Resistivity Of La0 Research Articles

Current induced effect on the resistivity in La0.8−xDyxNa0.2MnO3 monovalent doped manganites

The observation of electroresistance, ER effect in several substituted doped manganites which characterized the sensitivity of sample’s resistivity to the change of applied current was suggested can be enhanced by the presence of magnegtic inhomogenity. However, such effect is not well understood but the magnetic inhomogenity may influence the strength of ER related mechanism, hence current induced effect on the resistivity in monovalent doped La0.8−xDyxNa0.2MnO3 (x = 0.00–0.20) manganites prepared using solid state reaction method have been investigated to elucidate the matter. The ρ vs T curves shown that all samples exhibit smaller resistivity under higher applied current of 10 mA as compared to 5 mA of applied current in the wide temperature range of 30 K–300 K which led to ER effect. Measurement of ac susceptibility show that x = 0 sample exhibit ferromagnetic behaviour while both Dy substituted samples exhibit ferromagnetic to paramagnetic transition behavior with reduction in Tc values. Large ER effect with value of 130% at 300 K observed in ER vs. T curve for x = 0.1 sample, while for x = 0 the ER value is 9% indicates improved sensitivity of the Dy substituted sample towards electric field. While x = 0.20 sample exhibit double ER peaks which may related to presence of impurity phases. It is suggested Dy substitution induces magnetic inhomogeneities which favors formation of more filamentary conductive paths under the presence of high applied current thus enhanced the conduction process of charge carriers. The finding on the enhancement of ER effect indicates that the Dy substituted sample as potential candidates for spintronic-based devices.

Effect of microwave instant heating on magnetic, electric and microwave absorption properties of La0.7Na0.3MnO3

The emerging method of microwave (MW) heating was adopted to synthesize a phase pure La0.7Na0.3MnO3 from their oxide precursors. The MW power (P) used for heating the sample was varied from P = 1000 W to 1600 W to examine the effect of MW power on its physical properties. A well-crystalline single phase La0.7Na0.3MnO3 was achieved in 20 min of MW irradiation with P = 1600 W. The obtained grain sizes at P = 1000 W have grown bigger and densified while increasing the P = 1600 W. Growth in the grains was reflected in the resistivity of La0.7Na0.3MnO3 prepared at high P. As the P increases from 1000 W to 1600 W, the resistivity decreases drastically and the metal–insulator transition also becomes sharp at a temperature very close to TC whereas the ferromagnetic Curie temperature (TC) is least affected. The sample prepared at low P showed larger microwave absorption than the sample prepared under high P. These findings were correlated and discussed with the structural and morphological features acquired by microwave irradiation with different powers.

Effect of Hydrostatic Pressure on the Resistivity of La0.8Ag0.1MnO3 Ceramic near TC

Effect of Hydrostatic Pressure on the Resistivity of La0.8Ag0.1MnO3 Ceramic near TC

Tuning electronic transport through magnetic field and magnetoelectric coupling of multiferroic nanocomposites

Detailed analysis on structural, dielectric and ac electrical transport with dc magnetic field variation and magnetoelectric response are studied on semiconductor based multiferroic La0.7Sr0.3MnO3 - ZnO nanocomposites. The impedance data is observed to gradually enhance with magnetic field due to the strain developed in the sample, hampering the charge flow in the system. The nanocomposites display prominent magneto-impedance (∼87%) and magnetodielectric (∼35%) at room temperature. Nyquist plots are fitted utilizing two resistance-capacitor parallel circuits at varying magnetic fields demonstrating the governing role of La0.7Sr0.3MnO3 and ZnO grain boundaries. The grain boundary resistance of La0.7Sr0.3MnO3 decreases with field due to the depinning of domain walls from the grain boundary pinning centers and therefore improving the spin dependent transport mechanism while the grain boundary resistance of ZnO increases with field due to the scattering of the charge carrier. The magnetoelectric coupling investigated at a frequency of 1 kHz is accomplished in both longitudinal and transverse mode. Further, the magnetoelectric voltage induced by ac magnetic field executes a linear magnetoelectric response. The viewed magnetoelectric coupling might be in consequence of the field influenced magnetostriction of the piezomagnetic element of the composites. Such multiferroic material with tuning ac electrical property with magnetic field alongside magnetoelectric response can be pertinent in future solid-state microelectronic devices and sensor applications.

