Ultrasonic velocity and elastic anomaly in charge-ordered Nd₀.₅Ca₀.₅Mn₁₋ₓCrₓO₃, Nd₀.₃La₀.₂Ca₀.₅₋ᵧSrᵧMnO₃ and Dy₀.₅₋zErzBa₀.₅CoO₃ magnetic ceramics / Suhadir Shamsuddin

Three series of charge-ordered compounds Nd0.5Ca0.5Mn1-xCrxO3 (NCMCO) (0≤x≤0.05), Nd₀.₃La₀.₂Ca₀.₅₋ᵧSrᵧMnO₃ (NLCSMO) (0≤y≤0.05) and Dy₀.₅₋zErzBa₀.₅CoO₃ (DEBCO) (0≤z≤0.05) ceramics were prepared using the solid-state reaction method. For NCMCO series, resistivity and susceptibility measurements for the x=0 sample showed an insulating behavior and an anti-ferromagnetic (AFM) transition at 230 K as well as a charge-ordering (CO) transition at 280 K. The substitution of Cr induces a ferromagnetic-paramagnetic (FM-PM) and metal-insulator (MI) transition as well as gradually suppressing the CO state due to weakening of the Jahn-Teller (JT) effect. Quenching to reduce the oxygen content of the x=0.05 sample caused the MI transition temperature to shift to lower temperatures most likely due to oxygen reduction. On the other hand, both longitudinal and shear velocities at 100 K increased significantly with Cr substitution indicating improvement in elastic properties. However, quenching of the x=0.05 sample slightly decreased both velocities and related elastic moduli

Observation of charge ordering signal in monovalent doped Nd0.75Na0.25-xKxMn1O3 (0 ≤ x ≤ 0.10) manganites

K doping in the compound of Nd0.75Na0.25-xKxMn1O3 (x = 0, 0.05 and 0.10) manganites have been investigated to study its effect on crystalline phase and surface morphology as well as electrical transport and magnetic properties. The structure properties of the Nd0.75Na0.25- xKxMnO3 manganite have been characterized using X-ray diffraction measurement and it proved that the crystalline phase of samples were essentially single phased and indexed as orthorhombic structure with space group of Pnma. The morphological study from scanning electron microscope showed there was an improvement on the grains boundaries and sizes as well as the compactness with K doping suggestively due to the difference of ionic radius. On the other hand, DC electrical resistivity measurement showed all samples exhibit insulating behavior. However, analysis of dlnρ/dT-1 vs. T revealed the clearly peaks could be observed at temperature 210K for x = 0 and the peaks were shifted to the lower temperature around 190 K and 165 K for x = 0.05 and x = 0.1 respectively, indicate the existence of charge ordering (CO) state in the compound. Meanwhile, the investigation on magnetic behavior showed all samples exhibit transition from paramagnetic phase to anti-ferromagnetic phase with decreasing temperature and the TN was observed to shift to lower temperature suggestively due to weakening of CO stat

Comparative study on structural, electrical transport and magnetic properties of cr-doped in charge-ordered Pr0.75Na0.25Mn1-Xcrxo3 and Nd0.75Na0.25Mn1-Ycryo3 manganites

Cr doping in charge-ordered Pr0.75Na0.25Mn1-xCrxO3 and Nd0.75Na0.25Mn1-yCryO3 have been synthesized using conventional solid-state method to investigate its effect on structural, electrical transport and magnetic properties. X-ray diffraction (XRD) analysis for both compounds showed that the samples were crystallized in an orthorhombic structure with Pnma group. The unit cell volume value decrease as the Cr-doped increased indicating the possibility of Mn3+ ion was replaced by Cr3+ due to the different of ionic radius. The temperature dependence of electrical resistivity showed an insulating behavior down to the lower temperature the both parent compound (x = 0 and y = 0). Successive substitution of Cr at Mn-site in Pr0.75Na0.25Mn1-xCrxO3 manganites induced the metal-insulator (MI) transition temperature around TMI~120 K and TMI~122 K for x = 0.02 and x = 0.04 samples respectively suggestively due to the enhancement of double-exchange (DE) mechanism as a result of suppress the CO state. Analysis of resistivity data of dlnρ/dT-1 vs. T in Nd0.75Na0.25Mn1-yCryO3 manganite, showed a peak around 210 K and 160 K for y = 0 and 0.02 samples respectively while no peak was observed for y = 0.05 sample indicate the charge-ordered (CO) weakened. AC susceptibility, χ ’ measurements in Pr0.75Na0.25Mn1-xCrxO3 exhibits paramagnetic to ferromagnetic-like with curie temperature, TC increases from 132 K for x = 0.02 to 141 K for x = 0.04 with Cr content indicate the suppression of CO state meanwhile in Nd0.75Na0.25Mn1-yCryO3 showed paramagnetic to anti-ferromagnetic transition as Neel temperature TN increases from 115 K for y = 0.02 to 125 K for y = 0.05

Effect of Ag-doped on electrical transport properties in Pr0.75Na0.25MnO3 manganites

The monovalent doped Pr0.75Na0.25-yAgyMnO3 (y = 0 – 0.10) manganites have been investigated by DC electrical resistivity to elucidate the influence of Ag-doped on the electrical transport properties. The electrical resistivity measurement shows that the y = 0 sample exhibits insulating behaviour from 300 K down to 50 K. A similar behaviour was also shown for y = 0.10 sample. However, a metal insulator transition temperature, TMI was observed at 110 K for y = 0.05 sample suggestively due to the revival of double-exchange (DE) mechanism as a result of weakening the Jahn-Teller effect in the compound. Apart from that, the resistivity behaviour at temperature region above the TMI for y = 0 – 0.10 samples were found to fit well with the variable range hopping model with the increasing of hopping and activation energy as the Ag concentration increased suggested due to the distortion of MnO6 octahedral. Whilst for the metallic region which is below the TMI, the resistivity data of y = 0.05 sample was fitted well with the combination of domain/grain boundary, electronelectron and electron-magnon scattering. As for that, the impact of Ag+ ions doped on Pr0.75Na0.25MnO3 shows the significant results on the electrical transport properties

