Polycrystalline Pr Research Articles

Structural, electrical and magnetic study of manganites Pr0.6Sr0.4MnO3 thin films

Thin polycrystalline Pr0.6Sr0.4MnO3 films were grown on the Y stabilized zirconium oxide substrates by magnetron sputtering using RF power and off-axis sputtering scheme with double cathodes. Only one polycrystalline phase with structural parameters consistent with that for the corresponding bulk sample was revealed in the films. Electric resistivity dependence on temperature demonstrates the shape characteristic for the substances with the Mott transition. The difference between magnetization temperature curves measured in the zero field cooling and field cooling modes was revealed. Magnetization field dependences were presented by the hysteresis loops changing their form with temperature.

Study of physical properties of cobalt substituted Pr0.7Ca0.3MnO3 ceramics

An investigation on single phase semiconducting polycrystalline Pr0.7Ca0.3MnO3 and Pr0.7Ca0.3MnCo0.1O3 crystallized in the orthorhombic system with Pnma space group is reported. We found that σDC increases when introducing Co for T<110K but for T>110K, it decreases. Also, the contribution of hopping process in conduction mechanism was in agreement with the Jonscher law and Mott theory. Capacitance was extensively dependent on temperature and frequency. A dielectric transition was observed at T=150K for the doped compound. The temperature dependence of dielectric permittivity is well described by Curie–Weiss law. The parameter of deviation from Curie–Weiss behavior to modified Curie–Weiss law is found to be ΔTm=30K. The substitution of Mn by Co was found to destroy the charge order state observed in the parent compound and to induce a ferromagnetic phase at low temperature. The cobalt-substituted sample exhibits a maximum value of magnetic entropy change |∆Smax|=3.2Jkg−1K−1and a large relative cooling power with a maximum value of 301J/kg under an applied field of 5T. Technically, these large values make the prepared material very promising for magnetic refrigeration.

Low temperature resistivity anomalies in Pr-based nano-manganites

The low-temperature electronic transport behavior of under doped polycrystalline Pr0.8Sr0.2MnO3 (PSMO) manganitenanoparticles (down to 40 nm), have been investigated in the presence of applied external magnetic fields (Hext) and adistinct resistivity minimum (ρmin) is observed below 50 K for each PSMO sample. It has been found that both depth of ρmin,and temperature of resistivity minima (min T ) values enhance with increase of Hext. Considering various possibilities likeCoulomb blockade theory, electron-electron interaction, phase separation, Kondo mechanism, we conclude thatoccurrence of low temperature resistivity anomalies (&lt;min T ) in PSMO manganite system is presumably due to acombined effect of electron-electron interaction (~T1/2) and 3D weak localization (WL) mechanism. The proposed modelcan explain spin dependent scattering phenomena in disorder background of correlated manganite system and behaviorof various fit parameters responsible for low temperature resistivity anomalies under external magnetic fields.

Structural, Magnetic, and Electrical Study of Polycrystalline Pr0.55Sr0.45−x Na x MnO3 (x = 0.05 and 0.1)

Structural, magnetic, magnetocaloric, and electrical properties of Pr0.55Sr0.45−x Na x MnO3 (x = 0.05 and 0.1) have been investigated. Our samples were elaborated using the conventional ceramic method at high temperature. Rietveld refinement of the X-ray diffraction patterns shows that all our compounds are single phase and crystallize in the orthorhombic structure with Pbnm space group. Low field magnetic measurements indicate that all investigated samples exhibit a paramagnetic–ferromagnetic transition with decreasing temperature. This transition takes place at room temperature. A large magnetocaloric effect has been observed in all our compounds. The maximum value of the magnetic entropy change is found to be 3.87 J K−1 kg−1 for the sample with x = 0.05 under 5T. The values of relative cooling power (RCP) are 246.52 J kg−1 for x = 0.05 and 262.73 J kg−1 for x = 0.1, respectively, for an applied magnetic field of 5T. The electrical resistivity measurements reveal a metal–semiconductor transition with increasing temperature with the presence of a resistivity minimum at low temperature which is attributed to the electron–electron columbic interactions.

