Magnetoresistive Properties Of La0 Research Articles

Effect of the glycerol dispersant on the structure, electrical transport and magnetoresistive properties of La0.67Ca0.33MnO3 ceramics prepared by the sol-gel routine

In this paper, the sol-gel technique is employed to synthesize polycrystalline La0.67Ca0.33MnO3 (LCMO) ceramics, where methanol is chosen as the solvent. The crystal structure, morphology, as well as electrical and magnetoresistive properties were examined. Moreover, the effect of amount of the dispersant glycerol on the properties of LCMO ceramics is studied. X-ray diffraction (XRD) results showed that all samples crystallized in single phases with orthogonal perovskite structure (pnma space group), without any detectable impurity phases. Results reveal that the grain size of LCMO ceramics exhibits an initial increase followed by a decrease, accompanied by a similar behavior in the temperature coefficient of resistance (TCR) and magnetoresistance (MR). When the volume ratio of glycerol and methanol reached 2 %, the grain size is determined to be 7.30 μm, with TCR value of 25.02 % K−1 at T= 263.2 K, and MR value recorded at 55.40 %. The study elucidates the influence of glycerol on LCMO polycrystalline ceramics and optimize the fabrication process, thereby improve the electric transport property and magnetoresistance.

Effect of Bi-doping on structural, magneto-caloric and magneto-resistive properties of La0.67- xBixCa0.33MnO3 perovskites

We report the doping effect of Bi on structural, magnetic and magneto-resistive properties of nanocrystalline La0.67-xBixCa0.33MnO3 (x = 0, 0.05, 0.1) (LBCMO) samples. Rietveld refinement of the X-ray diffraction (XRD) patterns revealed that all the three samples crystallize into orthorhombic crystal structure having Pbnm space group. The average crystallite size was calculated using Debye Scherer's formula and the crystallite size varies from 25 to 30 nm. Scanning electron microscopy (SEM) images shows that the particles are spherical in nature and distributed uniformly. The temperature dependent magnetization data infers that all the three samples undergo paramagnetic to ferromagnetic (PM-FM) phase transition with transition temperature (Tc) ~245 K, 250 K and 230 K upon cooling. La0.67Ca0.33MnO3 (LBCMO1), La0.62Bi0.05Ca0.33MnO3 (LBCMO2) samples exhibit second order magnetic phase transition, whereas La0.57Bi0.1Ca0.33MnO3 (LBCMO3) sample exhibit first order like transition. The maximum magnetic entropy changes |ΔSMmax| were calculated for nanocrystalline LBCMO samples using thermodynamic relations and the values were 3.73 Jkg−1K−1, 4.72 Jkg−1K−1 and 4.47 Jkg−1K−1 respectively, where field change was μoH = 5 T. As a consequence of temperature dependence of electrical resistivity, data shows metallic behavior before metal-semiconductor transition temperature (TMS) and semiconducting behavior after TMS. The magnetic field dependent electrical resistivity data reveals a huge change in resistivity near TMS and the maximum magnetoresistance (MR) value around ~60% for an applied field of 5T around the TMS for LBCMO3 sample. The coexistence of magnetocaloric effect and moderately high value of magnetoresistance makes the studied samples promising for multifunctional device applications near its critical temperature.

Effect of Na-doping on structural, electrical, and magnetoresistive properties of La0.7(Ag0.3-xNax)0.3MnO3 polycrystalline ceramics

In this work, perovskite manganites, La0.7(Ag0.3-xNax)0.3MnO3 (LANMO, x = 0, 0.05, 0.1, 0.15, and 0.2), were synthesized using facile sol-gel method. Structural, electrical, and magnetoresistive (MR) properties of LANMO samples with different sodium contents were investigated. XRD and Rietveld refinement revealed that all samples crystallized in distorted rhombohedral system with R3‾c space group. The doping of sodium increased average particle sizes and A-site cation vacancies and also reduced formal charges of Mn. Electrical transport properties showed that peaks for temperature coefficient of resistance (TCR) and corresponding temperatures (Tk) improved significantly due to increased Na content. TCR and MR values of 10.4% K−1 and 24.5% for x = 0.1 were obtained at room temperature (297.1 and 299.2 K, respectively). Results suggest that these LANMO ceramics are potentially attractive candidates for applications in room-temperature infrared detector.

