Perovskite Manganite Oxides Research Articles

Microwave-aided fabrication of calcium-substituted DyMnO3 nanocomposites as prospective battery-type electrode material for supercapacitors

The Multifaceted properties of nanostructured rare earth perovskite manganite oxides have attracted much attention specifically for their applications in energy storage systems. In the present work, synthesis and physiochemical properties of calcium-substituted dysprosium perovskite manganite oxide nanocomposites and their potential applications as supercapacitors are examined. The perovskite structure and morphology of the designed nanocomposites are affirmed by the different analytical tools, including XRD, SEM, and TEM analysis. The structural analysis by XRD indicates the presence of DyMnO3 perovskite phase with additional peaks of Dy2O3 phase. The percentage of Dy2O3 is gradually reduced with higher Ca substitution, from about 16% to 7%. The Halder-Wagner method indicates an increase of the microstrain and a decrease in crystallite size with the rise of Ca substitution. From Tauc’s plot derived from DRS analysis, a slight increase in the band gap with the increase in Ca substitution is observed (2.55–2.62 eV). The surface elemental compositions and the valence states of individual elements analyzed using XPS analysis evidence the presence of Dy, Ca, Mn, and O. BET adsorption study indicates an increase in pore size, surface area, and pore volume with increasing Ca substitution concentration. When employed as a supercapacitor electrode material, Calcium-blend DyMnO3 nanocompositeexhibits battery type behavior. This material shows a higher specific capacitance (capacity) of 531 Fg−1 (319.9 Cg−1) with comparatively low charge transfer resistance and better cyclic stability. We have assembled an asymmetric supercapacitor device using our prepared sample exhibiting energy density of 36.16 Wh/kg with better cyclic stability. This work provides new insights for designing future Dy2O3 based supercapacitors.

Flexible La0.67Sr0.33MnO3:ZnO Nanocomposite Thin Films Integrated on Mica

The integration of functional oxide thin films on flexible substrates is critical for their application in flexible electronics. Here, to achieve flexible perovskite manganite oxide film with excellent low-field magnetoresistance (LFMR) effect, textured La0.67Sr0.33MnO3 (LSMO):ZnO nanocomposite film was deposited on a flexible mica substrate with ZnO buffer using pulsed laser deposition (PLD). Compared to the polycrystalline LSMO:ZnO nanocomposite film directly deposited on mica without buffer, the LSMO:ZnO/ZnO/mica sample exhibits larger saturation magnetization (164 emu/cm3) and higher Curie temperature (∼319 K), which results from the crystallinity and strain in the LSMO phase. In addition, the LSMO:ZnO/ZnO/mica film presents a high MR value of ∼39% at 10 K under 1 T. Furthermore, the good mechanical stretchability and property stability of the nanocomposite thin films have been demonstrated with mechanical bending.

Thermal relaxation in a disordered one-dimensional array of interacting magnetic nanoparticles

We consider a system of single-domain magnetic nanoparticles placed along a linear chain and address the effect of the distance between them on the magnetic and thermal relaxation properties of the system. The nanoparticles interact with each other through the dipolar interaction and we introduce disorder into the system by allowing random sizes of the nanoparticles and random directions of their uniaxial anisotropy axes. In particular, the radius of the spherical nanoparticles are drawn from a log-normal distribution. The dynamical behavior of the magnetic moments of the system is studied through numerical simulations of the stochastic Landau-Lifshitz-Gilbert equation, taking into account explicit temperature dependence of the saturation magnetization and uniaxial anisotropy energy density to describe the magnetic properties of perovskite manganite oxide nanoparticles. Hysteresis, zero-field-cooled and field-cooled curves are measured, from which we can find the coercive field and the blocking temperature as a function of the magnitude of the dipolar coupling, controlled by the distance between the particles. We show that both the coercive field and blocking temperature decrease as a function of the separation between the nanoparticles. The magnetic relaxation is measured as a function of both temperature and time, from which we estimate the effective energy barrier distribution of the system. We show that the peak of the energy barrier distribution moves to lower energies as the separation between neighboring particles increases, or equivalently, as the dipolar interaction is reduced.