Ferromagnetism, insulator-metal transition and magnetotransport in Pr0.58Ca0.42MnO3 films: role of microstructural perturbations

Magnetic and magnetotransport properties of oriented polycrystalline Pr0.58Ca0.42MnO3 thin films prepared in flowing oxygen (O2) and air ambient have been investigated. In the air, annealed film charge order (CO) is quenched and ferromagnetic (FM) transition, which appears at TC ≈ 148 K is followed by antiferromagnetic (AFM) transition at TN ≈ 104 K. This film shows self-field insulator-metal transition (IMT) at ≈ 89 K and ≈ 148 K in the cooling and warming cycle, respectively. Magnetic field (H) enhances and , reduces the thermo-resistive hysteresis. The film annealed in O2 shows a CO transition at TCO ≈ 236 K, which is followed by FM and AFM transitions at TC ≈ 158 K and TN ≈ 140 K, respectively. No self-field IMT is observed in this film up to H = 20 kOe. At H ≥ 30 kOe, IMT having sharp resistivity jumps appears at ≈ 66 K and ≈ 144 K in the cooling and warming cycle, respectively. As H increases the resistivity jumps disappear and ΔTIM decreases. In the lower temperature regime (T = 5 K and 40 K) the H dependent resistivity (ρ-H) measurements show that the frozen cluster state is more robust in the O2 annealed film. At temperatures around TC, the ρ-H hysteresis and H induced drop in resistivity are more prominent in the O2 annealed film. At TC < T < TCO, higher H is required to induce IMT in the O2 annealed film. The magnetic and magnetotransport data clearly show that the film annealed in O2 has higher fraction of the AFM/COI phase, while the air annealed film has higher fraction of FMM phase. The microstructural analysis of the two set of films employing high resolution transmission electron microscopy reveals that the air annealed film has higher density of microstructural disorder and lattice defects, which could be responsible for CO quenching, FM transition and self-field IMT.

Synthesis, magnetic properties and magnetostriction of Pr0.5Nd0.5([formula omitted]1.9 cubic Laves alloys

The structure, magnetic properties and magnetostriction of polycrystalline Pr0.5Nd0.5(Fe1-xCox)1.9 (0⩽x≤0.8) alloys were investigated. It is found that cubic Laves phase becomes the main phase only when the Co concentration is greater than 40 at.% under traditional vacuum annealed method. In contrast, the cubic Laves phase exists over the entire composition range studied in the samples annealed under high pressure. Both the lattice parameter and the Curie temperature decrease with the increasing Co concentration. The saturation magnetization increases into a maximum at x=0.1 and then decreases with further increase in x. The spin orientation phase diagram of Pr0.5Nd0.5(Fe1-xCox)1.9 (0⩽x≤0.4) alloys is constructed to illustrate the arrangement for the easy magnetization direction and crystal structure. The magnetostriction of Pr0.5Nd0.5(Fe1-xCox)1.9 alloys peaks at x=0.1. The Pr0.5Nd0.5(Fe0.9Co0.1)1.9 alloy combines a high magnetostriction with low cost advantage, which may make it potential material for magnetostrictive application.

Structural, magnetic and electrical study of polycrystalline Pr0.55Sr0.45−xKxMnO3 (x=0, 0.05 and 0.1)

We have investigated the effect of potassium doping on the crystallographic, magnetic, magnetocaloric and electrical properties of Pr0.55Sr0.45−xKxMnO3 with x=0, 0.05 and 0.1. Our samples have been elaborated using the solid state reaction at high temperature. Rietveld refinement of the X-ray diffraction patterns shows that all our samples are single phase and crystallize in the orthorhombic structure with Pbnm space group. Magnetization measurements versus temperature in a magnetic applied field of 0.05T show that all our samples exhibit a paramagnetic–ferromagnetic transition with decreasing temperature and that all the transitions are around room temperature. The value of the Curie temperature TC decreases with increasing potassium content. The maximum of the absolute value of magnetic entropy change in a magnetic applied field change of 5T increases from 3.33J/kgK for x=0 to 4.25J/kgK for x=0.1. The maximum value of relative cooling power recorded at 5T is about 247.51J/K for the sample with x=0.05. All the samples exhibit a metallic–semiconductor transition with increasing temperature.

