MnO3 Nanocrystalline Research Articles

Evolution of ferromagnetic cluster in perovskite La0.88Sr0.12MnO3 nanocrystalline detected by EPR spectrum

Electron paramagnetic resonance (EPR) studies were performed on La0.88Sr0.12MnO3 (LSMO) nanocrystalline together with the measurement of its magnetization. Various spectrum parameters including line width, effective g-value and double-integrated intensities have been analyzed in detail. We found nonlinear behavior occurred in the inverse susceptibility far above the Curie temperature TC, indicating short-range ferromagnetic (FM) clusters and Griffiths-like phase behavior in the paramagnetic (PM) phase. Based on the variation of EPR spectra, except for a typical PM resonance peak, an extra resonance signal was observed in the lower field region and developed as temperature decreased from 320 K to 110 K, which gave a direct evidence of the existence of FM cluster in the PM region of LSMO nanocrystalline. We proposed that the appearance of the Griffiths phase was due to the short FM correlation in the PM regime enhanced by surface spin ordering.

Impact of Crystallite Size on Structural, Optical and Magnetic Characteristics of La0.7Sr0.15Ca0.15MnO3 Nanocrystalline

Nanocrystalline La0.7Sr0.15Ca0.15MnO3 (LSCMO) manganites were prepared by the combustion process and heated to various annealing temperatures (TA) to get various sized crystallites. The X-ray diffraction (XRD) patterns provided evidence that a Rhombohedral structure with space group was formed. Additionally, an increase in the size of the crystallites was observed, from 15.64 to 36.78nm, as the temperature (TA) increased from 700℃ to 1300℃. The FESEM micrographs revealed that homogeneous with porosity. The FTIR spectra showed five absorption peaks. The Optical energy gap of LSCMO nanocrystalline is decreased from 3.51 to 3.28 eV as annealed temperature raised, reveals that the LSCMO nanoparticles are semiconductor in nature. Room temperature Raman spectra of LSCMO nanoparticles demonstrate a notable reliance on annealing temperature. When the Raman modes were analysed with respect to TA, it was observed that the Raman vibrational phonon mode below 200cm-1 (A1g) and four modes (Eg) in the range 200-800cm-1 displayed significant displacements and widening, which were associated with oxygen sublattice distortion. Considerable changes were observed in both the intensity and full width half maximum (FWHM) of the five Raman modes as the annealing temperature increased. Magnetic behaviour using M-H loop at room temperature were measured by the Vibrating sample magnetometer revealed that gradation of saturation magnetization as the function of annealing temperature. Hence there is a remarkable crystallite size effect on optical and magnetic properties of LSCMO nanocrystallites.

Microwave absorbing properties of La1-x Ba x MnO3 (x=0.1,0.2,0.3,0.4,0.5) nano-particles

Electromagnetic wave absorbing materials have always been a research hotspot in military and civil fields. La1-x Ba x MnO3 nanocrystalline powders were prepared by sol-gel method. XRD analysis shows that La1-x Ba x MnO3 is a single perovskite structure, and the lattice constant changes with the doping amount. SEM analysis shows that La1-x Ba x MnO3 is basically spherical with an average particle size of about 80 nm. The relationship between the complex permittivity and permeability with microwave frequency was measured by microwave vector network analyzer. According to the measured data, the microwave reflectivity and loss factor of the sample were calculated, and the microwave loss mechanism of the sample was discussed. The results show that x has a great influence on the absorbing properties of La1-x Ba x MnO3. When x is 0.2 and the thickness is 1.6mm, the absorption bandwidth above 10dB reaches 2.1GHz and the maximum absorption value is 25dB. The microwave loss of La1-x Ba x MnO3 mainly comes from the dielectric polarization loss of perovskite materials, it also comes from conductivity loss, magnetic loss and interface polarization loss due to Ba doping and nano effect.

Strong correlation between flux pinning and epitaxial strain in the GdBa2Cu3O7-x /La0.7Sr0.3MnO3 nanocrystalline heterostructure.