Effect of A-site deficiency on the structural and magnetic properties of La0.8−x□xNa0.2−x□xMnO3 oxides and estimation of the magnetocaloric behavior

The morphological, structural, magnetic and magnetocaloric properties of perovskite manganite oxides La0.8−x□xNa0.2−x□xMnO3 are studied with x = 0 and 0.1. The X-ray diffraction (XRD) data were analyzed by Rietveld refinement technique which reveals that the samples crystallized in a rhombohedral structure with R3¯c space group. As for the magnetic measurements, it is found that the two samples undergo a transition from the ferromagnetic state (FM) to paramagnetic state (PM) with the increase of temperature. The transition temperature, called the Curie temperature (TC), decreases from 324 K for the parent compound (x = 0) to the range of room temperature (304 K) for x = 0.1. Moreover, from magnetization measurements versus magnetic applied field, we studied the magnetocaloric effect (MCE) by the determination of the magnetic entropy change ΔSM. The maximum magnetic entropy changes ΔSMMax increases from 2.91 J/kg.K for x = 0–3.23 J/kg.K for x = 0.1 under an applied magnetic field of 2 T. The Relative Cooling Power (RCP) values were found to reach 76.13 J/K and 70.36 J/K for x = 0 and 0.1, respectively, for the same applied magnetic field (μ0H = 2 T). Thanks to the mentioned values obtained around the Curie temperatures, these materials are suggested to be good candidates as magnetic refrigerants for magnetic refrigeration in the above-room and room temperature range. Besides, a mixture of these two materials may form a composite refrigerant working in a larger temperature range limited by their TC.

Micromagnetic simulation study of a disordered model for one-dimensional granular perovskite manganite oxide nanostructures

Chemical techniques are an efficient method to synthesize one-dimensional perovskite manganite oxide nanostructures with a granular morphology, that is, formed by arrays of monodomain magnetic nanoparticles. Integrating the stochastic Landau-Lifshitz-Gilbert equation, we simulate the dynamics of a simple disordered model for such materials that only takes into account the morphological characteristics of their nanograins. We show that it is possible to describe reasonably well experimental hysteresis loops reported in the literature for single La_0.67Ca_0.33MnO_3 nanotubes and powders of these nanostructures, simulating small systems consisting of only 100 nanoparticles.

Study of the Effects of A‐Site La‐Substition on the Electrical and Magnetic Properties of Dy0.5Sr0.5MnO3 Ceramics

The Dy0.5−xLaxSr0.5MnO3 (0 ≤ x ≤ 0.4) manganite compounds have been synthesized by solid state reaction, and the effect of nonmagnetic La ion doping on the crystal structure, electrical and magnetic properties are systematically investigated. It is found that with successive substitution of La element, A‐site cationic arrangement transforms from disorder (random, x ≤ 0.25) to order structure (x > 0.25), and the crystal structure undergoes a transition from cubic to orthogonal distorted perovskite structure. When 0 ≤ x < 0.25, the compounds show a similar semiconducting behavior and magnetic property with a low‐temperature spin‐glass state. When x = 0.25, however, long‐range ferromagnetic (FM) order begins to form and coexists with anti‐ferromagnetic (AFM) phase in the compound. When x further increases, FM interactions strengthen and become predominant in the magnetic properties of the compound. On the other hand, in contrast to the semiconducting behavior of the compounds with x ≤ 0.25, when x > 0.25, the resistivity decreases quickly in the corresponding temperature range. It is suggested that not only the A‐site cationic disorder turning, closely related to the cation radius distribution (mismatch), σ2, controlled by A‐site cation radius 〈rA〉, but the substitution of nonmagnetic La ions, or A‐site magnetic change, is an effective way to adjust the crystal structure and the related magnetic and electrical properties of the perovskite manganite oxides for the applications.

Large magnetocaloric effect and critical behavior in La0.7Ba0.2Ca0.1Mn1−xAlxO3

The structural, magnetic and magnetocaloric properties of La0.7Ba0.2Ca0.1Mn1−xAlxO3 (0 ≤ x ≤ 0.1) perovskite manganite oxides have been investigated.

One-Dimensional Perovskite Manganite Oxide Nanostructures: Recent Developments in Synthesis, Characterization, Transport Properties, and Applications.

