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This paper reports the addition of NiO nanoparticles into the LCMO nanocomposites through a simplified methodology in the heat treatment process compared to the previous work. Structural analysis showed that LCMO and NiO co-existed in the samples without the formation of other phases and confirmed their composite structures. The grain size distribution of samples was observed to become narrower and left-skewed as the concentration of NiO nanoparticles increased. This indicates that the NiO nanoparticles were distributed near the grain boundaries or on the grain surfaces. The presence of La, Ca, Mn, O, and Ni was confirmed by EDX analysis, and no additional impurities were noticeable, which revealed that the composites here are chemically pure in the composition. Temperature dependence magnetisation measurement (100–300 K) revealed the occurrence of ferromagnetic to paramagnetic transition. The Curie temperature, TC recorded at 260 K for all samples. However, the metal–insulator transition temperature, TMI was found to decrease from 246 to 120 K as the NiO content increased. Magnetoresistance of composites was observed to enhance over a wide temperature range at 10 kOe. The findings of LCMO: NiO composites in this work can set up a new perspective and unlock its potential to be utilised in magnetic field sensor element functioning at a wide range of temperatures. [ABSTRACT FROM AUTHOR]

Polycrystalline Sm0.55Sr0.45MnO3 (SSMO) thin films (thickness ~ 100 nm) were prepared on nearly lattice matching LSAT (100) single crystal substrates by ultrasonic nebulized spray pyrolysis, and impact of oxygen vacancy on magnetic and high field magneto-transport properties are investigated. The X-ray diffraction θ‒2θ scan reveals that these films (i) have very good crystallinity, (ii) oriented along out-of-plane c-direction, and (iii) are under small tensile strain. The impact of oxygen vacancy results into (i) higher value of paramagnetic insulator (PMI) to ferromagnetic metal (FMM) transition temperature, i.e., TC/TIM, (ii) sharper PMI–FMM transition, as confirmed by higher temperature coefficient of resistance (TCR), (iii) higher value of magnetization and magnetic saturation moment, and (iv) higher value of magnetoresistance. The magnetic state at T < TC is akin to cluster glass, which is formed by the presence of charge-ordered–antiferromagnetic clusters in the ferromagnetic matrix. We suggest here that oxygen vacancy favors ferromagnetic metal phase while oxygen vacancy annihilation leads to antiferromagnetic–charge-ordered insulator phase. The observed results have been explained in terms of the growth condition-induced variations in the dimensionality and fractions of the competing ferromagnetic metal and antiferromagnetic–charge-ordered insulator phases. [ABSTRACT FROM AUTHOR]

The crystalline samples of La0.67Ca0.33Mn1-xNixO3 (x = 0, 0.05, and 0.1) manganites were prepared by conventional solid-state reaction method. The analysis of X-ray diffraction spectra revealed that all the prepared samples are single phased in nature and have acquired orthorhombic structure with space group Pbnm. Temperature-dependent dc resistivity measurements infer metallic nature of the samples in the lower temperature region (T > 50 K) where metal to insulator transition (TMI) occurs at temperature 238 K, 204 K, and 187 K for x = 0, 0.05, and 0.1, respectively. For the temperature below 50 K, a kind of transition from paramagnetic insulator to the ferromagnetic metallic phase was observed in all the materials. The application of magnetic field of 8 T indicates the shift of TMI toward the higher temperature region with high reduction in resistivity due to suppression of any thermal agitations present. The resistivity data analysis for conduction mechanism above 50 K infers that the grain/domain boundary scattering processes play a dominant role in the the metallic region. However, the analysis of the region below 50 K infers that weak localization effect is the responsible factor in conduction phenomena. Isothermal at 300 K for magnetoresistance study conveys that the pristine La0.67Ca0.33MnO3 manganite exhibits larger MR effect with rise in magnetic field compared to doped ones. [ABSTRACT FROM AUTHOR]

Curvature-based three-dimensional cardiovascular magnetic resonance (CMR) allows regional function characterization without an external spatial frame of reference. However, introduction of this modality into clinical practice is hampered by lack of reference values. We aim to establish normal ranges for 3D left ventricular (LV) regional parameters in relation to age and gender for 171 healthy subjects. LV geometrical reconstruction and automatic calculation of regional parameters were implemented by in-house software (CardioWerkz) using stacks of short-axis cine slices. Parameter normal ranges were stratified by gender and age categories (≤44, 45–64, 65–74 and 75–84 years). Our software had excellent intra- and inter-observer agreement. Ageing was significantly associated with increases in end-systolic (ES) curvedness (CES) and area strain (AS) with higher rates of increase in males, end-diastolic (ED) and ES wall thickness (WTED, WTES) with higher rates of increase in females, and reductions in ED and ES wall stress indices (σi,ED) with higher rates of increase in females. Females exhibited greater ED curvedness, CES, σi,ED and AS than males, but smaller WTED and WTES. Age × gender interaction was not observed for any parameter. This study establishes age and gender specific reference values for 3D LV regional parameters using CMR without additional image acquisition. [ABSTRACT FROM AUTHOR]