The effect of magnetic flux pinning is investigated in GdBa2Cu3O7 (GdBCO) thin films with two different types of ferromagnetic La0.7Sr0.3MnO3 (LSMO) buffers (nanoparticles and a layer) deposited on an STO substrate. Magnetization analyses reveal the presence of multiple flux pinning mechanisms responsible for the improvement in the critical current density of GdBCO films. While core pinning becomes a dominant pinning mechanism in GdBCO films with LSMO nanoparticles, a hybrid effect of magnetic-volume and core-point pinning is observed in GdBCO films with LSMO layers. Examinations of local structures for both LSMO and GdBCO using extended X-ray absorption fine structure spectroscopy (EXAFS) exhibit a close relation between the parameters in the pinning force scaling and the length ratio of the Mn–O bond to the Cu–O bond. This result implies that the origin of core pinning is probably attributed to epitaxial strain induced by lattice mismatch between LSMO and GdBCO. Therefore, an appropriate strain state of LSMO is required for an effective operation of magnetic pinning.

Structural characterization, magnetic, magnetocaloric properties and critical behavior in lacunar La0.5Eu0.2Ba0.2□0.1MnO3 nanoparticles

The lacunar La0.5Eu0.2Ba0.2□0.1MnO3 nanoparticles where □ is a barium deficiency has been prepared using the sol-gel method. The M-T data suggests that the sample undergoes a paramagnetic (PM) to ferromagnetic (FM) transition upon cooling. Deviation of the temperature dependence of inverse susceptibility curves from the Curie Weiss law and less than unity susceptibility exponents indicating the existence of a Griffiths singularity. The magnetocaloric effect and the critical behavior of the sample are systematically studied using bulk magnetization M (H, T) in the vicinity of the Curie temperature. The critical exponents have been obtained using different methods such as modified Arrott plot, critical isotherm analysis and field dependence of magnetocaloric effect. Though the self-consistency and reliability of obtained critical exponents of β = 0.581 ± 0.022, γ = 0.165 ± 0.008 and δ = 3.12 ± 0.03 are verified by the Widom scaling law and scaling equations, the critical parameters do not obey magnetocaloric effect scaling laws, indicating that the nanometer size effect play a significant role on the magnetic phase transition for La0.5Eu0.2Ba0.2□0.1MnO3 nanocrystalline.

Evidence of emerging Griffiths singularity in La0.5 Sr0.5 MnO3 nanocrystalline probed by magnetization and electron paramagnetic resonance

We present an investigation of Griffiths singularity in La0.5 Sr0.5 MnO3 nanocrystalline by means of magnetic susceptibility and electron paramagnetic resonance (EPR). An unusual platform was found in paramagnetic region. Based on the analysis of EPR spectrum and magnetization variation across the whole temperature range of phase transition, we confirm it is due to the presence of Griffiths singularity rather than a superparamagnetic state in the nanocrystalline system. Such a singularity phase is constituted with some correlated ferromagnetic clusters which embed in paramagnetic matrix. Although they form ferromagnetic spin correlation, the system do not yield any spontaneous magnetization. According to core–shell model, the emergence of Griffiths singularity can be considered due to the presence of local ferromagnetic fluctuations originated from surface spin disorder as the sample size is confined to nanoscale.

Grain size-induced structural, magnetic and magnetoresistance properties of Nd0.67Ca0.33MnO3 nanocrystalline thin films

The effects of grain size (G S) on the structural, magnetic and magnetoresistance properties of sol–gel-derived Nd0.67Ca0.33MnO3 (NCMO) nanocrystalline thin films were investigated. To change the G S of the NCMO samples, the annealing temperature (T A) was changed from 600 to 800 °C. All the prepared samples were confirmed as hexagonal single-phased polycrystalline structure. The average nanocrystalline size and G S were increased with increasing T A. The range of the G S was approximately 25–40, 50–65 and 75–90 nm for the NCMO samples annealed at T A = 600, 700 and 800 °C, respectively. As the G S increased, the metal–insulator transition temperature, T MI, and the paramagnetic–ferromagnetic transition temperature, T C, also increased including the ferromagnetic response. The magnetoresistance, MR, values were found to increase with increasing the G S at any annealing temperature.

Emergence of low dimensional ferroelectricity in Pr0.67Ca0.33MnO3 nanocrystal arrays

We discuss the emergence of low dimensional ferroelectricity in self-organized Pr0.67Ca0.33MnO3 nanocrystalline arrays deposited on a Si substrate.

