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 Pr_0.6La_0.1Mg_0.3Mn_1?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 Pr_0.6La_0.1Mg_0.3MnO₃ 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 Pr_0.6La_0.1Mg_0.3MnO₃ compound is attractive as a possible refrigerant for low temperature magnetic refrigeration.     

Structural Magnetic and Electrical Properties in Nd-Doped Manganites (La0.70−x Nd x )Sr0.30Mn0.70Ti0.30O3 with 0 ≤ x ≤ 0.30

The structural, magnetic and electrical properties of (La_0.70?xNd_x)Sr_0.30Mn_0.70Ti_0.30 O ₃ perovskites (0 ≤ x ≤ 0.30) prepared by the usual ceramic procedure were investigated. Structural Rietveld refinements of the X-ray powder diffraction revealed that for x = 0 the compound crystallizes in a rhombohedral (R \(\bar {{3}}\) c) perovskite structure, while for x = 0.10, 0.20 and 0.30 the structure becomes orthorhombic (Pbnm). The field-cooled, zero-field-cooled and M(H) measurements lead to conclude that the samples with x≥0.10 behave like spin-glass systems. The temperature dependence of the resistivity exhibits two transitions at two temperatures T _p1 and T _p2, with the same width for the two peaks. T _P1 results from the competition between double-exchange and super-exchange mechanisms inside the grain (intrinsic effects) whereas T _P2 arises due to the grain boundary effects (extrinsic effect). The resistivity of this system seems to be related to the competition between antiferromagnetic insulating (AFI) phases, ferromagnetic insulating (FMI) phases and ferromagnetic metal (FMM) phases, which is induced by Nd doping effect.     

Structural and Electrical Properties of Monovalent Doped Manganites Pr0.6Sr0.4−x K x MnO3 (x=0, 0.05 and 0.1)

Structural and electrical properties of the mixed-valence monovalent doped manganites Pr_0.6Sr_0.4?x K _x MnO₃ (x=0, 0.05 and 0.1), prepared using the conventional solid-state synthesis method, have been investigated. Rietveld refinement of the X-ray diffraction patterns at room temperature shows a slight increase in unit cell volume with K content and confirms that all powder samples are single phase and crystallize in the orthorhombic structure with Pnma space group. Electrical resistivity measurements under and without magnetic field show a transition from the metallic to insulating behavior. The electrical conductivity is improved with increasing K content. The resistivity data in metallic region were fitted according to the electron–electron scattering process while in insulating region they were fitted using the small polaron hopping SPH model and Mott’s variable range hopping VRH model.     

Electrical Resistivity Behavior and VRH Transport Mechanism in Semiconducting La0.6Sr0.4Mn1−2x Fe x Cr x O3 (0.10≤x≤0.25) Manganites

The transport properties and conduction mechanism in La_0.6Sr_0.4Mn_1?2x Fe _x Cr _x O₃ (0≤x≤0.3) have been investigated. The undoped samples show metal–semiconductor transition with a peak of resistivity at a temperature T _P , whereas for all doped compounds the semiconducting behavior persists in the whole temperature range. The insertion of Cr³⁺ and Fe³⁺ ions leads to the increase of resistivity because the simultaneous substitution of Fe³⁺ and Cr³⁺ for Mn³⁺ reduces the number of available hopping sites for the Mn e _g↑ electron and suppresses the double-exchange mechanism. It was found that the transport mechanism for substituted samples is dominated by the variable range hopping of small polarons between localized states in a model where the various parameters estimated from Mott’s relation obey the variable range hopping (VRH) mechanism.     