Description of the Colossal Magnetoresistance of La1.2Sr1.8Mn2O7 Based on the Spin-Polaron Conduction Mechanism in the Ferromagnetic Temperature Range

We have analyzed the resistance of La1.2Sr1.8Mn2(1 – z)O7 single crystal in magnetic fields from 0 to 90 kOe in the ferromagnetic temperature range. The observed magnetoresistance of La1.2Sr1.8Mn2O7 is described based on the spin-polaron conduction mechanism. The magnetoresistance is determined by the change in the sizes and magnetic moment directions of magnetic inhomogeneities (polarons). It is shown that the colossal magnetoresistance is ensured by an increase (along the magnetic field) of the polaron linear size. It is found using the method for separating the contributions of different conduction mechanisms to the magnetoresistance that the contribution to the magnetoresistance from the orientation mechanism at 80 K in low magnetic fields is close to 50%. With increasing magnetic field, this contribution decreases and becomes small in fields exceeding 30 kOe. The comparable contributions to the conductivity from the orientational and spin-polaron mechanisms unambiguously necessitate the inclusion of both conduction mechanisms in the magnetoresistance calculations. We have calculated the temperature variation of the polaron size (in relative units) in zero magnetic field and in a magnetic field of 90 kOe.

Polarization-induced electro resistance and magneto resistance in La0.67Ca0.33MnO3/BaTiO3 composite film

La0.67Ca0.33MnO3/BaTiO3 composite films have been grown on Nb-doped SrTiO3 substrates by the sol–gel method. The magnetic and ferroelectric properties in the composite films are investigated. A three-state memory is formed by applying a vertical electric field across the La0.67Ca0.33MnO3/BaTiO3 heterostructure, this behavior is attributed to the polarization-mediated resistive switching effect. In addition, the transport properties of La0.67Ca0.33MnO3 thin film can be modulated by an external magnetic field, a 10.3K shift of the metal insulator transition temperature is obtained with the change of applied magnetic field from 0T to 6T. Consequently, in La0.67Ca0.33MnO3/BaTiO3 heterostructure, the resistance behavior can be modulated by piezoelectric effect, ferroelectric polarization and magnetic field simultaneously.

The effect of La doping concentration on optical and electrical properties of LaxSr1-xTiO3 thin film fabricated by sol–gel process

Strontium titanate (SrTiO3), a typical wide-band-gap perovskite oxide, is a promising candidate for the application of thin film transistor (TFT). In this paper, the LaxSr1-xTiO3 thin films with different doping concentration are fabricated by sol–gel method. X-ray diffraction (XRD), scanning electron microscope (SEM), atomic force microscope (AFM), UV–Vis-NIR transmission spectroscopy and four point probe instrument are employed to characterize the crystal structure, surface profile, transmittance and resistivity of LaxSr1-xTiO3 thin films. The results show that LaxSr1-xTiO3 (x=0.5at.%, 1at.%, 1.5at.%, 2at.%, 4at.%, 6at.%, 8at.%, 10at.%) thin films are single SrTiO3 cubic phase after La doping. Additionally, the SEM and AFM observation reveal dense grains and smooth surface. LaxSr1-xTiO3 film possesses high transmittance in visible region. The conductivity of LaxSr1-xTiO3 thin films is improved tremendously after La doping. The resistivity of La0.04Sr0.96TiO3 is 11.7×10−3Ω·cm and its transmittance is 88.66%.

Abnormal colossal electroresistance in Ru-doped La0.225Pr0.4Ca0.375MnO3

We investigate the magnetic and transport properties of polycrystalline bulk La0.225Pr0.4Ca0.375Mn1−xRuxO3 (x ≤ 0.15). With a slight Ru substitution of Mn, the Curie temperature of ferromagnetic transition is raised, the thermal hysteresis of resistivity is suppressed, and two metal-insulator transitions (MITs) coming from different mechanisms are observed. Furthermore, we observe that the resistivity of La0.225Pr0.4Ca0.375Mn1−xRuxO3 (0.01 ≤ x ≤ 0.1) increases abnormally with external electric field, and external magnetic field can suppress such abnormal electroresistance. These results suggest that the slight doping of Ru greatly suppresses the antiferromagnetic charge-ordered insulating (AFM/COI) phase. The Mn3+-Ru4+ ferromagnetic super-exchange and possible Ru4+-Ru4+ AFM interaction are implied to explain the observed behaviors.