High Pressure Effect on Superconductivity of Hole-Doped Pr0.75Sr0.25FeAsO Iron Pnictides

We report the pressure dependence of superconductivity for hole-doped polycrystalline Pr0.75Sr0.25FeAsO by the resistivity study using high pressure cubic and diamond anvil pressure cells. The superconducting transition temperature is initially increased from 17 K (P=0) to 34 K (P=6 GPa) with positive pressure coefficient, which is remarkable among other pnictide superconductors. At high pressure, there is no incredible enhancement of T c; in other words, it has a negative pressure effect on superconductivity, like in an electron-doped compounds. A systematic investigation of superconductivity for this 1111 type hole-doped iron pnictides is further carefully analyzed and discussed in detail using superconducting phase diagram under high pressure chart.

Effect of Fe Substitution on the Structural, Magnetic and Magnetocaloric Properties of Pr0.6La0.1Mg0.3Mn1−x Fe x O3 (0≤x≤0.3) Perovskite Manganites Prepared by Sol Gel Method

Studies of the structural, magnetic, and magnetocaloric properties of polycrystalline Pr0.6La0.1Mg0.3Mn1−x Fe x O3 (0≤x≤0.3) perovskite manganites were carried out. The compounds were synthesized using the sol–gel method. X-Ray diffraction (XRD) analysis using Rietveld refinement shows that all our compounds crystallize in the orthorhombic structure with the Pnma space group. The surface morphology and elemental analysis of both samples were carried out by scanning electron microscopy (SEM) and the energy dispersive X-ray technique (EDX), respectively. Magnetization measurements versus temperature under magnetic applied field of 0.05 T showed that all our investigated samples display a ferromagnetic-paramagnetic transition. The substitution of Mn by Fe leads to an increase of the Curie temperature T C from 64 K for x=0 to 380 K for x=0.3. The Arrott plots show that the phase transition is of second order. A large magnetic entropy change |ΔS M | deduced from isothermal magnetization curves has been recorded in the parent compound Pr0.6La0.1Mg0.3MnO3 reaching a maximum of 0.79 J/kg K under a magnetic applied field of 2 T close to T C . Our results on magnetocaloric properties suggest that the Pr0.6La0.1Mg0.3MnO3 compound is attractive as a possible refrigerant for low temperature magnetic refrigeration.

Low temperature ac electrical study of Pr0.5−xLaxCa0.5MnO3 (x = 0.0–0.4) ceramics by employing impedance spectroscopy

Polycrystalline Pr0.5−xLaxCa0.5MnO3 (x = 0.0–0.40) ceramics are synthesized by conventional solid state reaction method, and phase purity is confirmed by employing X-ray diffraction. Temperature dependent ac impedance spectroscopic measurements enable us to determine an increasing trend in resistance values of these samples with the decrease in temperatures. However, a decreasing trend in resistance values with increase in the La-doping at Pr-site is observed. A metal to insulator transition (MIT) is reported for x ≥ 0.2, which is shifted to higher temperature values with further increase of x doping. Two equivalent circuit models, i.e., (ReQe)(RgbQgb) and (ReQe)(RgbQgb)(RgQg) are employed to explain the impedance data with and without MIT, respectively. Mott variable range hopping model is found to be an appropriate model for defining the conduction mechanism of charge carriers in the semiconducting region. The decrease in the impedance with x doping is explained in terms of increase in the localization length obtained from the fitting of Rgb. Using tanδ results, thermally activated relaxation behavior is discussed for x = 0.0 and 0.1; whereas for x = 0.2, a temperature independent relaxation behavior is conferred due to the change in the hopping process of charge carriers.

