MnO3 System Research Articles

Structural, magnetic, and transport properties in a Cu-doped La0.7Ca0.3MnO3 system

The structural, magnetic, and transport properties of La0.7Ca0.3Mn1−xCuxO3 (0⩽x⩽0.2) have been investigated. The maximum magnetoresistance (MR) is about 4×106% for the sample with x=0.15, which is about ∼104 times the maximum MR for samples with x⩽0.1. A change in the structural parameters and magnetic and resistivity properties of the samples shows that Cu exists in Cu3+ ionic form in the sample with x⩽0.05. However, Cu2+ ions begin to appear and then they increase with further Cu doping.

Evolution of Magnetotransport Properties and Spin-Glass Behavior of the La0.7-xNdxPb0.3MnO3 System

The effect of neodymium substitution on the lanthanum site in La0.7-xNdxPb0.3MnO3 perovskite polycrystalline has been systematically studied. The substitution of neodymium for lanthanum causes structure change from rhombohedral to orthorhombic. Ferromagnetism is suppressed as neodymium content increases. The magnetic order changes from a ferromagnetic long-range order with x=0.0 to a spin-glass nature with x=0.7. Besides, the ferromagnetic-paramagnetic transition temperature values are lower for the neodymium phases than for the lanthanum ones. Therefore, the introduction of neodymium degrades symmetry of the structure, diminishes the spin-coupling exchange interaction, and results in changes of magnetic properties. This fact is in good agreement with increasing the B value in Bloch's T3/2 law and decreasing the spin-wave stiffness parameter D in quadratic dispersion relation.

XAS and MCD studies in Eu0.6Sr0.4MnO3.

Eu(1-x)Sr(x)MnO3 system is one of the perovskite manganites that exhibit the giant magneto resistance effect and the transition from the insulator phase to the metal. Eu(0.6)Sr(0.4)MnO3 behaves as a ferromagnetic semiconductor and has an Insulator-Metal (IM) transition induced by external magnetic field, which could be found only in this system among the perovskite manganites group. The mechanism of the transition was investigated by X-ray Magnetic Circular Dichroism (XMCD) at the Mn L2,3-edges of and the Eu M4,5-edges in Eu(0.6)Sr(0.4)MnO3.

Studies on Crystal Structure and Magnetic Scaling Behavior of Perovskite-Like (La1−xPbx)MnO3 System with x = 0 - 0.5

ABSTRACTThe magnetic critical behaviors in the perovskite-like (La1−xPbx)MnO3 series with x = 0.0 ∼ 0.5 are studied by means of dc magnetic measurements. All the samples crystallize in the rhombohedral unit cell with a C R 3 space group (a 0.54 nm and c 1.33 nm). The detailed crystallographic parameters of all the samples are obtained by the refinements of the powder x-ray diffraction data using the Rietveld method. The substitution effect of Pb2+ ions on La3+ sites induces a mixed-valence state of Mn3+/Mn4+ and enhances magnetic transition temperature in the (La1−xPbx)MnO3 system. The transition temperature TC increases with the Pb content from 225 K as x = 0 to 355 K as x = 0.5. The canonical spin-glass behaviors in low fields and the scaling behaviors of magnetic physical quantities are clearly observed in all our samples. The values of the related critical exponents and the scaling functions of magnetic data are close to those of the conventional spin glass systems.

Hyperfine Fields at the Cd Site in La0.67Cd0.25MnO3 CMR Manganites

Although Cd and Ca ions have the same valence and cation size, their incorporation into vacancy-doped La manganites induce different properties. While the incorporation of Ca leads to high Tc up to 250 K and induces a metallic-like behaviour, the incorporation of Cd severely reduces Tc and promotes insulator-like behaviour. In this work, the Cd hyperfine fields have been measured with the Perturbed Angular Correlations (PAC) technique after implantation and annealing of 111mCd in La–Cd–MnO3 samples. The PAC results are compared with measurements of the resistivity and magnetization performed on the same samples. The mixed La and Mn site Cd occupancy is suggested as a possibility to explain the properties of the La–Cd–MnO3 system.