Magnetoresistive properties of cerium doped La0.7Ca0.3MnO3 manganites

In this work, the effect of doping by tetravalent Ce4+on the structural and magnetoresistive properties of La0.7−xCexCa0.3MnO3 polycrystalline manganites is presented. Samples with x=0, 0.1, 0.2 and 0.3 are prepared by solid state reaction method and characterized. For all doping levels, the X ray diffraction (XRD) analysis shows that the doping element is not completely soluble in the manganite. The cell parameters values, which decrease with Ce content, are refined in the orthorhombic system by taking into account the unreacted CeO2 phase. The observation by scanning electron microscopy (SEM) reveals a change in the morphology of the grains and the porosity of the samples by doping. The temperature dependence of magnetization curves shows a transition from paramagnetic to ferromagnetic state in all samples. A decrease of the Curie temperature Tc with doping is revealed. The resistivity of the samples increases with Ce content and shows a clear metal to insulator transition when measured as a function of temperature. The doping also decreases the temperature Tp of this transition, in accordance with the evolution of Tc values. The calculated magnetoresistance (MR) for a magnetic field of 5T increases gradually from 39.52% for x=0 to 66.18% for x=0.3.

Tuning magnetoresistive and magnetocaloric properties via grain boundaries engineering in granular manganites

The effect of interface size on the relative cooling power and magnetoresistive properties of La0.7Ba0.3MnO3 compounds is investigated.

Strain dependence of the physical properties of epitaxial La0.7Ca0.3MnO3 thin films grown on LaAlO3 substrates

We present a systematic study of the structural, magnetic, electrical and magnetoresistive properties of La0.7Ca0.3MnO3 thin films epitaxially grown on LaAlO3 single crystalline substrates using metal organic deposition process. The evolutions of the lattice parameters and the corresponding strain as a function of the film thickness (20–80 nm) have been investigated using X-ray diffraction measurements. The films were found to be totally relaxed for a thickness around 60 nm. Magnetization and resistance measurements as a function of temperature revealed a direct correlation of the transition temperature from a ferromagnetic state to the paramagnetic state with the film thickness. The temperature dependence of the resistivity (ρ (T)) has been fitted using various theoretical approaches. Below the transition temperature (TP) the ρ (T) graphs were well fitted using the ρ(T) = ρ0 + ATα formula, in which the fitting parameters ρ0 and α have been used to clarify the conduction mechanism. Above TP, the ρ (T) graphs were found to be well fitted using different models including the VRH model and the small polaron model. A magnetoresistance of 91% was measured at 248 K for the for 60 nm thick film under an applied magnetic field of 7 T. As well as a non-volatile resistive switching capacity of 15% on Ag contacts deposited on top of this film.

Structural and magnetic inhomogeneities, phase transitions, 55Mn nuclear magnetic resonance, and magnetoresistive properties of La0.6 − x Nd x Sr0.3Mn1.1O3-δ ceramics

The structure, lattice imperfection, and properties of ceramic samples La0.6 − x Nd x Sr0.3Mn1.1O3-δ (x = 0–0.4) have been investigated using the X-ray diffraction, resistive, magnetic (χac, 55Mn NMR), magnetoresistive and microscopic methods. It has been shown that there is a satisfactory agreement between the concentration decrease in the lattice parameters a of the rhombohedral (x = 0, 0.1, 0.2) and cubic (x = 0.3, 0.4) perovskite structures and the average ionic radii $$\bar R$$ for the lattice containing anion vacancies, cation vacancies, and nanostructured clusters with Mn2+ ions in A-positions. With an increase in the neodymium concentration x, the vacancy-type imperfection increases, the cluster-type imperfection decreases, the temperatures of metal-semiconductor phase transition T ms and ferromagnetic-paramagnetic phase transition T C decrease, and the content of the ferromagnetic phase decreases. The anomalous hysteresis is associated with the appearance of unidirectional exchange anisotropy induced in a clustered perovskite structure consisting of a ferromagnetic matrix and a planar antiferromagnetic cluster coherently coupled with it. An analysis of the asymmetrically broadened 55Mn NMR spectra has revealed a high-frequency electronic double exchange (Mn3+-O2−-Mn4+) ↔ (Mn4+-O2−-Mn3+) and an inhomogeneity of the magnetic and charge states of manganese due to the heterogeneous environment of the manganese ions by other ions and defects. The observed changes in the resonant frequency and width of the resonance curve are caused by changes in the ratio Mn3+/Mn4+ and magnetic inhomogeneity. An increase in the neodymium concentration x leads to a decrease in the ferromagnetic phase content determined from the dependences 4πNχac(T) and the 55Mn NMR curves. The phase diagram characterizes an interrelation between the composition, the imperfection of the structure, and the transport, magnetic, and magnetoresistive properties of lanthanum neodymium manganite perovskites. It has been found that there is a correlation between the imperfection, magnetic inhomogeneity, coercive force, and magnetoresistance effect exhibited by the perovskite structure.