Impact of sintering temperature on room temperature magneto-resistive and magneto-caloric properties of Pr2/3Sr1/3MnO3

Abstract Magneto-resistive and magneto-caloric properties of polycrystalline Pr 2/3 Sr 1/3 MnO 3 have been studied as a function of sintering temperature ( T s ) between 1260 and 1450 °C. Reitveld refinement of their X-ray diffraction ( XRD ) patterns confirms their single phase crystalline structure with orthorhombic Pbnm space group. The point of maximum value of temperature coefficient of resistance ( TCR max ) and Curie temperature ( T c ) decreased slightly with T s . Magneto-resistance ( MR ) and magnetic entropy ( ΔS M ) increased markedly with sintering temperature. This could be attributed to the observed sharpness of both the magnetic and resistive transitions due to better grain connectivity. Optimum results are obtained for the sample with T s = 1400 °C. MR at T c of the same is found to be as large as 32% at 1T and 58% at 5T magnetic fields. The maximum entropy change ( ΔS M max ) near its T c is 2.3 J kg −1 K −1 and 7.8 J kg −1 K −1 upon 1T and 5T fields change respectively. These characteristics [ MR (32% 1T, 58% 5T) and reasonable change in magnetic entropy (7.8 J kg −1 K −1 , 5T)] generate possibility that the optimized compound can be used as a potential magnetic refrigerant close to room temperature.

Change of conduction mechanism in the impedance of grain boundaries in Pr0.4Ca0.6MnO3

Freshly synthesized polycrystalline Pr0.4Ca0.6MnO3 sample has been analyzed by employing X-ray diffraction, magnetization and impedance spectroscopic techniques. Magnetization M(T) showed charge ordering (TCO) around 268K and below this temperature variation of magnetic and electric field effects is discussed. With the decrease of temperature, the change in the size and shape of the impedance plane plot is explored in terms of modulation of different relaxation processes. An equivalent circuit model (RQ) is used to determine the electrical parameters of Pr0.4Ca0.6MnO3 sample at different temperatures. Impedance of grain boundaries derived from the fitting of experimental data using an equivalent circuit model shows a change in conduction mechanism from small polaron hopping (SPH) to the variable range hopping (VRH) model around 148K. Activation energies calculated from the SPH model and relaxation frequencies of imaginary part of impedance are compared and discussed. Average normalized change (ANC) deduced from the impedance data illustrates a change in conduction mechanism around 148K due to the superexchange networks of Mn3+ and Mn4+.

Magnetocaloric effect and magnetothermopower in the room temperature ferromagnet Pr0.6Sr0.4MnO3

We have investigated magnetization (M), magnetocaloric effect (MCE), and magnetothermopower (MTEP) in polycrystalline Pr0.6Sr0.4MnO3, which shows a second-order paramagnetic to ferromagnetic transition near room temperature (TC = 305 K). However, field-cooled M(T) within the long range ferromagnetic state shows an abrupt decrease at TS = 86 K for μ0H &amp;lt; 3 T. The low temperature transition is first-order in nature as suggested by the hysteresis in M(T) and exothermic/endothermic peaks in differential thermal analysis for cooling and warming cycles. The anomaly at TS is attributed to a structural transition from orthorhombic to monoclinic phase. The magnetic entropy change (ΔSm = Sm(μ0 H)-Sm(0)) shows a negative peak at TC (normal MCE) and a positive spike (inverse MCE) at TS. ΔSm = −2.185 J/kg K (−3.416 J/kg K) with refrigeration capacity RC = 43.4 J/kg (103.324 J/kg) for field change of μ0ΔH = 1.5 T (3 T) at TC = 304 K is one of the largest values reported in manganites near room temperature. Thermopower (Q) is negative from 350 K to 20 K, which shows a rapid decrease at TC and a small cusp around TS in zero field. The MTEP [ΔQ/Q(0)] reaches a maximum value of 25% for μ0ΔH = 3 T around TC, which is much higher than 15% dc magnetoresistance for the same field change. A linear relation between MTEP and magnetoresistance and between ΔSm and ΔQ are found near TC. Further, ac magnetotransport in low dc magnetic fields (μ0 H ≤ 0.1 T), critical analysis of the paramagnetic to ferromagnetic transition, and scaling behavior of ΔSm versus a reduced temperature under different magnetic fields are also reported. Coexistence of large magnetic entropy change and magnetothermopower around room temperature makes this compound interesting for applications.