By using La(NO3)3•6H2O, Ca(NO3)2•4H2O, and Mn(CH3COO)2•4H2O as starting raw materials together with methanol, three kinds of La0.67Ca0.33MnO3 (LCMO) solutions, denoted as LCMO–BzAc, LCMO–AcAc, and LCMO–BPY, respectively, were obtained. The samples were fabricated via the photosensitive solution method with benzoylacetone (BzAc), acetylacetone (AcAc), and 2, 2′-bipyridine (BPY) as chelating reagents. The chelation mechanism of the metal ions was investigated via ultraviolet spectroscopy. The photosensitive compounds were decomposed after UV exposure and their products reduced the solubility of the LCMO gel films in organic solvents. The patterned LCMO thin films were then fabricated by using the self-photosensitive properties of their gel films. Through the mask micromachining process, the LCMO micropatterns prepared by using the LCMO–BzAc solution exhibited the highest quality. Moreover, they also presented good performance when the mask-free method was employed. The magnetic properties of the micropatterned LCMO films were investigated in detail and the results revealed that the micropatterning did not influence their saturation magnetization. Highlights: Patterned La0.67Ca0.33MnO3 (LCMO) thin films were prepared. BzAc was the best complexing agent for fabrication of high-quality patterns. Micro-patterned did not influence the LCMO film's saturation magnetization value. [ABSTRACT FROM AUTHOR]

The effects of paired substitution of 3d10 cations (Zn0.52+Ge0.54+) or 2p6 and 3p6 cations (Mg0.52+Ti0.54+) for manganese in polycrystalline manganites of specifically designed systems La0.8−xSr0.2+xMn0.8−2x−2γ3+Mn0.2+x+2γ4+×(Me0.52+Me0.54+)xO3+γ on their electromagnetic parameters are studied and compared. Temperature dependences of the resistance, magnetoresistance and magnetostriction constant are measured. In the proposed systems, the linear rise of strontium concentration simultaneously with increasing number of substituents allows high characteristics of manganites to be maintained owing to the increase in the concentration of free charge carriers, through which ferromagnetic double exchange interaction is carried out. The data obtained are also compared with the properties of Ga3+(3d10)-substituted manganites as peculiar standards. All sintered (Zn,Ge)-containing manganites in the temperature range from 100 to 293 K have metallic type of conductivity, while (Mg,Ti)-substituted samples exhibit semiconducting features, and Ga-containing compositions reveal a “metal-semiconductor” transition point (Tms). The annealing under conditions ensuring stoichiometric oxygen content leads to the shift of this transition toward lower temperatures in manganites with 3d10 substituents and to the increase in Tms in compositions with substituting p6 cations. In the investigated systems, the absolute values of negative magnetoresistance up to ~90-200% at 120-150 K in the field of 9.2 kOe are obtained, and the linear magnetostriction constant reaches record values of about 10-3 in the field of 4.6 kOe. Manganite La0.65Sr0.35Mn0.85Ga0.15O3 with a weak temperature dependence of magnetoresistance of ~20% at room temperatures is of particular service for magnetic field sensors. Possible approaches to the interpretation of established regularities demonstrating the role of electronic configurations of substituents for manganese in the formation of the properties of manganites and interesting for the development of new materials for electronics are discussed. [ABSTRACT FROM AUTHOR]

Objectives: To compare accelerated real-time cardiac MRI (CMR) using sparse spatial and temporal undersampling and non-linear iterative SENSE reconstruction (RT IS SENSE) with real-time CMR (RT) and segmented CMR (SEG) in a cohort that included atrial fibrillation (AF) patients.Methods: We evaluated 27 subjects, including 11 AF patients, by acquiring steady-state free precession cine images covering the left ventricle (LV) at 1.5 T with SEG (acceleration factor 2, TR 42 ms, 1.8 × 1.8 × 6 mm3), RT (acceleration factor 3, TR 62 ms, 3.0 × 3.0 × 7 mm3), and RT IS SENSE (acceleration factor 9.9-12, TR 42 ms, 2.0 × 2.0 × 7 mm3). We performed quantitative LV functional analysis in sinus rhythm (SR) patients and qualitatively scored image quality, noise and artefact using a 5-point Likert scale in the complete cohort and AF and SR subgroups.Results: There was no difference between LV functional parameters between acquisitions in SR patients. RT IS SENSE short-axis image quality was superior to SEG (4.5 ± 0.6 vs. 3.9 ± 1.1, p = 0.007) and RT (3.8 ± 0.4, p = 0.003). There was reduced artefact in RT IS SENSE compared to SEG (4.4 ± 0.6 vs. 3.8 ± 1.2, p = 0.04), driven by arrhythmia performance. RT IS SENSE short-axis image quality was superior to SEG (4.6 ± 0.5 vs. 3.1 ± 1.0, p < 0.001) in the AF subgroup.Conclusion: Accelerated real-time CMR with iterative sparse SENSE provides excellent clinical performance, especially in patients with AF.Key Points: • Iterative sparse SENSE significantly accelerates real-time cardiovascular MRI acquisitions. • It provides excellent qualitative and quantitative performance in sinus rhythm patients. • It outperforms standard segmented acquisitions in patients with atrial fibrillation. • It improves the trade-off between temporal and spatial resolution in real-time imaging. [ABSTRACT FROM AUTHOR]

The present communication deals with particle size-dependent zero-field cooled exchange effect in LaFeO (LFO). LFO nanoparticles were prepared by PVA-based sol-gel method. The sample was calcined at different temperatures (700, 750, and 800 C) to tune the average particle size. The detailed crystal structural and their geometrical parameters were examined by means of Rietveld refinement using x-ray diffraction data. The different techniques such as Scherrer's method, Williamson Hall method, FESEM, and TEM were applied to accurately determine the average particle size. Zero-field cooled exchange bias and weak ferromagnetism in antiferromagnetic nanoparticles was observed for all samples using hysteresis loop measurement. The training effect was studied to confirm that the loop shift originates due to exchange bias. Exchange bias as well as coercivity are strongly related to the particle size at low and room temperature. The results clearly demonstrate that the process of calcination tailor the overall properties of material which makes it a promising candidate for device applications. [ABSTRACT FROM AUTHOR]

