority carrier concentration due to increased Mn3+ concentration and enhanced local structural effects, the local electrostatic potential of the substituent seems to contribute to the unusually strong reduction of the transition temperatures of the compounds. Thermo magnetic irreversibility just below Curie temperature (Tc), non-saturation of magnetization, two distinct magnetic transitions in ac susceptibility in an appropriate static field: close to Tc and other at low temperature (the spin freezing temperature (Tg)) and non-stationary dynamics with a characteristic maximum in the magnetic viscosity close to Tg confirm a cluster glass state for $x \geqslant 0.05$ . These results find additional support from a linear low temperature magnetic specific heat of x = 0.10 with a characteristic broad maximum close to Tg. [ABSTRACT FROM AUTHOR]

We report the charge state modification effects at the Mn site on the ground state properties of colossal magnetoresistive manganites. Ta5+ substitution results in an appreciable increase in the lattice parameters and unit cell volume due to increased Mn3+ concentration. The ferromagnetic-metallic ground state modifies to a cluster glass insulator for $x \geqslant 0.05$ . The reduction in the transition temperatures with increasing x is ∼39 K/at.%. Besides the modification of majority carrier concentration due to increased Mn3+ concentration and enhanced local structural effects, the local electrostatic potential of the substituent seems to contribute to the unusually strong reduction of the transition temperatures of the compounds. Thermo magnetic irreversibility just below Curie temperature (Tc), non-saturation of magnetization, two distinct magnetic transitions in ac susceptibility in an appropriate static field: close to Tc and other at low temperature (the spin freezing temperature (Tg)) and non-stationary dynamics with a characteristic maximum in the magnetic viscosity close to Tg confirm a cluster glass state for $x \geqslant 0.05$ . These results find additional support from a linear low temperature magnetic specific heat of x = 0.10 with a characteristic broad maximum close to Tg. [ABSTRACT FROM AUTHOR]

Abstract: Heteroepitaxial bilayers of La0.7Sr0.3MnO3/PbZr0.52Ti0.48O3 on SrTiO3(100) have been grown by off-axis pulsed laser deposition (PLD). Both the ferromagnetic and the ferroelectric films are of high structural and functional (magnetic, ferroelectric) quality. A field effect transistor like device structure has been utilized for the investigation of electrical field-induced resistance modulations of the manganite also showing colossal magnetoresistance (CMR). Such devices are known to show an electrical field effect of up to 20% at 300K in ultrathin layers of manganites with lower doping level (10–20%). The resistance modulation of the La0.7Sr0.3MnO3 channel layers of d =8–200nm thickness is small at 300K, with maximum value of 0.2% for d =8nm. The results are discussed with respect to the phase diagram of La0.7Sr0.3MnO3. [Copyright &y& Elsevier]

Abstract: For the first time, the effect of Ta5+ substitution at the Mn site of La0.67Ca0.33MnO3 compound is reported. A significant increase in lattice parameters and unit cell expansion indicate larger structural modification upon substitution. The ferromagnetic-metallic ground state is modified to a cluster glass insulator for . The observed suppression of the ferromagnetic transition temperature T c of ∼39K/at% might be the highest reported in Mn-site substituted La0.67Ca0.33MnO3. The well-known effects of changed carrier density, larger average ionic radius at Mn site and dilution of Mn sublattice appear insufficient to explain this strong suppression of T C. [Copyright &y& Elsevier]

Two sets of accessions were sampled from a natural population f Hordeum spontaneum at Shelomi, Israel, viz: 100 ears along a transect at intervals of 1-1.5 m and 10 ring clusters of 10 ears each, circling each 10th plant of the transect. Single ear progenies were tested for banding patterns of 5 allozyme loci; in addition, hordein banding and field reaction against powdery mildew has been determined. 56 allozyme genotypes and 13 hordein patterns were determined. Most of the progenies showed susceptible to moderately susceptible infection types and high frequencies of low infection grade (slow mildewing). For all characters spatial grouping was found in plants derived from neighbouring transect parents. This was even more pronounced in the ring clusters. Reactions to mildew infection appeared to be closely correlated with hordein banding. In addition, accessions showing hypersensitive reactions carried excessive frequencies of a certain allele of the Est-1 locus. [ABSTRACT FROM AUTHOR]

Multiple quantum nuclear magnetic resonance (NMR) transitions were observed on polarizedLi nuclei, which were produced by capture of polarized neutrons in a single crystal of LiTaO. The asymmetricLi β-radiation distribution was used for the detection of NMR. A quadrupole moment ratio ¦ Q(Li)/ Q(Li)¦=0.78(1) was determined. Saturation of multiple quantum transitions in nuclear radiation detected NMR may lead to a reduction in measuring time of up to two orders of magnitude, as compared to single quantum detection methods. The measured spectra agree well with an exact lineshape calculation. The same measurements were also performed on a LiTaO powder sample. This was done to test a method to obtain quadrupole coupling constants from high field NMR multiple quantum powder patterns, which are easily detectable, also for higher nuclear spins. This latter method may be applicable also to conventional NMR detection techniques. [ABSTRACT FROM AUTHOR]