Dielectric relaxation with polaronic and variable range hopping mechanisms of grains and grain boundaries in Pr0.8Ca0.2MnO3

Polycrystalline Pr0.8Ca0.2MnO3 has been synthesized through solid state reaction route and phase purity is analyzed using synchrotron XRD. Magnetization M(T) showed Mn spin alignment due to ferromagnetic ordering around 125 K (TC), whereas M(H) showed an onset of non-linear behavior from 200 K and with temperature re-orientation of magnetic moment is discussed. The modulation of relaxation processes revealed different formations of impedance plane plots with temperatures. A change in equivalent circuit models from (R1C1)(R2Q2) to (R1C1)(R2Q2)(R3Q3) at 100 K is being reported. The analysis of the impedance data is carried out by calculating impedance of grains and grain boundaries. Fitted parameters derived from these equivalent circuit parameters showed a change in conduction mechanism from small polaronic hopping model (SPH) to Mott's variable range hopping (MVRH) model, around 125 K (TC). Carriers hop to larger distance with multiple activation energies and are described by MVRH below TC. Above this temperature, different trap centers start facilitating these carriers through SPH. Dielectric relaxation shows dispersion around 125 K and the origin of this polarization lies close to the relaxation derived from the grains and their interfaces.

Impedance Spectroscopy of Manganite Films Prepared by Metalorganic Chemical Vapor Deposition

Polycrystalline Pr(1-x)CaxMnO3 (PCMO) films were prepared by liquid source metalorganic chemical vapor deposition using in situ infrared spectroscopic monitoring. The electric properties of the PCMO-based devices with Ni and Al electrodes (Ni-PCMO-Ni and Al-PCMO-Al devices) were studied by dc current-voltage (I-V) measurements and ac impedance spectroscopy. The current varied linearly with the applied voltage in Ni-PCMO-Ni devices, while nonlinear behavior was observed in I-V curves for Al-PCMO-Al devices. Impedance spectra were also different between Ni-PCMO-Ni and Al-PCMO-Al devices. The Cole-Cole plots for the Ni-PCMO-Ni devices showed only a single semicircular arc, which was assigned to the PCMO bulk impedance. Impedance spectra for the Al-PCMO-Al devices had two distinct components, which could be attributed to the PCMO bulk and to the interface between the PCMO film and the Al electrode, respectively. The bias dependence of the impedance spectra suggested that the resistance switching in the Al-PCMO-Al devices was mainly due to the resistance change in the interface between the film and the electrode. The metal electrode plays an important role in the resistance switching in the PCMO-based devices. The choice of the optimum metal electrodes is essential to the ReRAM application of the manganite-based devices.

Magnetic and magnetocaloric properties of Pr 0.6− xEu xSr 0.4MnO 3 manganese oxides

Studies of the structural, magnetic and magnetocaloric properties of polycrystalline Pr 0.6− x Eu x Sr 0.4MnO 3 (0≤x≤0.15) perovskite manganites were carried out. Substitution for praseodymium with europium, with smaller ionic radius, induces local distortion in the 〈Mn–O–Mn〉 bonds and consequently causes a random distribution in the magnetic exchange interactions. The competition between magnetic interactions leads to the appearance of an inhomogeneous magnetic state in our samples. Pr 0.6− x Eu x Sr 0.4MnO 3 ( x = 0 , 0.05, 0.1 and 0.15) polycrystalline samples were prepared using the solid–solid reaction method at high temperature. The compounds yielded are single phase and crystallize in the orthorhombic system with the Pnma space group. The substitution of Eu for Pr leads to a decrease of the Curie temperature T C from 303 K for x = 0.00 to 260 K for x = 0.15 . All of our compounds exhibit a large magnetic entropy change with a maximum around 2.2 J/kg K under a magnetic applied field change of 2 T for all compounds.