This paper presents a detailed study on the structural, magnetic, and critical behavior and magnetocaloric effect of LaSrMnCuO prepared by solid-state reaction method. X-ray diffraction patterns indicate that Cu-doped manganite crystallizes to a single phase with a rhombohedral structure. Critical components β, γ, and δ were determined by using modified Arrott plot, Kouvel-Fisher method, and critical isotherm analyses. These components are consistent with their corresponding values and were validated by Widom scaling law and scaling theory. The deduced critical exponents ( β = 0.456, γ = 0.9912, and δ = 3.206) are also close to their corresponding theoretical values predicted by mean-field model, indicating that long-range interaction dominates the critical behavior of the LSMCO system. Spontaneous magnetization was determined by two methods. One method is based on magnetic entropy change under different magnetic fields, and the other method is based on classical extrapolation from the Arrott plot. The two methods are in excellent agreement, confirming the validity of the deduction of spontaneous magnetization using the magnetic entropy change. [ABSTRACT FROM AUTHOR]

We designed and fabricated a new uniaxial pressure device for doing resistivity measurements under uniaxial pressure at a high-temperature region (300 K–800 K). This uniaxial pressure device was tested with La0.95Sr0.05MnO3 and we have measured the resistivity in the temperature region (400 K–700 K). We found the drastic variation in the John-Teller Distortion by increasing the pressure and this may be due to the increase in disorder in the structure. The disorder increases due to non-uniform variation of Mn–O bond length in the structure. [ABSTRACT FROM AUTHOR]

Thin films of PrSrMnO have been prepared on (100)-oriented single crystalline SrTiO and LaAlO substrates using pulsed laser deposition. X-ray diffraction analysis reveals formation of thin films with c-axis orientation. The magnetotransport properties of the thin films have been studied in comparison to the polycrystalline bulk sample. Thin films exhibit substantially larger colossal magnetoresistance than the bulk, and the effect is observed to be more pronounced in the film which experiences a larger strain. The resistivity behavior above the metal-insulator transition temperature for the bulk as well as thin films samples follows adiabatic small polaron hopping mechanism for conduction. On the other hand, resistivity in the low-temperature metallic region could be explained considering the electron-magnon and electron-electron scattering contributions to resistivity. [ABSTRACT FROM AUTHOR]

The structural, magnetic and magnetocaloric properties of the polycrystalline PrCaBiMnO ( x = 0, 0.1, 0.18, 0.26 and 0.32) samples were studied. X-ray analyses indicated that all samples have a single phase of orthorhombic symmetry. The charge-order transition was observed for the x = 0 sample at T = 200 K, and it disappears with further Bi doping of the sample. The Curie temperature, saturation magnetisation and magnetocaloric effect decrease with increasing Bi content. The decrease in Curie temperature and saturation magnetisation was attributed to magnetic inhomogeneity and weakening of double-exchange interaction in the Bi-doped samples. The decrease in saturation magnetisation and the changed nature of phase transition give rise to a decrease in magnetic entropy change. [ABSTRACT FROM AUTHOR]

We investigate nonequilibrium processes of self-heating induced by electric current in ferromagnetic semiconductors exhibiting colossal magnetoresistance (CMR) in the vicinity of the Curie temperature. The heat balance equation is solved taking into consideration localized states that appear as a result of scattering from magnetic inhomogeneities and are characterized by a percolation threshold proportional to the amplitude of spin fluctuations. The appearance of N-shaped current-voltage characteristics and hysteresis in the dependence of magnetization on electric potential difference, which are caused by the emergence of a 'hot' (with respect to internal temperature) semiconductor paramagnetic phase, is revealed in the steady-state regime. The possibility of suppression of the effect of colossal magnetoresistance with increasing potential difference is indicated. The onset of self-oscillation of current and magnetization with decreasing transverse dimensions of the sample is demonstrated. [ABSTRACT FROM AUTHOR]

The magnetoresistance of a heterostructure comprising parallel-connected epitaxial graphene on a metal substrate and graphene on a dielectric substrate has been studied in the framework of the Drude theory. The phenomenon of colossal magnetoresistance in this system is predicted on the basis of previous results for the conductivity of epitaxial graphene. [ABSTRACT FROM AUTHOR]

Colossal magnetoresistance (CMR) ceramics with starting composition of LaBiCeMnO ( x = 0-0.15) were synthesized using the conventional solid-state synthesis method to investigate the effect of Bi substitution on their magnetic and electrical transport properties. The undoped sample ( x = 0) showed paramagnetic to ferromagnetic (PM-FM) transition at Curie temperature, T = 248 K and metal to insulator (MI) transition at T = 231 K which decreases with Bi content (0 < x < 0.15) indicating weakening of FM phase. At x = 0.15, the susceptibility, χ′ was observed to decrease below 83 K which indicates presence of antiferromagnetic (AFM) clusters in the sample. The decrease in T and T is suggested to be due to the weakening of DE-like interaction involving Mn and Mn as a result of the hybridization between Bi 6 s lone pair with O orbital which increases electron localization. Fitting of the experimental data in the metallic region to scattering models suggested scattering involving electron-electron, electron-magnon, Kondo-like spin-dependant scattering, and electron-phonon interaction. On the other hand, fitting in the insulating region suggests resistivity behavior obeys the adiabatic small polaron hopping (SPH) model. [ABSTRACT FROM AUTHOR]

(LaSrMnO)/(ZrO) ( x = 0.0-0.150, step 0.025) composites have been prepared via solid state reaction process. The X-ray diffraction and scanning electron microscopic observations indicate that there are ZrO grains separated from LaSrMnO matrix. It has been found that the inclusion of ZrO content decreases the conductivity, magnetization and metal-semiconductor transition, whereas it increases the low field magnetoresistance. Possible effects of grain boundaries on the low field magnetoresistance have been discussed. The small ZrO grains are trapped between LaSrMnO grains may be acting as a barrier for spin-polarized tunneling and enhance the low-field magnetoresistance. [ABSTRACT FROM AUTHOR]

