Добірка наукової літератури з теми "Doped Perovskite Manganites"

Perovskite manganites have been the focus of worldwide research during the last two decades because of the observation of colossal magnetoresistance (CMR) effect. These materials have potential applications in magnetic field sensors, spin filters, infrared bolometers and cathodes for solid oxide fuel cells. Such manganites are also important from the fundamental study viewpoint as they offer interplay among various degrees of freedom viz. spin, lattice and charge ordering. Moreover, phase separation may occur in manganites with low concentration of the dopant. In such scenario, ferromagnetic metallic clusters are embedded in antiferromagnetic insulating matrix. The fraction of these magnetic phases may vary from the nano- to micro-scale. With higher dopant concentration, the percolation of these magnetic metallic clusters leads to the apparent CMR effect. In this study we focus our attention to the low doped La0.8Sr0.2MnO3 (LSMO) manganite and investigate the possible magnetic phase separation and effect of variation in grain size on the magnetic domain size. La0.8Sr0.2MnO3 possesses Curie temperature (TC) higher than room temperature, therefore the material is supposed to be in the magnetic state at room temperature.

The Systematic investigation of structural behaviour of GdMn1-xCrxO3 (x=0, 0.1, 0.2) has been undertaken which are synthesized by conventional solid state reaction method. All the XRD reflection lines were successfully indexed according to orthorhombic perovskite structure with space group: pbnm (62). Upon chromium (Cr) doping on the Mn site the unit cell volume has reduced due to slight difference between the ionic radii of Cr 3+ and Mn 3+ compare with Pure GdMnO 3. The relation between lattice parameter infer that all the samples have O´ type orthorhombic structure which is highly distorted perovskite structure but increasing the Cr concentration the orthorhombic distortion decrease that deduce the non John Teller nature of these samples.

In this work attempts to prepare strontium-doped lanthanum manganites La1-xSrxMnO3 using microwave-assisted hydrothermal synthesis were undertaken from a mixture of lanthanum nitrate, strontium nitrate, manganese(II) nitrate, potassium permanganate and potassium hydroxide as a mineralizer. For x = 0.3, and x = 0.5, the perovskite obtained is not defined since both La0.7Sr0.3MnO3 and La0.5Sr0.5MnO3 phases are consistent with XRD spectra. While with x = 1.0, for the first time, hexagonal strontium manganite was prepared as blade-shaped crystallites with a narrow particle length distribution (range 3.75-7.75 μm) at 210°C using a treatment time of only 1 hour. Conventional hydrothermal synthetic routes require at least 24 hrs treatment time.

The electronic structure of the perovskite manganites LaMnO3 and La2/3 Al1/3 MnO3 was presented. The calculations were made within density functional theory (DFT) and PBE exchange correlations energy approximation. It was found that inclusion of Al dopants add additional states near the Fermi level and decreasing the resistivity values for all temperature range.

In this work the advantage of the use of the microwave technology was exploited for the preparation of perovskite ceramics. Microwave-assisted hydrothermal method has been applied to the preparation of strontium-doped lanthanum manganites with different stoichiometric ratio of the three oxides, La1-x SrxMnO3 (x = 0.3, 0.5, 0.6). In particular, pure black narrow dispersed crystallites of La0.5Sr0.5MnO3 of 0.68?0.18 ?m were prepared in only 45 minutes at 240?C and a KOH concentration of 21 M. The complete chemical, mineralogical and microstructural characterization of the powders reveal the same structural properties of the perovskite powders previously synthesised by ceramic and conventional hydrothermal routes. .