Effect of Cr-doped on crystalline phase, surface morphology and electrical properties of charge-ordered Nd0.75Na0.25MnO3 ceramics

Nd0.75Na0.25Mn1-xCrxO3 (x = 0, 0.02 and 0.05) ceramics have been synthesized using solid-state reaction method and the crystalline phase, surface morphology as well as electrical properties were reported. Powder X-ray diffraction analysis revealed all samples showed single phase and crystallized in an orthorhombic perovskite-structure whose unit cell belongs to the space group of Pnma. The increment of Cr content influenced the lattice parameters and the calculated unit cell volume; this is suggested due to the difference of ionic radius between Mn3+ and Cr3+ ions. Scanning electron microscopy image for sample with x = 0 shown the grains was in irregular shape and inhomogeneous causing the grain boundaries was not clearly seen compared to the x = 0.02 and 0.05 samples. The temperature dependence of the electrical resistivity measurement for all samples showed insulating behavior down to lower temperature under zero magnetic field for all samples. However, analysis of resistivity data of dln/dT-1 vs T shows a peak around 210 K and 160 K for x = 0 and 0.02 samples respectively. No such peak has been observed for x = 0.05 sample. This may be an indication the charge-ordered (CO) state was weakened by Cr-doped

Crystalline phase, surface morphology and electrical properties of monovalent-doped Nd0.75Na0.25Mn1-yCoyO3 manganites

Perovskite-type manganites Nd0.75Na0.25Mn1-yCoyO3 (y = 0 – 0.05) have been investigated to clarify the influence of Co-doped on crystal phase and morphological study as well as electrical transport properties. The Nd0.75Na0.25Mn1-yCoyO3 samples are prepared via solid state synthesis method. X-ray diffraction analysis revealed all the samples are essentially single phased and the peaks are indexed to an orthorhombic structure with Pnma space. The morphological study from scanning electron microscope shows the improvement of the grains boundaries and sizes as well as the compaction of particles can be seen as cobalt doping increased. On the other hand, the temperature dependence of electrical resistivity measurements using four-point-probe technique indicates all samples maintained an insulator like behaviour down to low temperature. Analysis of the resistivity change with respect to temperature, dlnρ/dT-1 versus T reveals a slope changes of resistivity has been observed and a boarder peak exist for y = 0 sample and the peaks become significantly obvious for y = 0.02 and 0.05 samples. The peaks are observed in the range of charge ordering (CO) transition indicate the existence of CO in the system

Crystalline Phase, Surface Morphology and Electrical Properties of Monovalent-doped Nd0.75Na0.25Mn1-yCoyO3 Manganites

Perovskite-type manganites Nd0.75­Na­0.25­Mn­1-yCo­y­O­3­ (y = 0 – 0.05) have been investigated to clarify the influence of Co-doped on crystal phase and morphological study as well as electrical transport properties. The Nd­0.75­Na­0.25­Mn­1-yCo­y­O­3­ samples are prepared via solid state synthesis method. X-ray diffraction analysis revealed all the samples are essentially single phased and the peaks are indexed to an orthorhombic structure with Pnma space. The morphological study from scanning electron microscope shows the improvement of the grains boundaries and sizes as well as the compaction of particles can be seen as cobalt doping increased. On the other hand, the temperature dependence of electrical resistivity measurements using four-point-probe technique indicates all samples maintained an insulator like behaviour down to low temperature. Analysis of the resistivity change with respect to temperature, dlnÏ/dT-1 versus T reveals a slope changes of resistivity has been observed and a boarder peak exist for y = 0 sample and the peaks become significantly obvious for y = 0.02 and 0.05 samples. The peaks are observed in the range of charge ordering (CO) transition indicate the existence of CO in the system

Effect of Co3+ substitution on electro-magnetic properties of Pr0.75Na0.25mno3 and Nd0.75Na0.25mno3 manganites

This paper reports influences of cobalt (Co) substituted at Mn-site of Pr0.75Na0.25Mn1-xCoxO3 and Nd0.75Na0.25Mn1-yCoyO3 on structure, electrical transport and magnetic properties. All of the samples were prepared via standard solid state reaction method. X-ray diffraction measurement indicates that all samples were crystallized in an orthorhombic structure (space group Pnma). Resistivity measurement displays the x = 0 sample manifests an insulator behavior while metal-insulator transition was found at 108 K and 84 K for x = 0.02 and 0.05 respectively for Pr0.75Na0.25Mn1-xCoxO3. On the other hand, all of the samples for Nd0.75Na0.25Mn1-yCoyO3 showed insulator behavior down to low temperature and analysis of the resistivity change with respect to temperature, dlnρ/dT -1 versus T reveals a slope changes of resistivity have been recorded. Two obvious peaks were recorded from the analysis for y = 0.02 and 0.05 which can be suggested to the existence of charge order transition at the vicinity. For magnetic properties, x = 0 sample showed a paramagnetic-antiferromagnetic transition and further substitution of Co, x = 0.02 and 0.05, induce the paramagnetic-ferromagnetic transition and antiferromagnetic arrangement respectively. Meanwhile, further substitution of Co, y = 0.02 and 0.05 indicate antiferromagnetic transition with increasing TN as Co increased