High-resolution neutron powder diffraction is used to investigate the phase separation and microscopic nature of the magnetoresistance in complex half-doped manganites. Investigations are performed by the example of SmPrSrMnO exhibiting the colossal magnetoresistance effect. The structural transition from a high-temperature orthorhombic Pbnm phase to a mixed phase containing two (orthorhombic Pbnm and monoclinic P2/ m) phases is revealed. A gradual decrease in the amount of the orthorhombic phase and, consequently, an increase in the amount of the monoclinic phase are observed with decreasing temperature. Redistribution of the two phases ceases below T ≈ 100 K. Low-temperature analysis of the magnetic contribution to the experimental neutron-diffraction patterns indicates that the magnetic ground state of the compound under study is phase-separated and corresponds to a mixed state involving three magnetic phases formed at different temperatures: a ferromagnetic phase, A- type antiferromagnetic, and CE- type charge ordered antiferromagnetic phases with charge-orbital ordering. Ferromagnetic ordering arises near room temperature in the orthorhombic Pbnm phase and manifests itself only until helium temperatures. The A- and CE-types antiferromagnetic states ( T ≈ 170 and 120 K, respectively) appear in the monoclinic crystallographic phase. [ABSTRACT FROM AUTHOR]

The cooperative Jahn-Teller effect (CJTE) refers to the correlation of distortions arising from individual Jahn-Teller centres in complex compounds. The effect usually induces strong coupling between the static or dynamic charge, orbital and magnetic ordering, which has been related to many important phenomena such as colossal magnetoresistance and superconductivity. Here we report a Na5/8MnO2 superstructure with a pronounced static CJTE that is coupled to an unusual Na vacancy ordering. We visualize this coupled distortion and Na ordering down to the atomic scale. The Mn planes are periodically distorted by a charge modulation on the Mn stripes, which in turn drives an unusually large displacement of some Na ions through long-ranged Na-O-Mn3+-O-Na interactions into a highly distorted octahedral site. At lower temperatures, magnetic order appears, in which Mn atomic stripes with different magnetic couplings are interwoven with each other. Our work demonstrates the strong interaction between alkali ordering, displacement, and electronic and magnetic structure, and underlines the important role that structural details play in determining electronic behaviour. [ABSTRACT FROM AUTHOR]

The cooperative Jahn-Teller effect (CJTE) refers to the correlation of distortions arising from individual Jahn-Teller centres in complex compounds. The effect usually induces strong coupling between the static or dynamic charge, orbital and magnetic ordering, which has been related to many important phenomena such as colossal magnetoresistance and superconductivity. Here we report a Na5/8MnO2 superstructure with a pronounced static CJTE that is coupled to an unusual Na vacancy ordering. We visualize this coupled distortion and Na ordering down to the atomic scale. The Mn planes are periodically distorted by a charge modulation on the Mn stripes, which in turn drives an unusually large displacement of some Na ions through long-ranged Na-O-Mn3+-O-Na interactions into a highly distorted octahedral site. At lower temperatures, magnetic order appears, in which Mn atomic stripes with different magnetic couplings are interwoven with each other. Our work demonstrates the strong interaction between alkali ordering, displacement, and electronic and magnetic structure, and underlines the important role that structural details play in determining electronic behaviour. [ABSTRACT FROM AUTHOR]

Colossal magnetoresistance LaSrMnO (LSMO) thin films were directly grown on MgO(100), Si(100) wafer and glass substrates by pulsed laser deposition technique. The films were characterized using X-ray diffraction (XRD), field emission-scanning electron microscope and atomic force microscopy (AFM). The electrical and magnetic properties of the films are studied. From the XRD patterns, the films are found to be polycrystalline single-phases. The surface appears porous and cauliflower-like morphology for all LSMO films. From AFM images, the LSMO films deposited on glass substrate were presented smooth morphologies of the top surfaces as comparing with the films were deposited on Si(100) and MgO(100). The highest magnetoresistance (MR) value obtained was −17.21 % for LSMO/MgO film followed by −15.65 % for LSMO/Si and −14.60 % for LSMO/Cg films at 80 K in a 1T magnetic field. Phase transition temperature (T) is 224 K for LSMO/MgO, 200 K for LSMO/Si and above room temperature for films deposited on glass substrates. The films exhibit ferromagnetic transition at a temperature (T) around 363 K for LSMO/MgO, 307 K for LSMO/Si and 352 K for LSMO/Cg thin film. T such as 363 and 352 K are the high T that has ever been reported for LSMO films deposited on MgO substrate with high lattice mismatch parameter and glass substrates with amorphous nature. [ABSTRACT FROM AUTHOR]

Functional perovskite oxides are recognized for their stunningly rich physics and for their potential as next-generation electronic materials. Their properties include high Tc superconductivity, colossal magnetoresistance, record-high dielectric/ferroelectric/piezoelectric performances, multiferroic behavior, resistive switching behavior, giant thermoelectric and magnetocaloric effects, giant ionic conduction, and catalytic behavior. Due to their intrinsic chemical and crystal similarities, functional oxides can be stacked in multilayer heterostructures exhibiting an astonishing degree of epitaxial perfection. Such artificial systems not only allow one to combine in a single device the functionalities of their individual layers, but often reveal an even wider range of emergent novel properties that can be surprisingly different from those of the single building blocks. The goal of this issue of MRS Bulletin is to present the state of the art of oxide interfaces in inscience and technology. Here we provide an introduction to their properties, serving as a base for the following topical articles. [ABSTRACT FROM PUBLISHER]