Intensive research interests in condensed matter physics have been focused at the strongly correlated electron systems. Most of the efforts were devoted in hole-doped manganites with a double exchange interaction between Mn3+/Mn4+. Recently, tetravalent ions substitution has also stimuli much attention as a supplement for the hole-doping. Such electron-doped manganites may be of great potential for the development of all-manganites devices. Manganites are extremely sensitive to external disturbances, such as magnetic fields, electric fields, currents, mechanical strain, and photo illumination, etc. These extraordinary properties make manganites promising for practical applications. In this thesis, the field modulation on physical properties in electron/hole-doped manganites films and heterojunctions were investigated. The effects of tetravalent hafnium doping on the structural, transport, and magnetic properties of polycrystalline La1-xHfxMnO3(LHMO) (0.05 ≤x ≤0.3) were studied systematically. A phase diagram was obtained for the first time through magnetization and resistance measurements in a broad temperature range. An abnormal enhancement of magnetization was observed at about 42 K. It was further confirmed that the second magnetic phase MnO2in LHMO gives rise to such a phenomenon. The dynamic magnetic properties of LHMO, such as relaxation and aging processes, were studied, demonstrating a spin-glass state at low temperature accompanied by a ferromagnetic phase. Heterojunctions composed of n-type SrTiO3-δand p-type GaAs exhibited excellent rectifying behavior from 40K to room temperature. The photocarrier injection effect and a colossal photo-resistance were observed. Strong dependences on both temperature and bias voltage were found as well, which might be under stood by considering the band structure of the formed p-njunction. By employing an ultrathin SrTiO3buffer layer,La0.8Ca0.2MnO3films could be epitaxially grown on GaAs substrates. The heterostructures exhibit good rectifying behavior with a paramagnetic-ferromagnetic transition at ~200K. The variation of diffusion voltage with temperature in these heterostructures could be explained by the effects of the Hund’s rule coupling between the La0.8Ca0.2MnO3and the buffer layer. The effects of the strain induced by ferroelectric poling on the magnetic and electric properties have been investigated by using 0.67Pb(Mg1/3Nb2/3)O3-0.33PbTiO3(PMN-PT) substrates. The polarization of the PMN-PT crystal reduces the biaxial tensile strain in the formed La0.9Hf0.1MnO3layer.It results in a significant decrease in resistance and an enhancement of the phase transition temperature as well as the magnetization. The impact of the lattice strain on the charge/orbital ordering state was also been studied. The modification of charge/orbital ordering phase by the electric fields and ferroelectric polarization suggested that the unstable states in the manganites are sensitive to the strain. Heterojunctions of La1-xHfxMnO3/Nb:SrTiO3 were fabricated and investigated under different fields (electric, magnetic and optic). These heterojunctions exhibited excellent rectifying behavior in a wide temperature range. Their properties could be significantly modulated by magnetic fields. Prominent photovoltaic effect was also observed in the formed junctions.
published_or_final_version
Physics
Doctoral
Doctor of Philosophy

The development of more advanced materials forms the basis of technological progress. One group of fascinating compounds with many potential applications in spintronic devices are the mixed-valence perovskite manganites. These have attracted considerable interest during the last decade through their very large magnetoresistance near the Curie Temperature. Although the properties of a material determinie any application, the development of reliable and flexible synthesis methods is crucial, as is the understanding of these methods. Knowledge of how different materials are formed is also of general importance in tailoring new materials. The aim of this project has therefore been not only to develop a new synthesis route, but also to understand the mechanisms involved.

This thesis describes the synthesis and characterization of a novel manganese alkoxide and its use in sol–gel processing of magnetoresistive perovskite manganites. In searching for a soluble manganese alkoxide for sol–gel processing, we found that the methoxy-ethoxide, [Mn₁₉O₁₂(moe)₁₄(moeH)₁₀]·moeH, has a high solubility in appropriate organic solvents. Being 1.65 nm across, it is one of the largest alkoxides reported; it is also of interest because of its (for oxo-alkoxides) rare planar structure. After mixing with La, Nd, Ca, Sr, and Ba methoxy-ethoxides, [Mn₁₉O₁₂(moe)₁₄(moeH)₁₀]·moeH was used in the first purely alkoxide based sol–gel processing of perovskites manganites. The phase evolution on heating xerogel powders to 1000°C was studied, and thin films were prepared by spin-coating.

It was found that the easily oxidised Mn-alkoxide facilitates the formation of high oxygen-excess modifications of the perovskites. The reactive precursor system yields fully hydrolysed gels almost without organic residues, but the gel absorbs CO₂ from the air, leading to carbonate formation. The carbonate decomposition is the limiting step in oxide formation. Transport measurements of La_0.67Ca_0.33MnO₃ films on LaAlO₃ substrate show that all-alkoxide sol–gel derived films can compete with PLD films in terms of quality of epitaxy and transport. The somewhat different behaviour of the sol–gel derived films compared to PLD films is attributed to differences in morphology and oxygen stoichiometry.