Structural and magnetic inhomogeneities, phase transitions, 55Mn NMR, and magnetoresistive properties of La0.6Sr0.2Mn1.2 − x Nb x O3 ceramics

Ceramic samples of lanthanum strontium manganite perovskites La0.6Sr0.2Mn1.2 − xNbxO3 (x = 0–0.3) annealed at temperatures of 1260 and 1500°C have been investigated using the X-ray diffraction, electron microscopic, resistive, magnetoresistive, and magnetic (χac, 55Mn NMR) methods. It has been found that there is a correlation between the increasing unit cell parameter a of the rhombohedral R\(\bar 3\)c structure and the average ionic radius with increasing niobium concentration x and annealing temperature for the case where the lattice contains anion vacancies, cation vacancies, and nanostructured clusters. The observed increase in the electrical resistivity and decrease in the temperatures of metal-semiconductor phase transition Tms and ferromagnetic-paramagnetic phase transition TC with an increase in the niobium concentration x and the annealing temperature have been explained by the decrease in the content of the ferromagnetic phase, as well as by changes in the ratio Mn3+/Mn4+, the oxygen nonstoichiometry, and the concentration of defects weakening the high-frequency electronic exchange of the ions Mn3+ ↔ Mn4+. The presence of nanostructured clusters in the lattice has been confirmed by an anomalous hysteresis associated with the unidirectional exchange anisotropy of the interaction between the ferromagnetic matrix and antiferromagnetic clusters with Mn2+ and Nb3+ in distorted A-positions. An analysis of the asymmetrically broadened 55Mn NMR spectra and their computer decomposition have revealed a high-frequency electronic exchange and an inhomogeneity of the magnetic and valence states of manganese due to the nonuniform distribution of all ions and defects. Two types of magnetoresistive effects have been found: one effect, which is observed near the phase transition temperatures TC and Tms, is caused by scattering at intracrystalline nanostructured heterogeneities of the imperfect perovskite structure, and the other effect, which is observed in the low-temperature range, is induced by tunneling through intercrystalline mesostructured boundaries. The phase diagram has demonstrated that there is a strong correlation between the composition, structure, resistive and magnetic properties of rare-earth manganites.

Magnetotransport Properties of La<sub>0.6</sub>Sr<sub>0.2</sub>Mn<sub>1.2</sub>O<sub>3</sub> Films: Effects of Film Thickness and Substrate-Induced Strain

Electric and magnetoresistive properties of La0.6Sr0.2Mn1.2O3 films deposited on SrTiO3 (001) and LaAlO3 (001) single crystalline substrates by magnetron sputtering have been studied. Characteristic features of the evolution of resistivity, magnetoresistance and Curie temperature upon the decrease of film thickness from 500 to 2 nm are specified. A key role of a thin strained layer adjacent to the substrate is demonstrated. The critical thicknesses of the strained layer are calculated for the films deposited on different substrates

Structural and magnetic inhomogeneity, phase transitions, magnetoresonance and magnetoresistive properties of La0.6 − x Pr x Sr0.3Mn1.1O3 (x = 0–0.6)