We have developed a high-performance laser energy meter based on anisotropic Seebeck effect in a strongly correlated electronic (SCE) thin film. SCE thin films, typically represented by high-temperature superconductor (HTS) cuprate and colossal magnetoresistance (CMR) manganite thin films, demonstrate tremendous anisotropic Seebeck effect. In this study, a LaCaMnO thin film grown on a tilted LaAlO substrate is tested with the fundamental, the second, the third, and the fourth harmonics (1064, 532, 355, 266 nm, respectively) of a Q-switched Nd:YAG laser over a wide range of temperatures from room temperature to 16 K. The peak-value of the laser-induced thermoelectric voltage signal shows a good linear relationship with the laser energy per pulse in the measured wavelength and temperature ranges. The combined advantages over other commercial laser detectors such as nanosecond-order response and spectrally broad and flat response over a wide range of temperatures, in situ real-time measurement, and energy savings, make the device an ideal candidate for next-generation laser detectors and laser power/energy meters. [ABSTRACT FROM AUTHOR]

Perovskite manganite composites containing polymer binder (epoxy resin) and additional metal (Sn) were prepared using a novel bonded method. The magnetoresistance (MR) for the sample containing 4 % polymer binder and 10 % metal was as high as 20 % and nonsensitive to temperature in the temperature range of 50–300 K under applied field of 3 kOe. The nontemperature-sensitive and large MR could be ascribed to the contribution of polymer and metal, respectively. When temperature was higher than 300 K, intrinsic colossal magnetoresistance effect was observed. [ABSTRACT FROM AUTHOR]

The effects of silver doping on the magnetotransport and thermopower of LaAgMnO (0.05≤ x≤0.30) have been investigated. For the sample with x=0.05, temperature dependent resistivity exhibits an insulating behavior, while thermopower is found to be large and negative over the measured temperature range. An increase in the Ag doping enhances the conductivity and shifts the metal-insulator transition temperature toward high temperature side. The low temperature thermopower data has been explained in terms of diffusion, magnon drag, and phonon drag effects and found that the magnon drag effect dominates in this region. Finally, the electrical transport in the high temperature region has been analyzed by using adiabatic small polaron hopping mechanism. [ABSTRACT FROM AUTHOR]

We have introduced the hole-induced magnetic soliton by using the gauge-invariant Lagrangian density and the path-integral method. The percolation-like dynamics of hole-induced magnetic solitons and the colossal magnetoresistance mechanism in doped manganites have been proposed from the standpoint of the random resistor network and percolation-scaling method. The long-relaxation behaviour of the spin has been discussed by using the effective Hamiltonian and the frustration-limited domain model. [ABSTRACT FROM AUTHOR]

In this paper, the existence of Griffiths phase and variation of ferromagnetism have been studied for LaCaMnO nanoparticles annealed at different temperatures. It is detected by x-ray diffraction patterns that the increasing of annealing temperature induces the increment of grain size. The magnetization as a function of temperature demonstrates that magnitude of magnetization at low temperature is decreased as the annealing temperature increases, which is explained by the core-shell model. The temperature dependence of inverse susceptibility of those samples manifests that the Griffiths phase occurs for the samples annealed at temperatures 900 °C and 1150 °C and it disappears for the sample annealed at 1350 °C. The reduction of Griffiths phase with increasing of annealing temperature indicates the suppression of quenched disorder after annealing, which may be related to the lower degree of disorder, redistribution of magnetic ions, and weaker hybridization of O 2p states with its near-neighbor atoms. As to the disappearance of Griffiths phase, competition between paramagnetic, ferromagnetic, and antiferromagnetic phases plays a very important role. [ABSTRACT FROM AUTHOR]

By finely controlling the deposition parameters in the pulsed electron deposition process, granular LaCaMnO (LCMO) film was grown on silicon substrates. The substrate temperature, ambient pressure in the deposition chamber and acceleration potential for the electron beam were all found to affect the grain size of the film, resulting in different morphologies of the samples. Transport properties of the obtained granular films, especially the magnetoresistance (MR), were studied. Prominent low-field MR was observed in all samples, indicating the forming of grain boundaries in the sample. The low-field MR show great sensitive to the morphology evolution, which reaches the highest value of about 40% for the sample with the grain size of about 250 nm. More interestingly, positive-MR ( p-MR) was also detected above 300 K when low magnetic field applying, whereas it disappeared with higher magnetic field applied up to 1.5 and 2 Tesla. Instead of the spinpolarized tunneling process being commonly regarded as a responsible reason, lattice mismatch between LCMO film and silicon substrate appears to be the origin of the p-MR [ABSTRACT FROM AUTHOR]

brief review of properties of the ferromagnetic manganites LaCaMnO is given. Lattice properties, magnetic properties, transport phenomena, magnetic resonance, and the results of neutron diffraction and optical studies are considered. Special attention is paid to effects observed near the Curie temperature. [ABSTRACT FROM AUTHOR]

The temperature dependence of the resistivity ( ρ) and magneto-resistance (MR) effect of LaLiMnO ( x=0.05, 0.1, 0.15, 0.2 & 0.25 at.%) fixed valence doped compounds were studied between 80 and 320 K. X-ray powder diffraction (XRD) at room temperature shows that the samples are single phase. The resistivity of all samples with and without magnetic field shows a metal-semiconductor (M-S) transition for all compositions. In addition, the replacement of the Li-substitution results in a reduction of the transition temperature T and increases ρ. In the magnetic field of 0.5 Tesla a large negative magnetoresistance (MR=50%) was observed, which is encouraging for potential application of colossal magnetoresistance (CMR) material at low fields. We determine the activation energy ( E) in the semiconductor region. [ABSTRACT FROM AUTHOR]