Large low field magneto-resistance and temperature coefficient of resistance in La0.8Ca0.2MnO3 epitaxial thin film

An epitaxial La0.8Ca0.2MnO3/LaAlO3 (LCMO/LAO) thin film was fabricated using the pulsed laser deposition (PLD) technique to evaluate the magnetoresistance (MR) and temperature coefficient of resistance (TCR). The LCMO film was about 200nm in thickness and appeared to have a strong out-of-plane texture. A giant value of MR 73% and 57% for both the ab-plane and in the c-directions respectively are obtained at 1.5T applied field. The values of TCR are about 14.2% K−1 and 11.5% K−1 for both the ab-plane and in the c-directions respectively in a wide temperature range. These results proved that La0.8Ca0.2MnO3/LaAlO3 (LCMO/LAO) thin film is a promising candidate of perovskites for novel electronic applications.

Spin fluctuation and small polaron conduction dominated electrical resistivity in La0.875Sr0.125MnO3 manganite nanostructures

The anomalous temperature-dependent electrical resistivity ρ(T) of La0.875Sr0.125MnO3 manganite nanoparticles (particle size 18 nm) is theoretically analysed. ρ(T) exhibits semiconducting phase in low-temperature regime (20 K < T < 53 K), shows a minima near 53 K and increases with T at high temperatures (53 K < T < 170 K). The resistivity in metallic phase (T > 53 K) is theoretically analysed by considering the strong spin-fluctuation effect, which is modelled using Drude-Lorentz type function. In addition to the spin fluctuation-induced contribution, the electron-phonon and electron-electron ρ e−e(T) = BT 2 contributions are also incorporated for complete understanding of experimental data. The contributions to the resistivity by inherent acoustic phonons (ρ ac) as well as high-frequency optical phonons (ρ op) were estimated using Bloch-Gruneisen (BG) model of resistivity. It is observed that the resistivity contribution due to electron-electron interaction shows typical quadratic temperature dependence. Spin fluctuation-induced resistivity is dominant over electron-electron and electron-phonon contributions in overall temperature range in the manganite nanoparticles. Resistivity in the semiconducting phase is discussed with small polaron conduction (SPC) model. SPC model consistently retraces the low-temperature resistivity behaviour (T < 53 K). Finally, the theoretically calculated resistivity compared with experimental data is found to be consistent in wide range of temperature.

Enhancement of temperature coefficient of resistivity in La0.67Ca0.33MnO3 polycrystalline ceramics

La0.67Ca0.33MnO3 polycrystalline ceramics with high temperature coefficient of resistivity (TCR) have been synthesized by the sol–gel method at the sintering temperature of 1450°C and in a sintering time range of 2h–24h. The micrographs of the ceramics reveal that the grains grow up from 2μm to about 10μm with increasing the sintering time. The optimization of the sintering time is found to be a simple and effective way to largely enhance the TCR values of the ceramics. The highest metal–insulator transition temperature Tp (272.5K) and the largest TCR (21.4%) were obtained in the ceramic sintered for 12h. The reduction of grain boundary and resistivity contributes to the enhancement of Tp and TCR values.

Effects of ferroelectric-poling-induced strain on magnetic and transport properties of La0.67Ba0.33MnO3 thin films grown on (111)-oriented ferroelectric substrates

La0.67Ba0.33MnO3 thin films were epitaxially grown on (111)-oriented 0.31Pb(In1/2Nb1/2)O3-0.35Pb(Mg1/3Nb2/3)O3-0.34PbTiO3 ferroelectric single-crystal substrates. During ferroelectric poling and polarization rotation, the resistance of La0.67Ba0.33MnO3 films tracks the electric-field-induced in-plane strain of substrates effectively, implying strain-mediated coupling. Upon poling along the [111] direction, ferromagnetism is suppressed for T &amp;lt; 175 K, but enhanced for T &amp;gt; 175 K, which is explained by magnetoelastic coupling that modifies the film's magnetic anisotropy. Our findings also show that the magnetic field has an opposite effect on the strain-tunability of resistance [i.e.,(ΔR/R)strain] above and below the Curie temperature TC, which is interpreted within the framework of phase separation.