One-dimensional nanostructures, including nanowires, nanorods, nanotubes, nanofibers, and nanobelts, have promising applications in mesoscopic physics and nanoscale devices. In contrast to other nanostructures, one-dimensional nanostructures can provide unique advantages in investigating the size and dimensionality dependence of the materials’ physical properties, such as electrical, thermal, and mechanical performances, and in constructing nanoscale electronic and optoelectronic devices. Among the one-dimensional nanostructures, one-dimensional perovskite manganite nanostructures have been received much attention due to their unusual electron transport and magnetic properties, which are indispensable for the applications in microelectronic, magnetic, and spintronic devices. In the past two decades, much effort has been made to synthesize and characterize one-dimensional perovskite manganite nanostructures in the forms of nanorods, nanowires, nanotubes, and nanobelts. Various physical and chemical deposition techniques and growth mechanisms are explored and developed to control the morphology, identical shape, uniform size, crystalline structure, defects, and homogenous stoichiometry of the one-dimensional perovskite manganite nanostructures. This article provides a comprehensive review of the state-of-the-art research activities that focus on the rational synthesis, structural characterization, fundamental properties, and unique applications of one-dimensional perovskite manganite nanostructures in nanotechnology. It begins with the rational synthesis of one-dimensional perovskite manganite nanostructures and then summarizes their structural characterizations. Fundamental physical properties of one-dimensional perovskite manganite nanostructures are also highlighted, and a range of unique applications in information storages, field-effect transistors, and spintronic devices are discussed. Finally, we conclude this review with some perspectives/outlook and future researches in these fields.

Rectifying behavior and photovoltage effect in La1.3Sr1.7Mn2O7/SrTiO3-Nb heterostructure

Perovskite oxide heterostructure possesses attractive magnetic, optical and electric properties, such as superconducting interface between two insulators, two-dimensional electron gas, positive giant magnetoresistance, photoelectric response characteristic, magnetocaloric effect, and coexistent different magnetic structures. Especially for the photoelectric response behaviors of A1-xAxMnO3 (A=La, Pr etc.; A = Sr, Ca etc.) perovskite manganese oxide heterostructure, one has made a systematic study on the photoelectric conversion efficiency, the photovoltaic response speed, and the in-plane lateral photovoltage. Besides A1-xAxMnO3 structure, manganese oxides can also exhibit the double layered perovskite structure A2-2xA1+2xMn2O7. Double layered perovskite structure can be regarded as the layers of perovskite and rock salt which are alternately stacked. This double layered perovskite manganese oxide (such as La2-2xSr1+2xMn2O7) is a natural structure of the tunnel structure: ferromagnetic metal layer-insulating layer-ferromagnetic metal layer. Double layered perovskite manganese oxide has not only the characteristics of giant magnetoresistance, but also the novel physical properties, such as persistent photoconductivity, etc. However, there are few reports on the physical properties of the double layered perovskite manganite oxides, heterostructures, especially the photovoltaic properties. In this work, the La1.3Sr1.7Mn2O7 (LSMO) film is deposited on an n-type SrTiO3-Nb (NSTO) single crystal substrate by a pulsed laser deposition method. Additionally, we study the transporting properties of LSMO/NSTO heterostructure and its photovoltaic effect. The heterostructure exhibits benign rectifying and palpable photovoltaic effect. Under the 532 nm laser irradiation, the photovoltage first increases and then decreases with temperature rising. The maximal photovoltage reaches 400 mV at 150 K which is consistent with the metal-insulator transition temperature of LSMO film. It is indicated that the photovoltaic effect of the heterostructure is regulated by the inner transporting characteristics of LSMO film. The dynamical process of the heterostructure, photovoltaic response, is analyzed. Meanwhile, by analyzing the relationship between the photovoltage and time, it is found that the rising edge fits to the first order exponential function, which is related to the migration of carriers. While the falling edge of second-order exponential function indicates that the compound of carriers has two different physical processes: 1 corresponds to the neutralization process of the carriers aggregated on both junction sides through the external circuit, and 2 corresponds to the annihilation process of non-equilibrium carriers. The carrier lifetime of our p-n junction is longer, on the order of ms, than those of other manganese oxides p-n junctions. Remarkably, the time constants of both the rising edge and falling edge first increase and then decrease as temperature increases, and the maximum values occur at the metal-insulator transition temperature of LSMO film.