Y and Sr co-doped La2/3Ca1/3MnO3 films with different A-site cation disorder were deposited on Yttrium-stabilized ZrO2 (YSZ) single crystal substrate by modified off-axis rf magnetron sputtering technology. The influences of A-site cation disorder and biaxial strain on the surface morphologies and transport properties are discussed in detail. At high temperature, the mechanism of conduction is changed from the small polaron hopping model to the variable-range hopping model with increasing cation disorder, which reveals that cation disorder induces carrier localization. The Curie temperature and the magnetoresistance decrease with the increase of cation disorder. It reveals the variation of phase separation to be caused by the increasing cation disorder which suppresses the long-range FM metal state. [ABSTRACT FROM AUTHOR]

The magnetoresistance ( MR) of polycrystalline La0.83Sr0.17MnO3 thin films have been studied in high pulsed magnetic fields up to 38 T in the temperature range 100–300 K. The lucalox substrates were used to obtain polycrystalline structures with naturally formed grain boundaries (GBs) and crystallites whose dimensions were determined by film deposition temperature. It was found that the MR value is highest in the films having smallest crystallites. The main behaviour of high-field MR was analysed using modified Mott’s hopping model assuming that the GBs might be ferromagnetic with a Curie temperature TC being reduced in comparison with that of the crystallites interior. [ABSTRACT FROM AUTHOR]

Systematical investigations of zero-field resistivity, magnetoresistance and magnetization were performed for a typical manganese compound La2/3Ca1/3MnO3. It is argued that the common origin for insulator-metal and paramagenetic ferromagnetic-transitions as well as colossal magnetoresistance is due to the formation of ferromagnetic clusters in the paramagnetic background. The transition to metallic state is resulted from percolation of ferromagnetic metallic clusters, while the colossal magnetoresistance is due to the application of magnetic field, which accelerates the growth of ferromagnetic metallic clusters and causes the shift of the onset temperature for the metallic percolation to higher temperature. Based on the random resistor network model, the zero-field resistivity versus temperature dependence is simulated by using experimental parameters, and experimental data well agree with those in whole temperature range, giving a strong support to our approach. [ABSTRACT FROM AUTHOR]

The LaMn1− xTe xO3+ δ ( x=0.1, 0.2, 0.3) were synthesized using solid-state reaction method for the first time. X-ray photoemission spectrum (XPS) shows that in the samples the Te ions have a valence of Te4+, and Mn3+ ions are partly converted into Mn2+ and Mn4+ due to the excess oxygen and Te doping. The magnetotransport associated with Mn2+, Mn3+ and Mn4+ was investigated. The experimental results show that the samples are insulator at 0 T when the amount of Mn3+ is much larger or less than the sum of Mn2+ and Mn4+; by contrast, the samples display metal to insulator transition with increasing temperature when the amount of Mn3+ is close to the sum of Mn2+ and Mn4+. These anomalous magnetotransport behaviors were analyzed in the frame of the double-exchange (DE) mechanism. [ABSTRACT FROM AUTHOR]

We propose a model to study the magnetic phase transition in the Colossal-Magneto-Resistance (CMR) material of general type R1− x A x MnO3 (R = La, Sm, Nd; A = Ca, Sr, Ba). The model Hamiltonian consists of a Charge Density Wave (CDW) gap in the e g -band and the strong magnetic field due to the spin ordering in the localized t g core electrons. The Hamiltonian is solved by using Zubarev’s Green’s function technique to calculate CDW gap ( Δ) and magnetization ( M d ) in t 2 g band. Both of them are solved self-consistently. Their combined effect on the temperature dependent magnetization ( M c ) due to the e g band electrons is investigated. Both the magnitude and the transition temperature of ( M c ) are strongly influenced by both Δ and M d . Hence the hopping of the band electrons are strongly controlled by these two long range interactions. The results are discussed by varying the model parameters of the manganite system. [ABSTRACT FROM AUTHOR]

La2/3Ca1/3MnO3 films were prepared using a conventional paint-on method on alumina and monocrystalline TiSrO3 substrates. A significant difference between the peak resistivity temperature T p=178 K and the magnetic transition temperature T c=240 K was found in contrast to single crystal samples. The behavior of the magnetoresistance with temperature also differs from that found in bulk samples. Although the films show significant granular morphology differences, their transport and magnetoresistive properties are very similar. Maximum magnetoresistance ratios of 16% and 10% at 0.3 T and 77 K were obtained for films deposited on alumina and TiSrO3 substrates, respectively. Magnetization measurements above T c show a nonlinear behavior, consistent with the presence of ferromagnetic inhomogeneities within the paramagnetic phase. These results suggest that, in addition to the importance of grain boundary scattering in determining the magnetoresistance at low fields, microscopic inhomogeneity plays a role in determining magnetotransport properties. [ABSTRACT FROM AUTHOR]

A comparative study for two different series, La0.67Ca0.33Mn1− x Cr x O3 and La0.67+ x Ca0.33− x Mn1− x Cr x O3, is performed with χ changing from 0.04 to 0.08 through measurements of zero-field resistivity (π), magnetoresistance (MR) and ac susceptibility ( χ) as functions of temperature ( T). For the second group, a single insulator-metal transition was characterized by the resistivity maximum appears in π vs. T curve. For the first group, besides the resistivity peak appearing at higher temperatures, the sample shows evidence for the existence of another peak appearing at lower temperatures. Compared to the first group, the second group shows a significant enhancement in MR effect, while the measurement of χ-T dependence does not display obvious differences for the two series. Different behaviors observed in the two series are discussed by considering possible exchange interaction between Mn3+ ion and Cr3+ ion. [ABSTRACT FROM AUTHOR]