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Dissertação (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Lai Chun Hei Gary = 錳氧化物-鈮摻雜之鈦酸鍶異構結的輸運特性 / 黎鎮禧.
Thesis (M.Phil.)--Chinese University of Hong Kong, 2005.
Includes bibliographical references.
Text in English; abstracts in English and Chinese.
Lai Chun Hei Gary = Meng yang hua wu-ni shan za zhi tai suan si yi gou jie de shu yun te xing / Li Zhenxi.
Acknowledgement --- p.i
Abstract --- p.ii
論文摘要 --- p.iv
Table of contents --- p.vi
List of Figures --- p.x
List of Tables --- p.xv
Chapter Chapter 1 --- Introduction
Chapter 1.1 --- Introduction to perovskite manganites and niobium doped strontium titanate --- p.1-1
Chapter 1.1.1 --- Structure and properties of perovskite manganites --- p.1-1
Chapter 1.1.2 --- Structure and properties of niobium doped strontium titanate --- p.1-4
Chapter 1.1.3 --- Phase transition in perovskite manganites --- p.1-9
Chapter 1.1.4 --- Charge ordering and small polaron theory in PCMO --- p.1-15
Chapter 1.1.5 --- Colossal Magnetoresistance (CMR) in perovskite manganites --- p.1-19
Chapter 1.16 --- Review of semiconducting junction between perovskite manganites and niobium doped strontium titanate --- p.1-23
Chapter 1.2 --- Research motivation --- p.1-28
Chapter 1.3 --- Scope of this thesis --- p.1-29
References --- p.1-31
Chapter Chapter 2 --- Experimental details
Chapter 2.1 --- Thin film deposition --- p.2-1
Chapter 2.1.1 --- Facing-target sputtering --- p.2-1
Chapter 2.1.2 --- Vacuum system --- p.2-3
Chapter 2.1.3 --- Fabrication and characterization of manganites targets --- p.2-4
Chapter 2.1.4 --- Substrate --- p.2-7
Chapter 2.1.5 --- Deposition procedure --- p.2-8
Chapter 2.1.6 --- Silver electrode coating apparatus --- p.2-10
Chapter 2.2 --- Annealing systems --- p.2-12
Chapter 2.2.1 --- Vacuum annealing system --- p.2-12
Chapter 2.2.2 --- Oxygen annealing system --- p.2-14
Chapter 2.3 --- Characterization --- p.2-16
Chapter 2.3.1 --- Profilometer --- p.2-16
Chapter 2.3.2 --- X-ray diffractometer --- p.2-16
Chapter 2.3.3 --- Resistance measurement system --- p.2-18
Chapter 2.3.4 --- Current-voltage characteristics measurement system --- p.2-20
References --- p.2-23
Chapter Chapter 3 --- Epitaxial LCMO/STON heterojunction
Chapter 3.1 --- Four point and two point I-V measurement --- p.3-1
Chapter 3.2 --- Magnetic phase transition of LCMO revealed by four point I-V measurement of LCMO/STON heteroj unction --- p.3-8
Chapter 3.3 --- Oxygen annealing effect on LCMO/STON heteroj unction --- p.3-14
Chapter 3.4 --- Positive colossal Magnetoresistance in LCMO/STON heteroj unction --- p.3-16
References --- p.3-23
Chapter Chapter 4 --- Epitaxial PCMO/STON heterojunction
Chapter 4.1 --- Ohmic contact for PCMO thin films --- p.4-1
Chapter 4.2 --- PCMO charge ordering and magnetic phase transition --- p.4-9
Chapter 4.3 --- Four point I-V measurement of PCMO/STON heterojunction --- p.4-14
References --- p.4-16
Chapter Chapter 5 --- Epitaxial LCMO/PCMO/STON junction
Chapter 5.1 --- Tunneling junction fabrication --- p.5-1
Chapter 5.2 --- Structural characterizations --- p.5-2
Chapter 5.3 --- PCMO magnetic phase transition revealed by I-V measurement of LCMO/PCMO/STON tunneling junction --- p.5-3
Chapter 5.4 --- Energy band structure of perovskite manganites --- p.5-11
Chapter 5.4.1 --- Introduction to energy band of perovskite manganites and STON --- p.5-11
Chapter 5.4.2 --- Temperature dependent band structure of LCMO explained by diffusion voltage of LCMO/STON heterojunction --- p.5-18
References --- p.5-22
Chapter Chapter 6 --- Conclusions
Chapter 6.1 --- Conclusion --- p.6-1
Chapter 6.2 --- Future outlook --- p.6-3