Photoelectric detecting properties of perovskite manganite and their application in the petroleum fields

The traditional optical sensors cannot meet the demand in the harsh environment as the scope of oil exploration become deeper and deeper. New types of photoelectric detectors which can work in the high temperature and pressure environment and also have high performances in photoelectric sensitivity and responsivity are of great significance. This paper summarize our recent advances of photoelectric detectors based on perovskite manganite oxides working in at high temperature. We fabricated photoelectric detector structures by deposited manganite films on different substrates. We systemically study the properties of the detector and enhance the photovoltaic sensitivity by various ways. We also focus on the photoelectric properties with the temperature increasing to 500 degree centigrade and find that the tilted manganite film shows stability of photovoltaic response at the high temperature. These results not only help to reveal the physical mechanism of the electron strong correlation system, but also show an attractive potential application in petroleum exploration and oil wells security fields.

Band Structure Analysis of La0.7Sr0.3MnO3Perovskite Manganite Using a Synchrotron

Oxide semiconductors and their application in next-generation devices have received a great deal of attention due to their various optical, electric, and magnetic properties. For various applications, an understanding of these properties and their mechanisms is also very important. Various characteristics of these oxides originate from the band structure. In this study, we introduce a band structure analysis technique using a soft X-ray energy source to study aLa0.7Sr0.3MnO3(LSMO) oxide semiconductor. The band structure is formed by a valence band, conduction band, band gap, work function, and electron affinity. These can be determined from secondary electron cut-off, valence band spectrum, O 1s core electron, and O K-edge measurements using synchrotron radiation. A detailed analysis of the band structure of the LSMO perovskite manganite oxide semiconductor thin film was established using these techniques.

A-site-deficiency-dependent structural, magnetic and magnetoresistance properties in the Pr0.6Sr0.4MnO3 manganites

Structural, magnetic and magneto-transport properties of Pr0.6Sr0.4MnO3, Pr0.6Sr0.3□0.1MnO3 and Pr0.5□0.1Sr0.4MnO3 perovskite manganite oxides have been investigated. X-ray diffraction (XRD) analysis using Rietveld refinement has shown that all the samples under investigation crystallize in the orthorhombic structure with Pbnm space group. Strontium vacancy leads to an increase in the unit cell volume. Paramagnetic (PM) to ferromagnetic (FM) transitions have been observed in all the synthesized samples. The Curie temperature was found to be 251K for the strontium-deficient sample, 273K for the stoichiometric sample and 275K for the praseodymium-deficient one. With the decrease in temperature, the two deficient samples exhibit semiconducting–metallic transitions. The resistivity decreases while Tρ increases with the change in the magnetic applied field from 0T to 5T. The strontium-vacancy sample has been proven to exhibit a magnetoresistance value of about 50% at 266K at a magnetic applied field of 5T and seems to be constant below 236K. The praseodymium-deficient one is manifested in another form of MR which increases with the decrease in temperature. This is a clear indication of the low field magnétoresistance (LFMR) behavior.

Research progress on electronic phase separation in low-dimensional perovskite manganite nanostructures.

Perovskite oxide manganites with a general formula of R1-x AxMnO3 (where R is a trivalent rare-earth element such as La, Pr, Sm, and A is a divalent alkaline-earth element such as Ca, Sr, and Ba) have received much attention due to their unusual electron-transport and magnetic properties, which are indispensable for applications in microelectronic, magnetic, and spintronic devices. Recent advances in the science and technology have resulted in the feature sizes of microelectronic devices based on perovskite manganite oxides down-scaling into nanoscale dimensions. At the nanoscale, low-dimensional perovskite manganite oxide nanostructures display novel physical properties that are different from their bulk and film counterparts. Recently, there is strong experimental evidence to indicate that the low-dimensional perovskite manganite oxide nanostructures are electronically inhomogeneous, consisting of different spatial regions with different electronic orders, a phenomenon that is named as electronic phase separation (EPS). As the geometry sizes of the low-dimensional manganite nanostructures are reduced to the characteristic EPS length scale (typically several tens of nanometers in manganites), the EPS is expected to be strongly modulated, leading to quite dramatic changes in functionality and more emergent phenomena. Therefore, reduced dimensionality opens a door to the new functionalities in perovskite manganite oxides and offers a way to gain new insight into the nature of EPS. During the past few years, much progress has been made in understanding the physical nature of the EPS in low-dimensional perovskite manganite nanostructures both from experimentalists and theorists, which have a profound impact on the oxide nanoelectronics. This nanoreview covers the research progresses of the EPS in low-dimensional perovskite manganite nanostructures such as nanoparticles, nanowires/nanotubes, and nanostructured films and/or patterns. The possible physical origins of the EPS are also discussed from the signatures of electronic inhomogeneities as well as some theoretical scenarios, to shed light on understanding this phenomenon. Finally, the perspectives to the future researches in this area are also outlined.