High quality La0.67Ca0.33MnO3 (LCMO) film was deposited via a novel pulsed electron deposition technique on SrTiO3(100) single crystal substrate. The micro-bridge with different widths was fabricated by using electron beam lithography (EBL) technique and their transport properties were studied. For the micro-bridges with width of 2 and 1.5 μm, the insulator-to-metal transition temperature ( T P) keeps unchanged compared with the film. For the micro-bridges with width of 1 μm, the T P shifts towards the lower temperature by 50 K. When the width decreases down to 500 nm, the insulator-to-metal transition disappears. The magnetoresistance behavior of these micro-bridges was studied, and the results show that the low field magnetoresistance (LFMR) decreases and the high field magnetoresistances (HFMR) keep almost unchanged as the width of micro-bridge is reduced. [ABSTRACT FROM AUTHOR]

Earlier theoretical approaches to manganites mainly stem from magnetic framework in which the electronic transports are thought to be spin-dependent and the double exchange plays a vital role. However, quite a number of experimental observations cannot be explained in the magnetic framework, yet. For example, multiplicate insulator-metal transitions and resistivity reduction induced by perturbations other than magnetic field, such as electric current, are not well understood in this framework. Here we present a comprehensive analysis on the magnetic framework and give a Monte Carlo study on the resistivity of a charge ordered/disordered model without accounting for the spin degree of freedom. The result shows a colossal resistivity change as a resultant of the transition between two types of insulated states. This transition has intrinsic difference from the popular insulated-to-metallic transition in the magnetic framework. The present scenario can be used to explain some experimental facts for electronic transports in manganites, which are not accessible in the magnetic framework. [ABSTRACT FROM AUTHOR]

A phenomenological model based on phase separation between ferromagnetic metallic and paramagnetic insulating domains was applied to analyze the electrical transport and colossal magnetoresistance for mixed-valent manganites of RE2/3 AE1/3 MnO3. The results show that the model can yield results in agreement with experimental observations in these manganites. The present approach provides a simple picture to visualize the reason that the temperature dependence of resistance (with and without applied magnetic fields) in these compounds has the peculiar shape, without invoking any complicated concept. [ABSTRACT FROM AUTHOR]

Colossal magnetoresistance (CMR) composites form an interesting field of study. The intrinsic CMR, governed by the intragrain transport of the conduction electrons through the double exchange, limits its application owing to the high field requirement and generally low transition temperatures. Extrinsic CMR, a function of the intergrain transport between ferromagnetic (FM) particles, plays a crucial role in enhancing low field magnetoresistance (LFMR) or increasing room temperature magnetoresistance. Since extrinsic CMR is a grain boundary controlled phenomena, magnetically dirty grain boundaries in the virgin state of the sample help in achieving a high LFMR or increase the field sensitivity. In this article, we give the properties of different composites of magnetoresistive LCMO or LSMO where the second component is (a) an insulating phase, (b) a conducting phase, (c) a nonmagnetic phase and (d) a magnetic phase. We present here some of our recent work on CMR composites where the CMR phase is chosen as LCMO and SiO, ZnO, ZrO and SiCN have been used as the different second phase of the composites. We summarise some of the salient features of the results. [ABSTRACT FROM AUTHOR]

Manganites of the LACaMnO family show a variety of new and poorly understood electronic, magnetic and structural effects. Here we outline a new approach recently proposed by us, where we argue that due to strong Jahn-Teller (JT) coupling with phonons the twofold degenerate e states at the Mn sites dynamically reorganize themselves into localised, JT polarons l with exponentially small inter-site hopping, and band-like, nonpolaronic states b, leading to a new 2-band model for manganites which includes strong Coulomb and Hund's couplings. We also discuss some results from a dynamical mean-field theory treatment of the model which explains quantitatively a wide variety of experimental results, including insulator-metal transitions and CMR, in terms of the influence of physical conditions on the relative energies and occupation of the l and b states. We argue that this microscopic coexistence of the two types of electronic states, and their relative occupation and spatial correlation is the key to manganite physics. [ABSTRACT FROM AUTHOR]

We present a study of the paramagnetic to ferromagnetic transition in the CMR compound La0.65Ca0.35MnO3 and its dependence on magnetic field and oxygen mass. The transition is characterized by two temperatures, the thermodynamic transition temperature at Tc, obtained from specific heat and thermal expansion data, and the resistive transition obtained from the resistivity maximum. The resistive transition occurs well within the paramagnetic range. The magnetic susceptibility in the paramagnetic range is isotope dependent up to 400 K. The magnitude of the Curie-Weiss constant indicates the presence of small clusters of about 4–5 unit cells. The resistive transition occurs when the percolation limit for these clusters is reached. [ABSTRACT FROM AUTHOR]

In this study we present some results obtained from AC susceptibility (χAC) and transport measurements in polycrystalline samples of La0.7Ca0.3MnO3, in order to better investigate the relations between AC magnetic susceptibility and electrical transport measurements. In addition, it was also studied the inter- and intragranular characteristics of polycrystalline samples. Comparison among results obtained from χAC and transport measurements confirm that χ″ is an excellent tool to identify not only sample quality, but also to resolve between intra- and intergranular contributions. Besides that, experiments based on χAC are easier to prepare and perform than those based on the conventional transport measurments. In this context, it is appropriate to establish a link between transport and magnetic properties. [ABSTRACT FROM AUTHOR]