From the time of the unexpected discovery of the insulating nature of NiO by Verwey half a century ago, Oxide materials have continued to occupy the centre stage of condensed matter physics. The recent discovery of high temperature superconductivity in doped cuprates has given a new impetus to the study of the strongly correlated electron systems. Besides, the occurrence of Colossal Magneto-Resistance (CMR) in doped rare earth manganite has also created renewed interest in these rather old systems. Understanding of the rich and complex phase diagram of these materials and their sensitivity to small perturbations e.g. external magnetic field of a few Tesla, temperature, change in isotope etc. are of great theoretical interest and also these materials have many potential technological applications. A common feature of all these oxide materials is that the transition metal ions have partially filled d-shells. Unlike s and p-electrons which gives rise to hybridized Bloch states, the d-electrons retain their atomic nature in a solid. This gives rise to strong Coulomb interaction among d-electrons which may be comparable or more than its kinetic energy. The strong correlation effects are evident from the experimental fact that the undoped parent compounds are insulators rather than metals as suggested by band theory, which favours a metallic state for systems with one electron per unit cell since this gives rise to partially filled bands (and hence a metallic state). These insulators termed Mott insulators, arise solely due to strong electron-electron correlations as compared to the band insulators which arise due to complete filling of one electron bands thereby giving rise to a gap (band gap)in the excitation spectra. The delicate competition between the kinetic energy and the Coulomb energy for d-electrons is broadly responsible for the wide variety of phenomena like Mott metal-insulator transition (MIT), magnetic transitions, charge ordering, orbital ordering, ferro/antiferroelectricity, and most interestingly the observation of high Tc superconductivity in doped cuprates. In this thesis we will restrict our interest to one such class of oxide materials, namely the doped rare earth manganites. In Chapter 1 we give a brief overview of the structure and basic interactions present in the doped manganites. Also, in the same Chapter we give a brief introduction to the phenomenology of manganites, particularly its phase diagram in the doping and temperature plane and various experimental features, e.g. the wide variety of phase transitions and phenomena particularly the observation of CMR, charge ordering and incipient meso-scale phase separations etc.. Then we briefly introduce a recently proposed microscopic model which is believed to be a minimal model which, for the first time, includes the three most important interactions present in the manganites namely the following -1)coupling of the orbitally degenerate eg electrons to local lattice distortions of Jahn-Teller type which gives rise to two species of electrons. The one denoted by by ℓ is associated with Jahn-Teller effects and hence is localized whereas the other denoted by b is an extended state and propagates through the lattice. 2) The strong Hund’s couplingof ℓ and b electrons to the t2g core spin and 3) the strong Coulomb correlation between the two species of electrons. Additionally, the model includes a new doping dependent ferromagnetic exchange between the t2g core spins which can arise from “virtual double exchange” mechanism which will be discussed in great detail in Chapter 1 . Finally, we give a brief account on Dynamical Mean Field Theory (DMFT) and Numerical Renormalization Group (NRG) as an impurity solver for the single impurity problem arising under single site DMFT approximation. In Chapter 2 we study the effect of inter-site ℓ - b hybridization on the ‘ℓ - b’ model. The single impurity problem arising under DMFT approximation has close connection with the Vigman-Finkelshtein (VF)model. Then we briefly introduce the VF model and bring out its close connection with the impurity problem. We consider both the particle-hole symmetric as well as the U → ∞ particle-hole asymmetric cases. We derive various spectral functions at T = 0K and discuss the nature of fixed points under various circumstances. We explicitly show that for the particle-hole symmetric case the Hamiltonian flows from X-ray edge singularity fixed point to Free Electron fixed point under Renormalization Group transformation. This is evident from the spectral properties of the model. We write down the effective Hamiltonian at the free electron fixed point. For the particle-hole asymmetric case the model flows from X-ray edge singularity fixed point to Free Electron/Strong Coupling fixed point with additional potential scattering terms. We write down the effective Hamiltonian at this fixed point and derive various leading order deviations. We found all of them to be irrelevant in nature also most interestingly the quasi-particles describing the under lying Fermi liquid state are found to be asymptotically non-interacting. We also calculate the Fermi liquid parameter, z, by analyzing the energy level structure of a non-interacting Hamiltonian with effective renormalized parameter. Also, we consider the case of ‘self consistent bath hybridization’ without ℓ - b hybridization for Bethe lattice with infinite coordination. Low energy qualitative features are found to be same but some of the high energy features get qualitatively modified. In Chapter 3 we discuss the transport properties of doped manganites in the insulating phases and also the Hall effect in the metallic phase. In the first part of this chapter we calculate the resistivity based on the ‘ℓ - b’model and try to fit it to the semiconducting form: ρ(T )= ρ0(T /T0)−nexp[Δ(T )/kBT ] and extract the “transport gap”, Δ(T ). This gap can be characterized in terms of the “spectral gap” which can be defined for the ℓ - b model. It is found that the transport gap in the paramagnetic phase can be characterized in terms of the near constant “spectral gap” in this phase whereas the same in the ferromagnetic phase can be characterized in terms of the zero temperature spectral gap. In the last part of this chapter we calculate the Hall resistivity (ρxy) of these materials in the metallic phase. Ρxy is found to be negative and linear in applied field -quite consistent with the experimental findings but this fails to explain the positive linear Hall resistivity at low temperatures and its crossover as a function of field and temperature. We then present a reasonable explanation for this discrepancy and support it by calculating the Hall density of states for a two band “toy model” involving inter species hybridization. In Chapter 4 we calculate the optical conductivity, σ(ω), in ℓ - b model. σ(ω) arises from two independent processes. One of the processes involves ‘b’ electrons only and termed as ‘b - b channel’ and this gives rise to a Drude peak in the low frequency region. another process termed as the ‘ℓ - b channel’ involves hopping of an ℓ-electron to a neighbouring empty site and transforms into a ‘b’like state. This process gives rise to a broad mid-infrared peak. The total conductivity is the sum of contributions from these two incoherent channels. Calculated σ(ω) for metallic systems shows lot of similarities with experimental observations particularly the temperature evolution of the mid-infrared peak and the spectral weight transfer between the two peaks. But for the insulating systems the calculated optical conductivity showed trends similar to more recent experimental observations on some insulating systems (x =0.125) but contradicts with earlier experimental observations on some other insulating system (x =0.1). Finally, in the concluding chapter, we summarize results from all the chapters and also sketch some possible future directions of investigations.