A large low field colossal magnetoresistance in the La0.7Sr0.3MnO3 and CoFe2O4 combined system

La 0.7 Sr 0.3 MnO 3 and CoFe2O4 samples have been prepared by a sol-gel process. A mixture of the two samples was annealed at 800 °C and the scanning electron micrograph shows large CoFe2O4 grains well surrounded by La0.7Sr0.3MnO3 grains. The powder x-ray diffraction patterns indicate no evidence of reaction between the La0.7Sr0.3MnO3 and CoFe2O4. The resistivity of the combined sample (with 20 wt% CoFe2O4) is about an order of magnitude larger than that of the same-grain-sized La0.7Sr0.3MnO3 sample, while a large low field magnetoresistance (MR) has been obtained in the combined samples. Under an applied field of 5 kOe, the MR of the combined sample is 10% even at 280 K and 5% at 290 K, whereas the same nanosized La0.7Sr0.3MnO3 sample is only 2% and 1%, respectively.

Finite Ferromagnetic Clusters La1−xZnxMnO3 (x = 0.05 and 0.10)

Detailed magnetic and nonlinear susceptibility measurements of the La1−xZn x MnO3 system are reported. For x = 0.05 and 0.1, a typical ferromagnetic (FM) signal in the field-cooled curve is observed at 38 K. However, for the insulating antiferromagnetic (AFM) parent compound LaMnO3 and for the x = 0.2 and 0.33 samples, the magnetization curves in the low temperature range, are smooth and flat. This observation confirms the coexistence of finite FM clusters in the insulating AFM region below the critical concentration (x c = 0.16) for percolation, predicted by the percolation model.

Room Temperature Magnetoresistance at Low Magnetic Fields in La 0.7 Ba 0.3 MnO 3

This paper examines the possibility of enhancing the room temperature magnetoresistance at low applied magnetic fields in single layer La0.7 Ba0.3 MnO3 thin films. The influence of lattice mismatch strain, as well as the effect of different frequency regimes, on the magnetoresistance is explored. The effects of lattice mismatch strain are studied by measuring the magnetoresistance as a function of the La0.7 Ba0.3 MnO3 film thickness, oxygen annealing, and lattice matched buffer layers. We find that the release of the lattice mismatch strain improves the magnetoresistance at room temperature and at low magnetic fields. In fact, the highest magnetoresistance at room temperature (−1.7% at 500 Oe) has been found for the 1600 A as-grown La0.7 Ba0.3 MnO3 film, whereas the largest magnetoresistance (−1.9% at 500 Oe) is found at 309 K for the 1000 A La0.7 Ba0.3 MnO3 film annealed in flowing O2 for 1 h at 900°C. Finally, we find that the microwave magnetoresistance is the same as the dc magnetoresistance when the cavity corrections are applied. In the single layer La0.7 Ba0.3 MnO3 system, the low field magnetoresistance at room temperature is far from being technologically viable.

Transport and magnetic properties of laser ablated La0.7Ce0.3MnO3 films on LaAlO3

La 0.7 Ce 0.3 MnO 3 is a relatively new addition to the family of colossal magnetoresistive manganites, in which the cerium ion is believed to be in the Ce4+ state. In this article, we report the magnetotransport properties of laser ablated La0.7Ce0.3MnO3 films on LaAlO3, and the effect of varying the ambient oxygen pressure during growth and the film thickness. We observe that the transport and magnetic properties of the film depend on the oxygen pressure, surface morphology, film thickness, and epitaxial strain. The films were characterized by x-ray diffraction using a four-circle goniometer. We observe an increase in the metal-insulator transition temperature with decreasing oxygen pressure. This is in direct contrast to the oxygen pressure dependence of La0.7Ca0.3MnO3 films and suggests the electron doped nature of the La0.7Ce0.3MnO3 system. With decreasing film thickness we observe an increase in the metal-insulator transition temperature. This is associated with a compression of the unit cell in the a-b plane due to epitaxial strain. On codoping with 50% Ca at the Ce site, the system (La0.7Ca0.15Ce0.15MnO3) is driven into an insulating state suggesting that the electrons generated by Ce4+ are compensated by the holes generated by Ca2+, thus making the average valence at the rare-earth site 3+ as in the parent material LaMnO3.