High purity powder of manganese perovskite, La2/3Ca1/3MnO3, is prepared using a modified sol-gel synthesis based on the dissolution and homogenisation of metal salts in ethanol-acetic acid mixture without using any complexing aid (e.g., polyol or polyhydroxy acid, etc.), which is essentially used in the polymeric precursor routes. This modification minimises the organic contamination in the resulting ceramic that is formed as single perovskite at 650°C, after short calcination time periods. The formation of a monophasic material and absence of second phases or phase segregation was confirmed by powder X-ray diffraction, energy dispersive X-ray and electron microscopy of the ceramic calcined at higher temperatures (800–1400°C). The calcined samples are nanocrystalline up to 1000°C (average particle size, ∼44 nm) however, significant particle growth is observed at higher temperatures with micron-sized grains present in the sample sintered at 1400°C. The sample exhibits the characteristic colossal magnetoresistance behaviour. Owing to the high chemical and structural purity of the obtained ceramic, the intrinsic bulk features like metal-insulator transition and ferromagnet-antiferromagnet behaviour of the polycrystalline sample are comparable to those observed in the single crystal La2/3Ca1/3MnO3 specimen, used as a reference. The single-crystal-like properties are also corroborated by the observation of a sharp metallic fermi edge in the UPS measurements. The variable temperature photoemission spectra reveal a temperature dependent redistribution of spectral weight close to the fermi level corroborating the temperature dependent resistance and magnetoresistance of the sample. The material shows a homogeneous grain size and a high sinterability as shown by TEM and SEM studies, respectively. XPS study indicates a charge carrier hopping between Mn3+(3d4) and Mn4+(3d3) sites. [ABSTRACT FROM AUTHOR]

Advances in thin film deposition techniques, in particular molecular beam epitaxy, have made it possible to produce bilayer heterostructures of high-temperature superconductors and manganite perovskites. The latter exhibit the phenomenon of colossal magnetoresistance (CMR). The half-metallic character of CMR compounds results in their carriers being spin polarized. The geometry of the structures that have been fabricated is such that it is possible to measure the interface conductance–voltage characteristic G(V) as well as the current–voltage characteristic of the superconducting half of the bilayer. Injection of carriers suppresses superconductivity in the latter, with a current gain of order unity. The data exhibit qualitative features of equilibrium theories of spin-polarized transport across an interface between a ferromagnet and an anisotropic superconductor, although a detailed understanding requires generalization of the theory to include out of equilibrium effects. [ABSTRACT FROM AUTHOR]

A survey is given of NMR studies of colossal magnetoresistive manganese perovskites (RE,Ca,Sr,Ba)MnO3 (RE = rare earth) and the interstitially modified permanent magnet materials, RE2Fe17A x (A = N, C, H) at ambient pressure and at applied pressures of up to 10 kbar. The different pressure behavior of the Mn hyperfine field found in the metallic and in the insulating manganite compounds is discussed and related to the micro- and macroscopic properties of these magnetically inhomogeneous materials. In the RE2Fe17A x compounds a different pressure behavior of the hyperfine field at the RE sites with different number and type of interstitial atom neighbors is discussed in terms of local compressibility. The influence of the interstitial modification and the applied pressure on the RE hyperfine field and quadrupole splitting is analyzed and the impact of the “chemical pressure” and covalent effects on these quantities is compared. A comparison of the behavior of the magnetic state of the 4f electron shell with pressure and with interstitial modification is made and the relation to the magnetocrystalline anisotropy is discussed. [ABSTRACT FROM AUTHOR]

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 111 mCd 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. [ABSTRACT FROM AUTHOR]

The ferromagnetic transition temperatures have been measured on two bathes of perovskite manganese oxides such as (La1- x R x )2/3Ca1/3MnO3(R=Ce, Pr, Nd, etc.) and La2/3(Ca1- y Cd y )1/3MnO3. It is found that the (La1- x R x )2/3Ca1/3MnO3 samples have obviously different Curie temperature T C although their (rA) (the average A-site cation radius) are almost identical, and the T C in the system of (La1- x R x )2/3Ca1/3MnO3(R=Ce, Pr, Nd, etc.) and La2/3(Ca1- y Cd y )1/3MnO3. It is found that the (La1- x R x )2/3Ca1/3MnO3 compounds increases with increasing y although (rA) decreases slightly. It is suggested that the Curie temperature should be influenced by the average local A-site magnetic moment in the ferromagnetic perovskite manganite system. [ABSTRACT FROM AUTHOR]

The magnetic behavior of the distorted perovskite manganese, Pr0.65Ca0.35MnO3 was studied by X-band electron spin resonance for powder samples. We observed the onset of the charge-ordered state at TCO∼215 K, the antiferromagnetic transition with the peak of the ESR linewidth, ΔH p−p at TAF∼180 K and the canted antiferromagnetic transition at TCAF∼125 K associated with the abrupt increase of both the effective magnetization and ΔH p−p. Below 90 K, the absorption intensity profile becomes weakened with decreasing temperature suggesting the existence of some kind of magnetic disorder below 90 K, which is responsible for a part of evidence of the existence of the spin-glass state as has been proposed by Yoshizawa et al., Phys. Rev. B 52, 1689 (1996). [ABSTRACT FROM AUTHOR]

Electron-spin resonance (ESR) for the charge-ordered state in well-characterized Pr0.65Ca0.35MnO3 exhibited significant change of both the absorption profile and the effective spin susceptibility upon injection of laser light with photon energy of 1.17 eV provided by Nd-YAG laser. The increase of the effective spin susceptibility was clearly found out thanks to the injection of photons in the temperature range 90 K–80 K, which is below the transition temperature from the antiferromagnetic charge ordered state to the canted antiferromagnetic spin alternation state, TCAF∼125 K. The temperature dependence of the change of the ESR profile excludes the possibility of heating by laser light. The present result suggests that a kind of photo-induced insulator–metal transition may occur due to propagation of the delocalized carriers via probable double exchange interaction in the charge-ordering collapsed state created by the injection of photons. [ABSTRACT FROM AUTHOR]