Enhancement of refrigeration capacity and table-like magnetocaloric effect in La0.8Ca0.2MnO3/La0.8K0.2MnO3 nanocrystalline composite

In this paper we report on the magnetocaloric effect and refrigeration capacity (RC) of La0.8Ca0.2MnO3(LCMO)/La0.8K0.2MnO3(LKMO) composite with a mass fraction of 1:1. X-ray diffraction patterns indicate that the component manganites crystalize in the same rhombohedral structure. The LCMO and LKMO undergo second-order phase transitions at 247K and 281K, respectively. The maximum values of isothermal entropy change (−ΔST,max) are found to be 4.25J/kgK and 3.71J/kgK under a magnetic field change of 5T for LCMO and LKMO, respectively. The composite exhibits a table-like ΔST curve with slightly lowered peak value. An enhancement of 33%–35% for RC has been found in the composite when comparing with those of the components. It reveals that the combination of magnetocaloric materials with different Curie temperatures is a possible method for improving RC.

Investigation of Magnetic Entropy Change and Griffiths-like Phase in La0.65Ca0.35MnO3 Nanocrystalline

In this paper, we reported a detailed study of magnetic properties and magnetic entropy change of La 0.65Ca0.35MnO3 nanocrystalline, which was prepared by using the sol–gel method. The structural analysis shows that the nanocrystalline sample crystalizes in orthorhombic perovskite structure and the average size is about 30 nm. Based on the measurements of magnetization, a larger effective magnetic moment was obtained and an obvious deviation of the inverse magnetic susceptibility was observed, indicating the presence of Griffiths-like phase in paramagnetic region. Around the temperature of paramagnetic–ferromagnetic phase transition, the magnetocaloric effect (as represented by the magnetic entropy change) was determined from isothermal magnetization and calculated with Maxwell relation. Compared with bulk polycrystalline, the obtained magnetic entropy change in nanocrystalline is small. This result clearly reveals that the decrease of the sample’s size to nanoscale is detrimental for the increase of magnetocaloric effect of magnetic materials. Besides the particle size and surface effect, the paramagnetic–ferromagnetic phase transition driven from first to second order should be a main reason for the small magnetocaloric effect in La 0.65Ca0.35MnO3 nanocrystalline.

Transport properties and microstructure of La0.7Sr0.3MnO3 nanocrystalline thin films grown by polymer-assisted chemical solution deposition

Perovskite-based materials can be widely used in the aerospace and transportation field. Perovskite manganese oxides La0.7Sr0.3MnO3 (LSMO) thin films were grown on LaAlO3 (100) and Si (100) single crystal substrates by the polymer-assisted chemical solution deposition (PACSD) method. Electronic transport behavior, microstructure, and magnetoresistance (MR) of LSMO thin films on different substrates were investigated. The resistance of LSMO films fabricated on LaAlO3 substrates is smaller than that on the Si substrates. The magnetic field reduces resistance of LSMO films both on Si and LAO in the wide temperature region, when the insulator-metal transition temperature shifts to higher temperature. The low-field magnetoresistance of LSMO films on Si in low temperature range at 1 T is larger than that of LSMO films on LAO. However, the MR of LSMO film on LAO films at room-temperature is about 5.17 %. The thin films are smooth and dense with uniform nanocrystal size grain. These results demonstrate that PACSD is an effective technique for producing high quality LSMO films, which is significant to improve the magnetic properties and the application of automotive sensor.

Magnetic and transport properties of chemical solution deposited (100)-textured La0.7Sr0.3MnO3 and La0.7Ca0.3MnO3 nanocrystalline thin films

A study of the magnetic and electrical properties of (100)-oriented La0.7(Sr,Ca)0.3MnO3 thin films prepared by an optimized chemical solution deposition process on a (100) SrTiO3 single-crystal substrate is reported in this paper. The films were studied by high-resolution scanning electron microscopy, x-ray diffraction, vibrating sample magnetometer, ferromagnetic resonance and four-point-probe electrical measurements. A characteristic nanocrystalline texture with ∼15 nm crystallites is observed in both films. Remarkably, the resistivities of these films are three orders of magnitude smaller compared with unoptimized films grown even on the same substrate. The magnetotransport properties were determined as a function of temperature and applied field magnitude, and compared with bulk crystals and vacuum-deposited single crystalline (epitaxial) thin films as well as manganite nanostructures reported in the literature. Both films display large values of colossal magnetoresistance at around room temperature. Significantly, the magnetoresistance in (100) La0.7Sr0.3MnO3 thin film is observed to be highly linear even at low fields near the metal–insulator transition temperature. However, the dependence of these promising properties on the nanocrystal size remains to be explored.