The ferroelectric polarization loop of an epitaxial BiFeO3 film on a piezoelectric substrate has been investigated as a function of continuously and reversibly varied biaxial strain of [variant_greek_epsilon]=0.36%-0.51%. Over this range, the ferroelectric coercive field (EC) at 80 K increases reversibly by 36% with the increasing tensile strain. In contrast, phase-field simulations predict the opposite trend of dEC/d[variant_greek_epsilon]<0. Therefore, we attribute the observed EC([variant_greek_epsilon]) dependence to the strain dependence of domain dynamics, which are not included in thermodynamic models. The strain dependence of the remanent polarization agrees with previous results. [ABSTRACT FROM AUTHOR]

We have determined the energy level alignment at interfaces between La0.7Sr0.3MnO3 and two typical organic semiconductors, copper-phthalocyanine and α-sexithiophene. La0.7Sr0.3MnO3 thin films have been grown using pulsed laser deposition and subsequently ex situ cleaned before the organic materials have been deposited. This procedure is often applied in the fabrication of organic devices. We show that under these conditions the interfaces are free from chemical interaction and characterized by a short range interface dipole and large charge injection barriers. [ABSTRACT FROM AUTHOR]

The spin-polarized electric transport in ferromagnetic La0.7Sr0.3MnO3 films on piezoelectric substrates with etched steps has been investigated. The Pb(Mg1/3Nb2/3)0.72Ti0.28O3 substrate is strained reversibly by application of electric voltage. This includes strain control in film junctions formed at step edges. The film resistance (R) is very sensitive to both strain and magnetic field in a wide temperature range, 30 K

Hexagonal, twin-free HoMnO3 (0001) films of 25–240 nm thickness were grown epitaxially on Y2O3:ZrO2(111) substrates using pulsed laser deposition. Ferroelectric polar order and Mn3+ antiferromagnetism were observed by optical second harmonic generation. Magnetization data reveal Ho3+ ordering which is, with subtle deviations, similar to that of bulk crystals. However, three phase transitions below 6 K and thermal hysteresis of magnetization at T<42 K were detected. [ABSTRACT FROM AUTHOR]

Epitaxially grown La0.7Sr0.3MnO3 thin films show resistance modulations induced by the inverse piezoeffect of the employed Pb(Mg1/3Nb2/3)O3-PbTiO3(001) (PMN-PT) substrates. The in-plane strain state of the films can continuously be tuned by application of a piezovoltage to PMN-PT. The lattice deformation of a PMN-PT(001) substrate was quantified by x-ray measurements under an electric field. Variation of in-plane lattice parameters by ∼0.06% reversibly changes the resistance of the manganite films by up to 9% at 300 K and shifts the magnetic Curie temperature. Films of different thicknesses from 50 to 290 nm, offering different as-grown strain states, have been studied. [ABSTRACT FROM AUTHOR]

Epitaxial ferroelectric-ferromagnetic field effect devices of PbZr0.52Ti0.48O3/La0.7Sr0.3MnO3 (PZT/LSMO) with narrow manganite channels (<=7 nm) show butterflylike hysteretic resistance modulations (ΔR) which are commensurate with strain variation from inverse piezoelectric effect of PZT. Based on the type of observed resistance hysteresis loops, contributions from electric field effect and strain effect have been distinguished for devices with varied channel thickness. The strain-induced ΔR decreases with increasing channel thickness. The ΔR from field effect is low in the LSMO channels with 30% Sr doping. [ABSTRACT FROM AUTHOR]

We have studied the transport properties of mechanically stable Fe3O4 and La0.7Sr0.3MnO3 nanoconstrictions patterned by focused ion-beam milling. The magnetoresistance decreases with the square of the applied voltage and scales with the resistance of the constriction, with values up to 8000% for magnetite and 100% for La0.7Sr0.3MnO3. These results are interpreted within a model for domain-wall magnetoresistance. Some samples exhibit electrical hysteresis with discrete changes of resistance that disappear in the presence of a magnetic field, indicating domain-wall displacement driven by a spin-polarized current. [ABSTRACT FROM AUTHOR]

The complex dielectric function of La[SUB0.7]Ca[SUB0.3]MnO[SUB3] films with various thicknesses and on different substrates was determined by the analysis of measured ellipsometric parameters. The temperature-dependent redistribution of low-energy spectral weight shows that the metallicity is developed gradually below an onset temperature that is found to depend strongly on global and local strain properties, not on film thickness alone. Importantly, the 2nm film shows no metallic conduction but an optical charge-carrier response below 240 K. This suggests that ultrathin films are characterized by phase separation and a percolation-type transition. [ABSTRACT FROM AUTHOR]