Percolative phase separation underlies colossal magnetoresistance in mixed-valent manganites

Colossal magnetoresistance1—an unusually large change of resistivity observed in certain materials following application of magnetic field—has been extensively researched in ferromagnetic perovskite manganites. But it remains unclear why the magnetoresistive response increases dramatically when the Curie temperature (T C) is reduced. In these materials, T C varies sensitively with changing chemical pressure; this can be achieved by introducing trivalent rare-earth ions of differing size into the perovskite structure2,3,4, without affecting the valency of the Mn ions. The chemical pressure modifies local structural parameters such as the Mn–O bond distance and Mn–O–Mn bond angle, which directly influence the case of electron hopping between Mn ions (that is, the electronic bandwidth). But these effects cannot satisfactorily explain the dependence of magnetoresistance on T C. Here we demonstrate, using electron microscopy data, that the prototypical (La,Pr,Ca)MnO3 system is electronically phase-separated into a sub-micrometre-scale mixture of insulating regions (with a particular type of charge-ordering) and metallic, ferromagnetic domains. We find that the colossal magnetoresistive effect in low-T C systems can be explained by percolative transport through the ferromagnetic domains; this depends sensitively on the relative spin orientation of adjacent ferromagnetic domains which can be controlled by applied magnetic fields.

Spatial cross-over of polarons across the CMR transition in La0.75Ca0.25MnO3 system.

Spatial cross-over of polarons across the CMR transition in La0.75Ca0.25MnO3 system.

Substrate, annealing, and Mn excess effects on La–Ca–MnO3 thin films grown by metalorganic chemical vapor deposition: A way to room-temperature Tc

Oriented thin films of the La–Ca–MnO3 system with several Mn-excess compositions were prepared by aerosol-assisted metalorganic chemical vapor deposition. Depositions both on MgO (100) and LaAlO3 (100) substrates were performed at temperatures between 700 and 800 °C, with 30 min in situ oxygen annealing at the deposition temperature. The films deposited on LaAlO3 have much better structural quality with rocking curves of 0.3–0.7 full width at half maximum and higher Tc. For films with Mn excess, an ex situ annealing (800 °C for 1 h in flowing oxygen) increases Tc dramatically, from 180–190 K to values in the range 240–296 K, above the maximum Tc of the stoichiometric, optimally doped La0.67Ca0.33MnO3 composition. This behavior may be associated with the presence of La vacancies, which act as self-dopants, and whose role is enhanced after suitable annealing. The films present high magnetoresistance values in the vicinity of the critical temperatures: at 7 kOe, 32% for a film with Tc=279 K and 13% for a film with Tc=296 K. The magnetic properties of the films on MgO were degraded by annealing, probably due to Mg diffusion to the film.

Is Magnetic Circular Dichroism Surface Sensitive in the Manganese Perovskites?

AbstractWe compare the magnetization versus temperature, determined by magnetic circular dichroism, with bulk magnetization determined by SQUID magnetometry. The results for two different manganese perovskites, La0.65A0.35MnO3 systems (A=Pb, Sr), epitaxially grown on LaAlO3 substrates compared. The results suggest that the magnetic circular dichroism results may not be representative of the bulk magnetization. Similar materials, but with a different secondary electron mean free path lengths or different surface compositions, may thus be expected to have different behavior in MCD or MXLD that depends on a photoyield for detection.

電池・イオン導電性材料 固体酸化物燃料電池のカソード材料としてのＬｎ１−ｘＳｒｘＭｎＯ３（Ｌｎ＝Ｌａ，Ｐｒ，Ｎｄ，Ｓｍ ａｎｄ Ｇｄ）

The perovskite type manganite systems, Ln1-xSrxMnO3 (Ln=La, Pr, Nd, Sm and Gd; 0.0≤x≤0.5) were studied as the electrode materials for solid oxide fuel cells (SOFC) from the view point of applications to the co-firing process of the electrolyte and electrode at higher temperature. The reactivity tests with yttria-stabilized zirconia (YSZ), no reaction product appeared between the Ln1-xSrxMnO3 perovskite and YSZ even at a high annealing temperature of 1400°C when the lanthanoid elements were Pr, Nd and Sm and the Sr content was around 30% (x=0.3). The adjustment of the thermal expansion rate of Ln1-xSrxMnO3 to YSZ, around x=0.1-0.2 in La1-xSrxMnO3, 0.3 in Pr1-xSrxMnO3 and Nd1-xSrxMnO3 and more than 0.4 in Sm1-xSrxMnO3 and Gd1-xSrxMnO3. The electrical conductivity reached to 200 S/cm at 1000°C for all Ln0.7Sr0.3MnO3 systems. The polarization measurements as an air electrode showed no significant dependence on the kind of lanthanoid elements. In the point of the electrode activity, high electrical conductivity, and low reactivity and good compatibility with YSZ, Pr0.7Sr0.3MnO3 and Nd0.7Sr0.3MnO3 are considered to be the most suitable electrode materials for the co-firing process.