Griffiths Phase and Disorder in Perovskite Manganite Oxides La1−x Ca x MnO3 and La0.7Sr0.3MnO3

Polycrystalline samples La1−x Ca x MnO3 (x=0.17, 0.15, 0.10) and La0.7Sr0.3MnO3 were prepared in order to investigate the Griffiths-like features induced by disorder compared with their counterpart single crystals. The magnetization data exhibit the traditional transition from ferromagnetic phase to paramagnetic phase. From the temperature dependence of inverse susceptibility, it can be testified that the Griffiths-like features still exist in as-prepared Ca doped samples, while non-Griffiths-like features exist in La0.7Sr0.3MnO3. All these samples, however, exhibit the large effective spins resulting from formation of the short-order ferromagnetic clusters. The O K-edge X-ray absorption spectra indicate the Jahn–Teller (J-T) distortions are definitely present due to the J-T ion Mn3+, which indicate that static J-T distortion is not a sufficient condition for the existence of Griffiths phase in Sr-doped system. And, the size of J-T distortion is a little larger in polycrystalline La0.7Sr0.3MnO3 than that in polycrystalline samples La1−x Ca x MnO3 (x=0.17, 0.15, 0.10), revealed by X-ray diffraction parameters and extended X-ray fine structure absorption data of Mn K-edge. It also testifies that the disorder in La0.7Sr0.3MnO3 caused by both chemical doping and J-T distortions is lower than that in polycrystalline samples La1−x Ca x MnO3, which may be the reason of non-Griffiths-like phase existing in La0.7Sr0.3MnO3 samples.

Magnetic interaction at an interface between manganite and other transition metal oxides

A general consideration is presented for the magnetic interaction at an interface between a perovskite manganite and other transition metal oxides. The latter is specified by the electron number $n$ in the $d_{3z^2-r^2}$ level as $(d_{3z^2-r^2})^n$. Based on the molecular orbitals formed at the interface and the generalized Hund's rule, the sign of the magnetic interaction is rather uniquely determined. The exception is when the $d_{3z^2-r^2}$ orbital is stabilized in the interfacial manganite layer neighboring to a $(d_{3z^2-r^2})^1$ or $(d_{3z^2-r^2})^2$ system. In this case, the magnetic interaction is sensitive to the occupancy of the Mn $d_{3z^2-r2}$ orbital. It is also shown that the magnetic interaction between the interfacial Mn layer and the bulk region can be changed. Manganite-based heterostructures thus show a rich magnetic behavior. We also present how to generalize the argument including $t_{2g}$ orbitals.

Field Effects in Thin Films of Manganites Using a Planar Field Effect Configuration

Modulation of the metal-insulator phase transition of perovskite manganite oxides is achieved by a static electric field. The field is applied using a planar field-effect configuration, which was formed on a monolayer film. In such a field-effect configuration, La1−xAxMnO3 film is used as the channel and substrate acts as the gate. Both divalence-doped (La0.7Ba0.3MnO3, Pr0.7Sr0.3MnO3), and tetravalence-doped (La0.7Ce0.3MnO3) systems demonstrate significant field effects. The field modulations are found being nonlinear and polarity dependent on the applied bias. The results obtained in La0.7Ce0.3MnO3 indicates that electron doped manganites have similar features as those found in hole doped manganites. The observed field effects were discussed with the percolative phase separation picture.

Preparation and Properties of Novel Bonded Perovskite Manganite Oxides

The two-phase perovskite manganese composites have potential application in the field of spintronics, as the observed enhanced low-field magnetoresistance in this kind of composite. To prepare the real manganite-based two-phase composition, the concept of bonded perovskite manganese was put forward recently. In this article we review main research results in these bonded perovskite manganite oxide composites and give some expectation.