Prediction of the Magneto-Resistance of La&lt;sub&gt;0.65&lt;/sub&gt;Ca&lt;sub&gt;0.35&lt;/sub&gt;MnO&lt;sub&gt;3&lt;/sub&gt; and La&lt;sub&gt;0.8&lt;/sub&gt;Sr&lt;sub&gt;0.2&lt;/sub&gt;MnO&lt;sub&gt;3&lt;/sub&gt; via Temperature and Magnetic Field

The resistance associated with temperature and magnetic field is a crucial parameter in researching the physical properties of the Perovskite-type manganites. To find out a suitable method to predicting the resistance of La0.65Ca0.35MnO3 and La0.8Sr0.2MnO3 in the process from paramagnetic phase to the ferromagnetic phase via the temperature and the magnetic field was the aim of this paper. By the nonlinear fitting, an appreciated analytic expression showing the temperature-dependence resistance both less or higher than the metal-insulator transition temperature,Tc, at different magnetic field was put forward. All of the nonlinear fitting between the measured and the calculated data were so satisfied that the minimum correlation coefficient is below 0.9997, the average relative errors do not exceed 1.0%.

Analysis of the Effect of Temparature on the Resistivity of Nanocrystalline La&lt;sub&gt;0.7&lt;/sub&gt; Ba&lt;sub&gt;0.3&lt;/sub&gt;MnO&lt;sub&gt;3&lt;/sub&gt; Powders

A Systematic investigation on structural, electrical, microstructure and compositions properties of La0.7Ba0.3MnO3 powder, prepared by a standard solid state reaction method, has been undertaken. The XRD pattern showed that the as prepared LBMO material was in single-phase rhombohedral structure. The electrical properties of as grown powders were carried out using standard four probe technique. The influence of dc biasing current on temperature dependence of resistance of La0.7Ba0.3MnO3 powder was reported. From electrical data it was observed that the electrical resistance decreased with bias current indicating the alignment of spins and increase in spin stiffness coefficient and decreasing the resistance at metal-insulator transition temperature (TMI). The surface morphology of the samples was studied by scanning electron microscope. From scanning electron micrographs, granular features were observed with average grain size of ~20nm.

Annealing effect on temperature coefficient of resistivity in La1−xSrxMnO3 ceramics

Abstract We investigated annealing effects of La1−xSrxMnO3 (x = 0–0.6) on electrical resistivity and the temperature coefficient of resistivity (TCR). The annealed samples’ resistivity was lower than those of non-annealed samples. For example, annealing changed the resistivity of x = 0.3 at 25 °C from 4.50 × 10−5 to 3.71 × 10−5 Ω m. Remarkable difference in TCR was observed after annealing, for x = 0.3, 0.45, and 0.5. For x = 0.3, the TCR after annealing was 4000 ppm/°C, which was 1250 ppm/°C greater than that before annealing. We investigated (1) crystal phase, (2) Mn average valence, (3) Mott insulator–metal transition temperature, and (4) microstructure. The microstructure was remarkably varied for annealed x = 0.3 and 0.5. The average grain size of the x = 0.3 increased from 1.60 up to 2.38 μm. Results show that annealing affects resistivity and TCR because of grain growth during annealing.

Large photoinduced conductivity reduction in thin films of metallic ferromagnetic manganites

This paper reports on a study of photoinduced resistivity changes in thin films of ferromagnetic metallic (FMM) manganites. We have observed a significant increase of resistance in La0.7Ba0.3MnO3 thin film under continuous wave argon ion laser illumination presumably associated with photoinduced demagnetization. Strong dependence of resistance on thermal/illumination history is consistent with the coexistence of two phases: ferromagnetic metallic phase and photoinduced less conductive phase.