Wai, Kwai Fong = 錳氧化物 - 鈮摻雜之鈦酸鍶異構結的電流電壓關係測量 / 韋桂芳.
"Sept 2007."
Thesis (M.Phil.)--Chinese University of Hong Kong, 2007.
Includes bibliographical references.
Text in English; abstracts in English and Chinese.
Wai, Kwai Fong = Meng yang hua wu - ni shan za zhi tai suan si yi gou jie de dian liu dian ya guan xi ce liang / Wei Guifang.
Acknowledgement
Abstract
論文摘要
Table of content
List of Figures
List of Tables
Appendix A
Chapter Chapter 1 --- Introduction
Chapter 1.1 --- Structure and properties of perovskite manganites
Chapter 1.2 --- Magnetoresistance (MR)
Chapter 1.3 --- Giant Magnetoresistance (GMR)
Chapter 1.4 --- Colossal Magnetoresistance (CMR)
Chapter 1.4.1 --- Exchange interaction and CMR
Chapter 1.5 --- p-n junction
Chapter 1.5.1 --- Fundamentals of a p-n homojunction
Chapter 1.5.2 --- Deviations from the Ideal Diode
Chapter 1.5.2.1 --- Zener breakdown
Chapter 1.5.2.2 --- Avalanche
Chapter 1.5.3 --- Heterojunction
Chapter 1.6 --- Research motivation
Chapter 1.7 --- Scope of the thesis
References
Chapter Chapter 2 --- Experimental details
Chapter 2.1 --- Thin film deposition
Chapter 2.1.1 --- Facing target sputtering
Chapter 2.1.2 --- Vacuum system
Chapter 2.1.3 --- Deposition procedure
Chapter 2.2 --- Oxygen annealing system
Chapter 2.3 --- Silver electrode coating apparatus
Chapter 2.4 --- Characterization
Chapter 2.4.1 --- Alpha-step profilometer
Chapter 2.4.2 --- X-ray diffractometer
Chapter 2.4.3 --- Electrical transport property measurement
Chapter 2.4.3.1 --- Measurement of resistance as a function of temperature (RT)
Chapter 2.4.3.2 --- Measurement of I-V characteristics of a junction
References
Chapter Chapter 3 --- Epitaxial LSMO/STON heterojunction
Chapter 3.1 --- Sample preparation
Chapter 3.2 --- Results and Analysis
Chapter 3.2.1 --- Structural analysis
Chapter 3.2.2 --- R-T measurement
Chapter 3.2.3 --- I-V measurement
Chapter 3.2.3.1 --- Analysis of diffusion voltage and breakdown voltage
Chapter 3.2.3.2 --- Construction of energy band diagram of LSMO/STON at room temperature
Chapter 3.2.3.3 --- Investigating how the energy band structure varies with the temperature
Chapter 3.2.3.4 --- Further development of the energy band analyzing method to wide-p/narrow-n heteroj unction
Chapter 3.2.3.5 --- Forward-biased deviations from ideal
Chapter 3.2.3.6 --- Discussion on the reasons for deviations from ideal
Chapter 3.2.4 --- MR determination
References
Chapter Chapter 4 --- Epitaxial [LSMO/PCMO] multilayers and p-n junction
Chapter 4.1 --- [LSMO/PCMO]/NGO multi-layered thin films
Chapter 4.1.1 --- Sample preparation
Chapter 4.1.2 --- Results and analysis
Chapter 4.1.2.1 --- Structural analysis
Chapter 4.1.2.2 --- R-T measurement
Chapter 4.2 --- [LSMO/PCMO]/STON multi-layered junction
Chapter 4.2.1 --- Sample preparation
Chapter 4.2.2 --- Results and analysis
Chapter 4.2.2.1 --- Structural analysis
Chapter 4.2.2.2 --- R-T measurement
Chapter 4.2.2.3 --- I-V measurement
Chapter 4.2.2.3.1 --- Analysis of diffusion voltage and breakdown voltage
Chapter 4.2.2.3.2 --- Investigating the energy band structure as a function of temperature
Chapter 4.2.2.3.3 --- Forward-biased deviations from an ideal junction diode
Chapter 4.2.2.3.4 --- Review on MR calculation
Chapter 4.2.2.3.5 --- Analysis of MR of [LSMO(8 A ) /PCMO(8 A)]/STON and LSMO/STON
References
Chapter Chapter 5 --- [La0 4Ca0.6MnO3/La0.8Ca0.2MnO3］p-n junction
Chapter 5.1 --- Sample preparation
Chapter 5.2 --- Result and analysis
Chapter 5.2.1 --- Structural analysis
Chapter 5.2.2 --- R-T measurement
Chapter 5.2.3 --- I-V measurement
Chapter 5.2.3.1 --- Analysis of diffusion voltage and breakdown voltage
Chapter 5.2.3.2 --- Investigating the energy band structure as a function of temperature
Chapter 5.2.3.3 --- Forward-biased deviations from ideal
Chapter 5.2.3.4 --- MR analysis
Chapter Chapter 6 --- Conclusion
Chapter 6.1 --- Conclusion
Chapter 6.2 --- Future outlook