Charge order quenching, Griffiths phase, and magnetotransport in polycrystalline Pr0.58Ca0.42−ySryMnO3 thin films

AbstractWe report the magneto‐electrical properties of polycrystalline Pr0.58Ca0.42−ySryMnO3 thin films as function of Sr doping (y). These films (thickness ∼300 nm) prepared by spray pyrolysis on LaAlO3 (100) single crystalline substrates are single phase and have orthorhombic structure. The Sr free films show charge ordering (CO) transition at TCO ≈ 240 K and the magnetic ground state has metamagnetic nature akin to the cluster glass (CG). Sr doping quenches CO and induces paramagnetic–ferromagnetic (PM–FM) transition with a systematic destabilization of the CG state. The PM–FM transition occurs at TC ≈ 182, 218, and 250 K for y = 0.06, 0.12, and 0.22, respectively. The Sr doping induced CO quenching also gives rise to the Griffiths phase (GP) at a temperature TG &gt; TC. The resistivity of the Sr free films shows insulating behavior typical to the CO state. An insulator–metal transition (IMT) is observed at TIM ≈ 198 K in the y = 0.06 film, which increases to 225 and 265 K at y = 0.12 and 0.22, respectively. At y = 0.12, the sharpest IMT that results in huge temperature coefficient of resistivity (TCR) ≈19%, suggests the occurrence of a bicritical state. The bicriticality is also supported by a huge low field magnetoresistance ≈40% at 3 kOe and colossal magnetoresistance ≈90% at moderate magnetic field of 10 kOe. The destabilization of the CO, the appearance of GP, and the bicritical state has been explained in terms of the phase fluctuations induced by Sr doping dependent quenched disorder.

Evidence of substrate induced charge order quenching, insulator metal transition, and colossal magnetoresistance in polycrystalline Pr0.58Ca0.42MnO3 thin films

We report the magnetoelectrical properties of polycrystalline Pr0.58Ca0.42MnO3 thin films (thickness∼300 nm) deposited on single crystal LaAlO3 (LAO) and SrTiO3 (STO) substrates. The films on LAO show charge ordering (CO) at TCO≈240 K, with a metamagnetic ground state akin to the cluster glass (CG). In PCMO/STO films the CO is quenched and enhanced magnetic moment in the CG state suggests stronger ferromagnetic component. The resistivity of the films on LAO and STO differ drastically, the former has temperature dependence typical to the CO state, while the later show thermal cycling dependent insulator-metal transition (IMT). The large hysteresis in the temperature dependent resistivity provides the evidence of cluster coexistence. The films on STO also exhibit colossal magnetoresistance (CMR∼91%) at moderate magnetic field (∼10 kOe). The CO quenching, IMT, and CMR are explained in terms of the substrate induced magnetoelectrical phase coexistence.

Unusually strong coherent response from grain-boundary Josephson network in polycrystalline Pr x Y1 − x Ba2Cu3O7 − δ

By applying a highly sensitive homemade AC susceptibility technique to Pr_{x}Y_{1-x}Ba_2Cu_3O_7 polycrystals (with x=0.0, 0.1 and 0.3), we observed very sharp Fraunhofer type low-field periodic oscillations of the real part of the AC susceptibility which were attributed to Josephson vortices penetrating intergranular regions of grain-boundary Josephson network in our samples. Assuming the Lorentz type distribution of single-junction contact areas, we were able to successfully fit the experimental data.

The effect of calcium and praseodymium deficiencies on the physical properties of Pr0.5Ca0.5MnO3

Structural and magnetic properties of small amount 5% of praseodymium and calcium deficiency of polycrystalline Pr0.5Ca0.5MnO3 manganite have been investigated. Our synthesized samples have been elaborated using the conventional solid state reaction at high temperature. Rietveld refinements of the X-ray diffraction patterns show that all our samples are single phase and crystallize in the orthorhombic structure with Pnma space group. Praseodymium deficiency leads to a decrease of the unit cell volume while calcium deficiency leads to an increase of the unit cell volume. Magnetization measurements show that the magnetic properties depend strongly on the nature of the deficiency.