Variations in the electrical resistivity of La0.67Ca0.33MnO3 films and induced interconversions of ferromagnetic and nonferromagnetic inclusions in their bulk

A significant (similar to 1.8%) positive unit between the parameters of the crystal lattice is the reason of tetragonal distortion (a (aSyen)/a (aEuro-) a parts per thousand 1.04) and reduction in the volume of the unit cell of La(0.67)Ca(0.33)MnO(3) films (15 nm) quasicoherently grown on the (001) surface of a LaAlO(3) substrate. The films consist of single-crystal blocks with the lateral size of 30-50 nm. The atomically smooth LaAlO(3)-La(0.67)Ca(0.33)MnO(3) interphase boundary has no misfit dislocations. At T = 4.2 K, the transformation of nonferromagnetic phase inclusions into ferromagnetic ones in a constant magnetic field H is accompanied by a stable reduction in the electrical resistivity rho of manganite films with time, so that the curve rho(t) is well approximated by the relationship rho(t) similar to rho(1)(t - t (0))(1/2), (where t (0) is the time for establishment of the specified value (mu(0) H = 5 T) of the magnetic field and rho(1) is a coefficient independent of H). The magnetocrystalline anisotropy due to the elastic deformation of films by the substrate and stratification of electronic phases are the reasons of the distinct hysteresis in the dependences rho(mu(0) H, T 0 -> -5 T -> 0 -> 5 T. At T = 50 K and mu(0) H = 0.4 T, the magnetoresistance MR = 100% [rho(mu(0) H) - rho(mu(0) H = 0)]/rho(mu(0) H = 0) of LCMO films attains 150%.

Wide range magnetoresistance and high temperature coefficient of resistance in La0.7Sr0.3−xAgxMnO3 system

We report observation of composition and process parameter dependant wide range magnetoresistance and high temperature coefficient of resistance in La0.7Sr0.3−xAgxMnO3 (0 ≤ x ≤ 0.3) system. The polycrystalline samples synthesized through solid state reaction method exhibited rhombohedral structure with systematic change in lattice parameters. The samples with x ≤ 0.2 showed metallic behavior below room temperature. A broad metal-insulator transition is observed for x = 0.3, which becomes sharp for the samples sintered at high temperature. The broad transition resulted in magnetoresistance (MR) value around 35% over a wide temperature range whereas the sharp transition results in MR value as high as 85%. The temperature coefficient of resistance value of 11% is seen as a consequence of sharp transition. The magnetic transition was sharp for the samples sintered at high temperature.

Strain response of La0.7Sr0.3CoO3 epitaxial thin films probed by SrTiO3 crystalline microcantilevers

We investigate the effect of tensile strain on the resistivity of La0.7Sr0.3CoO3 thin films grown on SrTiO3 microcantilevers. Strain is applied by bending the microcantilevers both mechanically through an atomic force microscope tip and electrostatically. A strain gauge factor of 12 is observed, similar to the value measured for manganite thin films. Such low value evidences the role of extrinsic effects in the cobaltites giant gauge factor observed by other authors.

Dynamics of a robust photo-induced insulator–metal transitiondriven by coherent and broad-band light in epitaxial films ofLa0.625 − yPryCa0.375MnO3

A dramatic drop of ≈5 orders of magnitude in the resistance (R) ofLa0.175Pr0.45Ca0.375MnO3 epitaxial films upon exposure to optical photons derived from bothcontinuous and pulsed lasers, as well as broad-band sources at temperatures(T) < 30 K is reported. The strength of change is a sensitive function of both the incident photon flux andtemperature. Under isothermal conditions the photo-generated low resistance state persistseternally after removal of light. This non-equilibrium state is metallic, as revealed by the positivedR/dT forT ≤ Tp (≈120 K). This electrically conducting state is presumably ferromagnetic asTp coincides with the temperature where a weak ferromagnetism sets in on cooling the insulatingfilm from room temperature. To rule out the possibility of photon-induced local heating ofthe sample as a mechanism of the observed effects, photo-illumination experiments wereperformed under identical conditions on thin films of two non-charge-ordered manganitesdeposited on substrates of similar thermal conductivity. Our model for the observed transitionencompasses a global charge-ordered state in which ferromagnetic metallic clusters of fractionp much less than thecritical fraction pc for percolation exists at low temperatures. Photo-inducedmelting of the charge-ordered state increases this fraction beyondpc in a cumulative manner as successive pulses of light fall on the sample.