Colossal magnetoresistance (CMR), as the name implies, is the phenomenon of dramatic changes in resistance attendant upon application of a magnetic field. The typical CMR material is derived from perovskite manganites with the chemical formula Ln1−xAxMnO3, where Ln is the rare earth (Ln = La, Pr, Nd, Sm) and A is the divalent metal (A = Ca, Ba, Sr). The objective of this paper is to study the effects of the doping Nd and Pr at La site on La-Ba-Mn-O ceramics using solid state reaction. The characteristics and magnetotransport properties of CMR materials are investigated. Polycrystalline (La1−xPrx)0.67Ba0.33MnO3 (x = 0, 1/6, 1/3, 1/2, 2/3, 5/6, 1) and (La1−xPrx)0.67Ba0.33MnO3 (x = 0, 1/6, 1/3, 1/2, 2/3, 5/6, 1), are doped with Pr and Nd site based manganites, calcined at 900°C for 12 hours, pelletized and sintered at 1300°C for 24 hours have been synthesized and investigated. The magnetoresistance (MR) effects are measured using the four point probe technique. The magnetoresistance defined as MR% = (Ro−RH)/RH × 100 was measured at a magnetic field of H ≤ 1T at room temperature. The MR values were increased from 7.9–12.7% and from 7.9–12.3% for doping with Nd (x = 0.17) and Pr (x = 0.33) respectively. The electrical property, Tp was determined by using standard four-point probe resistivity measurement in a temperature range of 20 K to 300 K. The result shows that Pr and Nd dopants shift the value of TP to a lower temperature. In this paper the structural pattern and microstructure property of bulk samples have been investigated via XRD, AFM and SEM. XRD patterns show that these systems are in single-phase with orthorhombic distorted perovskite structures. The rms roughness for the AFM images has obtained for undoped and doped samples. SEM micrographs have shown that undoped samples are observed to be more compact than the doped samples doped due to the existence of pores. The potential of this research is to produce magnetoresistive read head such as read/write heads in computer disc-drives, position sensor, magnetoresistive random access memory (MRAM), biomagnetic sensor and magnetic accelerometers.