Influence of polymerizing agent on structure and spectroscopic properties of nano‐crystalline La0.8Sr0.2MnO3 powders

AbstractStrontium‐doped lanthanum manganite (La1‐xSrxMnO3 or LSM) is the material most widely used on solid oxide fuel cells cathode. In this work, nano‐scale La0.8Sr0.2MnO3 powders have been synthesized by polymeric precursor‐based methods using different polymerizing agents with the aim of evaluating the influence of this change in the final powder. The powders calcined at 700 °C for 2 h have been characterized by X‐ray diffraction (XRD), scanning electron microscopy (FE‐SEM) and Fourier transform infrared spectroscopy (FTIR) in order to investigate the quality of both synthesis routes. It is shown that the crystal structure and morphology of the particles are significantly dependent on the preparation conditions. Single phase and La0.8Sr0.2MnO3 nano‐crystalline particles less than 30 nm were obtained using ethylene glycol as polymerizing agent. FTIR results have been indicated that only the powder obtained using gelatin presented small traces of hydroxyl groups on its surface. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Magnetotransport and magnetoelastic effects in Co-doped La0.7Sr0.3MnO3 nanocrystalline perovskites

La 0.7 Sr 0.3 Mn 1− x Co x O 3 ( x =0, 0.05, 0.1) nanoparticles, prepared by sol–gel method, were studied by means of X-ray diffraction, transmission electron microscopy , resistivity , magnetoresistance , thermal expansion and magnetostriction measurements. Results show that partial substitution of Mn by Co leads to a reduction in lattice parameters , enhancement of resistivity and room temperature magnetoresistance MR, decrease of metal-insulator transition temperature T MI and T C , an increase in thermal expansion coefficient, volume magnetostriction and anisotropic magnetostriction. The latter increases about one order of magnitude with 10% Co substitution. In comparison with Mn ions, the Co ions possess higher anisotropy energy, larger magnetostriction effect, smaller ionic size and spin state transitions with increase in temperature and magnetic field; this suggests that Co substitution leads to double-exchange interaction weakening, resulting in suppression of ferromagnetic long-range order and metallic state and increase of magnetic anisotropy . Furthermore, our samples have a relatively lower T MI and T C , higher resistivity and MR, compared with the reported values for similar compounds with larger particle sizes. This is attributed to the nanometric grain size and spin-polarized tunneling between neighboring grains.

Suppression of charge order and exchange bias effect in Nd0.5Ca0.5MnO3 nanocrystalline

An Nd0.5Ca0.5MnO3 (NCMO) sample (average diameter ∼45 nm) is synthesized by the sol–gel method. The temperature dependence of magnetization indicates that the charge order state is suppressed and a ferromagnetic (FM) transition occurs at ∼100 K. In addition, the magnetic hysteresis loop at 10 K under a cooling field of 10 kOe shifts to both the horizontal and the vertical directions when the measure field is 10 kOe. With an increase in the measure field, both the horizontal and the vertical shifts decrease. When the measure field is 50 kOe, the vertical shift vanishes but the horizontal shift still exists. The observed exchange bias effect is attributed to the exchange coupling between the antiferromagnetic core and the FM shell which embodies spin glass-like surface layers.

Chemical synthesis and magnetic properties of nanocrystalline (La0.67−X Gd X )Sr0.33MnO3 using amorphous molecular alloy as precursors

A new route to synthesize nanosized crystalline of (La0.67−XGdX)Sr0.33MnO3 (X=0.05, 0.10, 0.15, 0.20) perovskite-type complex oxides at calcination temperature of 600–1000 °C using the amorphous molecular alloy as precursors was reported. The precursor could be completely decomposed into complex oxide at temperature below 500 °C according to the TGA and DTA results. XRD demonstrates that the decomposed species is composed of perovskite-type structure at calcination temperature of 600 °C for 2 h. The particle size that depends on the calcination temperature of the precursor is in a range of 30–120 nm as determined by transmission electron microscopy (TEM). This method is effective and can be easily quantitatively controlled to synthesize nanosized perovskite-type complex oxides. The magnetic properties of (La0.67−XGdX)Sr0.33MnO3 nanocrystalline were preliminary studied.