Magnon-polaron and spin-polaron signatures in the specific heat and electrical resistivity ofLa0.6Y0.1Ca0.3MnO3in zero magnetic field and the effect ofMn—O—Mnbond environment

$La_{0.6}Y_{0.1}Ca_{0.3}MnO_{3}$, an $ABO_{3}$ perovskite manganite oxide, exhibits a non trivial behavior in the vicinity of the sharp peak found in the resistivity $\rho$ as a function of temperature $T$ in zero magnetic field. The various features seen on $d\rho/dT$ are discussed in terms of competing phase transitions. They are related to the $Mn-O-Mn$ bond environment depending on the content of the $A$ crystallographic site. A Ginzburg-Landau type theory is presented for incorporating concurrent phase transitions. The specific heat $C$ of such a compound is also examined from 50 till 200 K. A log-log analysis indicates different regimes. In the low temperature conducting ferromagnetic phase, a collective magnon signature ($C \simeq T^{3/2}$) is found as for what are called magnon-polaron excitations. A $C \simeq T^{2/3}$ law is found at high temperature and discussed in terms of the fractal dimension of the conducting network of the weakly conducting (so-called insulating) phase and Orbach estimate of the excitation spectral behaviors. The need of considering both independent spin scattering and collective spin scattering is thus emphasized. The report indicates a remarkable agreement for the Fisher-Langer formula, i.e. $C$ $\sim$ $d\rho/dT$ at second order phase transitions. Within the Attfield model, we find an inverse square root relationship between the critical temperature(s) and the total local $Mn-O-Mn$ strain.

Neutron diffraction, structural and magnetic properties of (La 1− yPr y) 0.9Na 0.1MnO 3

A systematic study of the structural and magnetic properties of the diluted perovskite manganite oxides (La 1− y Pr y ) 0.9Na 0.1MnO 3 (0.2≤ y≤0.8) had been carried on. In this study, the average ionic radius 〈 r A〉 of the A cation site was systematically varied while keeping fixed the carrier concentration (Mn 3+/Mn 4+ ratio). X-Ray diffraction investigations showed a structural transition from the rhombohedral to the orthorhombic system for 0.33≤ y≤0.5. The unit cell volume decreases with increasing Pr 3+ content. Magnetic measurements showed that our synthesized samples exhibit a paramagnetic to ferromagnetic transition with decreasing temperature. Neutron diffraction studies show that (La 0.2Pr 0.8) 0.9Na 0.1MnO 3 powder sample crystallizes in the orthorhombic system with Pnma space group at room temperature and at 10 K. The magnetic moment of Pr and Mn atoms are coupled parallel to the b-axis.

Ferromagnetism in the lacunar (Pr, Sr)MnO 3 perovskite manganites

Structural, magnetic and magneto-transport properties in the defect Pr 0.7− x □ x Sr 0.3MnO 3 (0⩽ x⩽0.23) and Pr 0.7Sr 0.3− x □ x MnO 3 (0⩽ x⩽0.3) perovskite manganite oxides have been investigated. Our samples have been elaborated by the conventional ceramic method. Structural analysis shows that all samples have a perovskite structure with different distortion degrees. X-ray diffraction patterns show that our samples are in a single phase. Strontium-deficient samples crystallized in a rhombohedral structure with R 3 ̄ c space group for 0⩽ x⩽0.2 and in the orthorhombic symmetry with Pbnm space group for x>0.2; while in the praseodymium-deficient samples, the rhombohedral to orthorhombic transition occurs for x>0.1. All the praseodymium-deficient samples exhibit a paramagnetic–ferromagnetic transition when the temperature decreases while the strontium-deficient ones exhibit such transition only for low x values. The magnetic transition temperature shifts to lower values as the strontium deficiency increases and to higher values with the praseodymium-deficient increase. With decreasing temperature, all the praseodymium-deficient samples exhibit a semiconducting-metallic transition, while such transition is observed only for low x values (0⩽ x⩽0.1) in the strontium-deficient ones. At a magnetic applied field of 2 T, stoichiometric sample Pr 0.7Sr 0.3MnO 3 exhibits a magnetoresistance (MR) effect of about 60% at 265 K. For the strontium-deficient samples ( x=0.05 and x=0.1), the MR at a magnetic applied field of 2 T is found to be about 90% for Pr 0.7Sr 0.25□ 0.05MnO 3 and 70% for Pr 0.7Sr 0.2□ 0.1MnO 3. For the praseodymium-deficient sample ( x=0.1), the MR remains constant below T ρ =250 K at a value of about 20–25% for H=2 T.