A-Site Ordered, Perovskite-Like Manganites Grown by PLD or Laser-MBE: Their Growth, Structural and Physical Characterization

AbstractUsing both a “classical” pulsed laser deposition process and a laser-MBE process, superlattices in the Pr0.5Sr0.5MnO3 system were grown from PrMnO3 and SrMnO3 targets. A-site ordering of perovskite-like manganite was achieved using both deposition processes. However the electric and magnetic properties of the superlattices are shown to be strongly dependent on the growth process.

An Ion Conducted Tour through LaMO3 Perovskite-based Oxide Materials

This paper will review recent atomistic simulations of the oxygen ion transport and defect properties of the LaMO3(M = Mn, Co, Ga) perovskite-structured materials. Both static lattice and molecular dynamics techniques are used which have been applied previously to a rich variety of ceramic oxides. The mechanistic features and energetics of oxygen vacancy migration are examined in relation to ion size factors and lattice relaxation. The oxidation reaction in doped LaMO3 involving the creation of hole species from oxygen vacancies is also considered. Finally, MD simulations are used to yield information on oxygen diffusion coefficients and ion trajectories in the La1−x Sr x MnO3 system.

Cu doping effect on Mn sites of La2/3Ca1/3 MnO3 system

The temperature dependence of resistance and magnetoresistance at 77 K for Cu-doped La2/3Ca1/3Mn1-xCuxO3 have been investigated. Besides the transition similar to the Cu-free sample at ≈260 K, a new transition at lower temperature appears for Cu-doped samples. The new transition moves toward low temperature with increasing of Cu content. A new conductive proceeding related to Cu ion may exist. Magnetoresistance at liquid nitrogen shows thatMR increased three orders when × is changed from 0 to 0. 15. Moreover, the main variation of magnetoresistance is below the field of 1 T.

Anomalous Jahn-Teller distortions in La0.75Ca0.25MnO3 system: An X-ray absorption study

MnK-edge X-ray absorption near edge structure (XANES) measurements have been made to study the temperature-dependent lattice effects in the La0.75Ca0.25MnO3 system. The high-resolution XANES spectra recorded with high signal-to-noise ratio have allowed us to study the temperature dependence of the Jahn-Teller splitting indicated directly by the dipole forbidden pre-peaks corresponding to transition in Mn 3d states. The results show splitting of theeg state in its two orbitals (dx2 -y2 andd3z2-r2. The energy splitting shows anomalous temperature dependence across the giant magnetoresistance transition temperature.

Lattice effect on magnetism in CMR perovskite La 0.85 Sr 0.15 MnO z

Sr0.15MnO3 system has been investigated. Enlargements of lattice parameters with grain growth have been observed. Associated with this growth are a series of magnetic changes, including magnetization, Curie temperature Tc and superparamagnetic behavior. These phenomena may provide another route to understanding the relationship between structure and magnetism in the hole-doped manganese perovskites.

Investigation of strontium-doped La(Cr, Mn)O3 for solid oxide fuel cells

The (La, Sr) (Cr, Mn)O3 system was investigated in an effort to develop an interconnect and cathode materials for solid oxide fuel cells. Sintering studies were done in air at temperatures below 1500°C. Significant improvements in densification were observed with substitution of 50 mol% Mn for chromium and a density of 95% theoretical was achieved with the substitution of 70 mol% Mn for chromium in the La(Cr, Mn)O3 system. Electrical conductivity (d.c.) measurements were made as a function of temperature and oxygen activity. At 1000°C and 1 atm oxygen, the electrical conductivity ranged from 2.2–20 S cm−1 for LaCr0.8Mn0.4O3 and La0.9Sr0.1Cr0.2Mn0.8O3, respectively. All of the compositions showed similar dependence of electrical conductivity on the oxygen activity. Dependence was small at high oxygen activities; as the oxygen activity decreased, a break in electrical conductivity at 10−12 atm and 1000°C was observed, and then the electrical conductivity decreased asP O2 1/4 . Sintering and electrical conductivity studies indicate that La0.9Sr0.1Cr0.2Mn0.8O3 appears to be a candidate for solid oxide fuel cell applications.