Effect of Ni Doping on the Structural, Magnetic and Magnetocaloric Properties of Pr0.7Ca0.3Mn1−y Ni y O3 Manganites

In this paper, we report the structural, magnetic, and magnetocaloric properties of Ni-doped Pr_0.7Ca_0.3Mn_1?y Ni _y O₃ (0≤y≤0.1) powder samples. Our compounds were synthesized using the solid state reaction method at high temperature. X-ray diffraction analysis using Rietveld refinement show that all our samples are single phase and crystallize in the orthorhombic structure with the Pnma space group. Magnetization measurements versus temperature in a magnetic applied field of 50 mT reveal that Ni doping leads to a paramagnetic-ferromagnetic transition with a Curie temperature increasing from 106 K for y=0.02 to 118.5 K for y=0.1. A large magnetic entropy change |ΔS _M| has been observed in our doped samples with maximum values around their respective Curie temperatures T _C. $|\Delta S_{\mathrm{M}}^{\mathrm{max}}|$ is found to be 2 J?kg^?1?K^?1, 2.96 J?kg^?1?K^?1 and 2.94 J?kg^?1?K^?1 for y=0.02, 0.05, and 0.1, respectively, in a magnetic field change of 5 T. Large relative cooling power (RCP) value of 352.24 J?kg^?1 is obtained for Pr_0.7Ca_0.3Mn_0.9Ni_0.05O₃ sample under 5 T.     

The Structural and Magnetic Properties of Zn0.8−4x Dy x O y (0.05≤x≤0.10) Compounds Prepared by Solid-State Reactions

In this study, Dy-doped ZnO (Zn_0.8?4x Dy _x O _y (0.05≤x≤0.10)) samples were prepared by the solid-state reaction method, and were characterized by using the XRD, SEM and EDX techniques. The SEM results clearly demonstrate that the grains of the samples are very well connected to each other and tightly packed. From the XRD and EDX spectra, it has been concluded that the substituting of Dy³⁺ for Zn²⁺ in ZnO causes almost no change in the hexagonal wurtzite structure of ZnO. However, the lattice parameters a and c of Dy-doped ZnO are slightly different from those of the pure ZnO. These observations may be due to the slightly different ionic sizes of Zn²⁺ and Dy³⁺ ions. Our magnetization measurements (M–H) and (M–T) show paramagnetic behavior with a negative value of the Curie–Weiss temperature, corresponding to an antiferromagnetic exchange coupling in Dy-doped ZnO. Since, for low magnetic fields the extrapolation of the H/M versus temperature curves cut the T axes at negative values, we believe that the substitution of Dy in ZnO causes an overwhelming antiferromagnetic interaction for x≤0.10.     

Effects of Bismuth Doping on the Physical Properties of La0.6−x Bi x Sr0.4CoO3 (0≤x≤0.15) Cobaltites

The structural and magnetic properties of cobaltites with the nominal composition La_0.6?x Bi _x Sr_0.4CoO₃ (0≤x≤0.15) have been investigated. X-ray diffraction analysis using Rietveld refinement show that all our samples crystallize in the rhombohedral structure. The zero field cooled (ZFC) and field cooled (FC) magnetization curves at 50 mT exhibits thermomagnetic irreversibility signature of short range ferromagnetic interactions in our samples. The ferromagnetic–paramagnetic transition temperature decreases with increasing Bi amount. In the paramagnetic phase, all our synthesized samples obey to the Curie–Weiss law. The Curie–Weiss analysis suggests that the spin state of Co³⁺ is IS while Co⁴⁺ ions are in IS for x=0 and LS for x≥0.05. The Bi doping also leads to a weakening in the magnetic moment. The magnetic entropy change exhibits a maximum value which decreases from 2.28 J/kg?K for x=0 to 1.24 J/kg?K for x=0.15 upon a magnetic field change of 5 T.     

Magnetocaloric Effects in Pr0.6−x Er x Sr0.4MnO3 (0.0≤x≤0.2) Manganese Oxides

The effects of partial substitution of praseodymium by erbium on the structural, magnetic, and magnetocaloric properties of Pr_0.6?x Er _x Sr_0.4MnO₃ (0.0≤x≤0.2) powder samples have been studied. Our polycrystalline compounds were synthesized by the conventional solid state reaction at high temperature. Rietveld refinement of the X-ray diffraction patterns using Fullprof program shows that all our samples are single phase and crystallize in the orthorhombic structure with the Pnma space group. The unit cell volume decreased with increasing the Er amount. Magnetic measurements show that all our samples exhibit a paramagnetic–ferromagnetic transition with decreasing temperature. The Curie temperature T _C shifts to lower values with increasing Er content. From the magnetization isotherms at different temperatures, magnetic entropy changes ΔS _M and relative cooling power RCP have been evaluated. The maximum of the magnetic entropy changes for the Pr_0.45Er_0.15Sr_0.4MnO₃ sample is found to be $| \Delta S_{M}^{\max } | = 2.66~\mathrm{J}\,\mathrm{kg}^{-1}\,\mathrm{K}^{-1}$ under a magnetic applied field change of 2 T.     