Ceramic samples of manganite perovskites La0.6 − xPrxSr0.3Mn1.1O3 (x = 0−0.6) have been studied using the X-ray diffraction, resistive, magnetic (χac, 55Mn NMR), microscopic, and magnetoresistive methods. It has been found that an increase in the praseodymium concentration x leads to a transition from the rhombohedral R\(\bar 3\)c (x = 0–0.3) to orthorhombic Pbnm (x = 0.4–0.6) perovskite structure. It has been shown that the real perovskite structure contains anion and cation vacancies, whose concentrations increase with an increase in the praseodymium concentration x. A decrease in the metal-insulator phase transition temperature Tmi and the ferromagnetic-paramagnetic phase transition temperature Tc with increasing x correlates with an increase in the concentration of vacancies weakening the high-frequency electronic exchange Mn3+ ↔ Mn4+. For compositions with x = 0 and 0.1, when the lattice contains not only vacancies but also nanostructured clusters with Mn2+ in the A-positions, there is an anomalous hysteresis. An analysis of the asymmetrically broadened 55Mn NMR spectra of the compounds has revealed a high-frequency electronic exchange of the ions Mn3+ Mn4+ in the B-positions and a local heterogeneity of their surrounding by other ions (La2+, Pr3+, Sr2+) and vacancies. The phase diagram has demonstrated that there is a strong correlation between the composition, imperfection of the perovskite structure, phase transition temperatures Tmi and Tc, and magnetoresistive properties.

Structural and magnetic heterogeneities, phase transitions, 55Mn NMR, and magnetoresistive properties of La0.6Sr0.3 − x Bi x Mn1.1O3

The structural, resistive, magnetic, and magnetoresistive properties of the La0.6Sr0.3 − xBixMn1.1O3 ceramics have been studied. The substitution of Bi ions for Sr ions increases the lattice parameter of the rhombohedral perovskite structure, decreases the metal-semiconductor and ferromagnet-paramagnet phase transition temperatures and the peak of the magnetoresistive effect, and increases the resistivity, approaching the system to the ferroelectric state. The 55Mn NVR study indicates on the high-frequency Mn3+ ↔ Mn4+ superexchange and heterogeneity of the valence and magnetic states of manganese due to the nonuniformity of distribution of all ions and defects. The phase diagram has been constructed, which shows a strong correlation between the structural, magnetic, and magnetoresistive properties.

Study of structural, transport and magneto-resistive properties of La0.7Ca0.3−xCexMnO3 (0≤x≤0.2)

Abstract We have synthesized a series of La0.7(Ca0.3−xCex)MnO3 (0≤x≤0.2) by standard solid-state reaction method. X-ray diffraction (XRD) measurement was carried out for structural studies and Rietveld refinement was done for structural analysis. The transport properties were studied using four probe technique. The temperature dependence of the resistivity was measured in the temperature range of 20 K to room temperature. It is found that all samples show a systematic variation in metal to insulator transition at transition temperature (TP) and resistivity (ρ) with the relative concentration of hole and electron doping in the system. The samples showed varying amounts of colossal magnetoresistance depending upon temperature and applied magnetic field. The magnetoresistance values as high as 72% were observed in x=0 sample.

Influence of cobalt on the structural and magnetic Inhomogeneities, phase transitions, and magnetoresistive properties of La0.6Sr0.2Mn1.2 − x Co x O3 ± δ

The structure and properties of magnetoresistive ceramics La0.6Sr0.2Mn1.2 − x Co x O3 ± δ (x = 0−0.3) sintered at a temperature of 1200°C are investigated using x-ray diffraction, resistance, and magnetic (χ ac , M, 55Mn NMR) measurements. It is shown that the samples contain the rhombohedral (R $$ \bar 3 $$ c) perovskite (90%) and tetragonal (I41/amd) hausmannite (10%) phases. The lattice parameters of these phases decrease with an increase in the cobalt content x. The real perovskite structure involves point defects (anion and cation vacancies) and nanostructured defects of the cluster type. An analysis of the asymmetrically broadened 55Mn NMR spectra confirms the high-frequency electron-hole exchange between Mn3+ and Mn4+ ions and a local inhomogeneity of their environment by other ions and defects of the point and cluster types. An increase in the Co content leads to an increase in the electrical resistivity, an enhancement of the magnetoresistance (MR) effect, and a decrease in the magnetic susceptibility and the temperatures of the metal-semiconductor (T ms ) and ferromagnetic-paramagnetic (T C) phase transitions due to the suppression of the exchange interaction between Mn3+ and Mn4+ ions by vacancies and clusters. The introduction of cobalt results in a decrease in the ferromagnetic component and the activation energy. The magnetoresistance effect in the vicinity of the phase transition temperatures T ms and T C is associated with the scattering of charge carriers from intracrystallite inhomogeneities of the lattice, and the low-temperature magnetoresistance effect is governed by the tunneling at the intercrystalline boundaries.