Structural and Magnetic Properties of the Gd2−x Ho x Ru2O7 Pyrochlore Solid Solution (0≤x≤2)

In this paper, we investigate the structural and magnetic properties of the Gd_2?x Ho _x Ru₂O₇ (0≤x≤2) pyrochlores. X-ray diffractograms of all samples studied presented a cubic pyrochlore type crystal structure with lattice parameters varying linearly in accordance to Vegard’s law. It is shown that by substituting Gd by Ho one can tune the magnetic order of this system moving from antiferromagnetic (in the absence of Ho) to ferromagnetic (in the absence of Gd).     

Magnetic Properties and Metamagnetic Transition in SmCo1−x Fe x AsO (0≤x≤0.2)

Polycrystalline SmCo_1?x Fe _x AsO (x=0, 0.05, 0.1, 0.2) materials with single phase have been synthesized by solid-state reaction. According to the X-ray diffraction patterns, the a-lattice parameter shrinks, but the c-lattice parameter expends with the increased amount of Fe doping. Complicated magnetisms consist of antiferromagnetic, ferromagnetic, and paramagnetic have been observed between 5 K and 300 K in the present system. Magnetic measurement shows that with increasing Fe content, antiferromagnetic order of SmCoAsO is suppressed and ferromagnetic order is enhanced. Below their antiferromagnetic transition temperature, metamagnetic transition can be detected in samples with x<0.2, and the transition field decreases with increasing Fe content. When Fe content reaches 0.2, no metamagnetic transition is observed down to 5 K. A canting of the spins plays a crucial role in metamagnetic behavior of the present system.     

Structural, Raman Spectroscopy, and Magnetic Ordering in New Delafossite-Type Oxide CuCr1−x Ti x O2 (0≤x≤0.1)

We investigated in this paper a new mixture +3/+2 B cations delafossites by the doping at Cr³⁺ sites in CuCrO₂ by nonmagnetic cation Ti²⁺. Ceramics of CuCr_1?x Ti _x O₂ (0≤x≤0.1) were prepared via solid state synthesis techniques in a controlled atmosphere of O₂. The compound crystallized into the 3R delafossite phase with hexagonal structure. The slightly different size in B cations induced a slightly variation in unit cell parameters. We modulate the spin chirality by the effect of spin dilution for Ti²⁺ on the structural and magnetic properties of delafossite CuCrO₂ having a S=3/2 antiferromagnetic triangular lattice (ATL).     

Crystal Structures and Magnetic Properties of the Co2Mn1−x V x Sb (0 ≤ x ≤ 1) Heusler Compounds

Crystal structure and magnetic properties of the Co₂Mn_1?x V _x Sb (0 ≤ x ≤ 1) Heusler compounds have been studied by X-ray powder diffraction (XRD), magnetometric measurements, and full-potential linearized augmented plane wave (FP–LAPW) method. All compounds crystallize in a cubic Cu₂MnAl-type crystal structure with the space group Fm–3m. The samples for x<0.8 have the Curie temperatures above room temperature, while the Curie temperature is observed at 68 K for the sample with x = 0.8. The saturation magnetization at 5 K decreases linearly with increasing vanadium concentration x. The values of the saturation magnetization obtained by FP–LAPW–local density approximation (LDA) calculations are in better agreement with the experimental results compared with the results obtained by FP–LAPW–generalized gradient approximation (GGA) calculations.     

Fe substitution for Mn in Rhombohedral La0.8Sr0.2Mn1−xFexO3 — the Structural,Magnetic, and Magnetocaloric Properties

Journal of Superconductivity and Novel Magnetism - The effect of Fe doping on the structural, magnetic, and magnetocaloric properties was studied on La0.8Sr0.2Mn1?xFexO3...