Magnetic and magnetoresistive properties of La0.65−xEuxSr0.35MnO3

Abstract Eu-doped perovskites La 0.65− x Eu x Sr 0.35 MnO 3 (0.05 ≤ x ≤ 0.30) were synthesized by sol–gel method using citric acid and characterized by X-ray diffraction, magnetization, resistivity and magnetoresistance (MR) experiments. All samples had a single hexagonal perovskite structure. As x increased from 0.05 to 0.30, the Curie temperature T C for the samples decreased from 352 to 242 K. It was found that two transition points appeared when the resistivity changed with increasing temperature, and upon an application of a magnetic field of 20 kOe the maximum magnetoresistivity of 18% for the La 0.65− x Eu x Sr 0.35 MnO 3 with x = 0.20 was obtained at room temperature 300 K. The mechanism of the transitions for the samples was explored.

Effect of processing conditions on the phase transformations, structure and magnetoresistive properties of La0.7Sr0.3MnO3±γ manganites

Effect of processing conditions on the phase transformations, structure and magnetoresistive properties of La0.7Sr0.3MnO3±γ manganites

Changes of the local distortions and colossal magnetoresistive properties of La0.7Ca0.3MnO3 induced by Ti or Ga deffects

The magnetoresistive properties of La0.7Ca0.3MnO3 change rapidly when Ti or Ga is substituted on the Mn site for concentrations, x, from 1 to 10%. The samples exhibit colossal magnetoresistance (CMR) and the resistivity increases dramatically with dopant concentration. The temperature of the resistivity peak, TR , shifts rapidly to lower temperatures with increasing x, and the ferromagnetic transition broadens. However, the transition temperature, Tc is only slightly suppressed. Consequently TR occurs well below Tc for x above 2%. Investigations of these materials using Mn XAFS show that changes in the local structure, parameterized by the pair-distribution width, σ, correlate with Tc and the sample magnetization. For a given dopant, the resistivity peak occurs when [sgrave]2 decreases below a critical value. Both dopants produce extended defects which increases the resistivity of the nearby material considerably. The data suggest that even at ∼4% most of the sites are slightly distorted at low T.

Structural and magnetoresistive properties of La0.7Ca0.3Mn0.96(Al1−xInx)0.04O3

Structural, magnetic, and transport properties of ABO3-type La0.7Ca0.3Mn0.96(Al1−xInx)0.04O3 are investigated. Different structure deformation from that in the A-site doping, characterized by the synchronous variation of the lattice constants b with c/√ versus the content of In in the compounds, is observed. The metal–semiconductor transition shows a strong In content dependence. The transition temperature decreases monotonously from 180.7 to 103.4 K as x varies from 0 to 1, with a corresponding maximum resistivity ranging from 2.9 to 410.8 Ω cm. The magnetoresistive properties of the materials are strongly affected by the size mismatch between A- and B-site ions, and a relation similar to that presented by Hwang et al. [Phys. Rev. Lett. 75, 914 (1995)] is observed though controlling of the tolerance factor, is realized by B-site doping.

Effect of crystallinity on the magnetoresistive properties of La0.8MnO3−δ thin films grown by chemical vapor deposition

We report here a study on the role of crystallinity on the magnetoresistive properties of self-doped La0.8MnO3−δ thin films. Films have been grown by a liquid-source metalorganic chemical vapor deposition technique on two different single crystals: SrTiO3 (001) and Al2O3 (012). Epitaxial films are obtained on strontium titanate and show a high magnetoresistance peak at low fields: maximum magnetoresistive effect in the vicinity of the magnetic transition temperature, and negligible 50 K below. Polycrystalline films are observed on sapphire; they exhibit a lower magnetoresistance of several percent which remains nearly constant over a wide temperature range. Two magnetoresistive regimes can be distinguished in these films: in low fields (up to 5 mT), a strong magnetoresistance is obtained with a sensitivity of 0.28%/mT at 78 K; in higher fields, the magnetoresistance is linear and lower than this obtained in epitaxial films. The role of grain boundaries on the magnetoresistive effect is discussed.