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Structural and magnetic properties of La0.6Ca0.4−xSrxMnO3 manganites have been investigated for x = 0.0, 0.1 and 0.4. The Rietveld analysis of X-ray diffraction data indicates that, with increasing Sr content, a structural phase transition from rhombohedral to orthorhombic is occurred. Structural parameters are calculated and found to be dependent...
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... activation and the whole system becomes SPM. 53,54 The obtained value of T b (at 1 T) is about 19 and 31 K for the NPs and the NPs 400 C, respectively. It is found that post annealing at a medium temperature causes a slight increase in T b . ...
The emerging all-d-metal Ni(Co)MnTi-based Heusler compounds attract extensive attention because it can potentially be employed for solid-state refrigeration. However, in comparison to the abundant physical functionalities in bulk conditions, the hidden properties related to the NiCoMnTi-based Heusler nanoparticles (NPs) have not yet been investigated experimentally. Here, we present NiCoMnTi Heusler NPs that have been manufactured by spark ablation under Ar gas flow, and the related magnetic and microstructural properties have been studied. Compared with the bulk sample, it is found that the magneto-structurally coupled transition in the bulk sample has collapsed into a magnetic transition for the NPs sample. Superparamagnetic NPs with widely distributed dislocations have directly been observed by high-resolution transmission electron microscopy. For the NPs, the magnetocrystalline anisotropy constant is 3.54 × 104 J/m3, while the saturation magnetization after post-treatment has been estimated to be around 26 Am2 kg−1. Our current research reveals that Ni-Co-Mn-Ti-based quaternary NPs could show interesting properties for future nano-application, and the produced NPs will further expand the functionalities of this material family.
... A double exchange (DE) mechanism between pairs of Mn 3+ and Mn 4+ has been proposed to understand the interactions of charge and spin in manganites [9]. However, the CMR Goldschmidt's tolerance factor, tG, is an indicator of the formation of perovskite structures and researchers have been using it to verify the stability and distortion of manganite compounds [7,36,37]. The tolerance factor is defined as: + ...
... This increase can be linked to the larger ionic radius of La 3+ (1.30 Å) Goldschmidt's tolerance factor, t G , is an indicator of the formation of perovskite structures and researchers have been using it to verify the stability and distortion of manganite compounds [7,36,37]. The tolerance factor is defined as: The Rietveld refinement was carried out on the XRD patterns to determine the structural parameters. ...
... It can be observed that the increase in Mn-O bond length and the decrease in Mn-O-Mn bond angle weakened the DE coupling and hence reduced the T C [22]. The observed broader dχ'/dT peak minimum in NSSS is the result of the broad grain size distribution, as shown by the corresponding FESEM analysis [36]. In other words, the width of the FM-PM transition relies on the grain size distribution. ...
La0.7Sr0.3MnO3 (LSMO) and Nd0.7Sr0.3MnO3 (NSMO) possess excellent colossal magnetoresistance (CMR). However, research work on the neodymium-based system is limited to date. A comparative study between LSMO and NSMO prepared by sol–gel and solid-state reaction methods was undertaken to assess their structural, microstructural, magnetic, electrical, and magneto-transport properties. X-ray diffraction and structure refinement showed the formation of a single-phase composition. Sol–gel-synthesised NSMO was revealed to be a sample with single crystallite grains and exhibited intriguing magnetic and electrical transport behaviours. Magnetic characterisation highlighted that Curie temperature (TC) decreases with the grain size. Strong suppression of the metal–insulator transition temperature (TMI) was observed and attributed to the magnetically disordered grain surface and distortion of the MnO6 octahedra. The electrical resistivity in the metallic region was fitted with theoretical models, and the conduction mechanism could be explained by the grain/domain boundary, electron–electron, and electron–magnon scattering process. The increase in the scattering process was ascribed to the morphology changes. Enhancement of low-field magnetoresistance (LFMR) was observed in nano-grained samples. The obtained results show that the grain size and its distribution, as well as the crystallite formation, strongly affect the physical properties of hole-doped manganites.
This paper reports the addition of NiO nanoparticles into the LCMO nanocomposites through a simplified methodology in the heat treatment process compared to the previous work. Structural analysis showed that LCMO and NiO co-existed in the samples without the formation of other phases and confirmed their composite structures. The grain size distribution of samples was observed to become narrower and left-skewed as the concentration of NiO nanoparticles increased. This indicates that the NiO nanoparticles were distributed near the grain boundaries or on the grain surfaces. The presence of La, Ca, Mn, O, and Ni was confirmed by EDX analysis, and no additional impurities were noticeable, which revealed that the composites here are chemically pure in the composition. Temperature dependence magnetisation measurement (100–300 K) revealed the occurrence of ferromagnetic to paramagnetic transition. The Curie temperature, TC recorded at 260 K for all samples. However, the metal–insulator transition temperature, TMI was found to decrease from 246 to 120 K as the NiO content increased. Magnetoresistance of composites was observed to enhance over a wide temperature range at 10 kOe. The findings of LCMO: NiO composites in this work can set up a new perspective and unlock its potential to be utilised in magnetic field sensor element functioning at a wide range of temperatures.
Lanthanum-based LnBO3 perovskite oxides have demonstrated fascinating magnetic properties and spin-lattice coupling. In this work, we report an unusual thermal expansion anomaly coupled with the magnetic ordering in the cubic CeTiO3 with the vacancy of Ce ions. The magnetic behaviors and lattice thermal expansion at low temperature were systematically investigated using the temperature dependence of the magnetization measurements and low temperature X-ray powder diffraction. It is clearly revealed that there are two magnetic transitions in the cubic CeTiO3 from 5 to 350 K: one is a magnetic ordering-disordering transition at 300 K and the other one might be a change of the magnetic component near 32 K. Both the magnetization and hysteresis change correspondingly upon cooling. Intriguingly, a lattice thermal expansion anomaly is found below the magnetic ordering temperature, which indicates a strong coupling of spin and lattice, i.e., a magnetovolume effect (MVE). Our findings provide the possibility of adjusting thermal expansion behavior and magnetic properties by introducing a vacancy of Ln atoms in lanthanum-based perovskite oxides.
The structure, magnetic properties, and critical behavior of Nd0.6Sr0.2K0.2MnO3 compound are investigated. Rietveld refinement of the X-ray diffraction pattern shows that the examined sample is a pure single phase, crystallized in an orthorhombic Pnma structure. The nanometric size of crystallites calculated using Williamson-Hall method is validated by transmission electron microscopy micrographs. Magnetic measurements indicate a second-order ferromagnetic (FM)/paramagnetic (PM) transition at the Curie point Tc. Various techniques are used such as modified Arrott plot (MAP), Kouvel-Fisher method (KF), and critical isotherm analysis (CIA) to identify critical properties from isothermal magnetization data near critical regions. The deduced values are close to the 3D Ising model, proving the existence of a short-range ferromagnetic order in Nd0.6Sr0.2K0.2MnO3 sample. The results fully meet the requirements of the universal scaling assumption, further confirming its accuracy.
The Nd0.6Sr0.3K0.1MnO3 polycrystalline manganite is synthesized by using the sol–gel procedure. Structural, magnetic and magnetocaloric properties have been systematically investigated. The Rietveld refinement analysis indicates that studied compound is indexed in the orthorhombic system with Pnma space group. Magnetization data display a second-order magnetic phase transition from paramagnetic to ferromagnetic state at Curie temperature. The analysis of the magnetic entropy change is performed by using different methods: classical Maxwell equations and Landau mean-field model. Satisfactory accordance between both data is noticed. The maximum of the magnetic entropy change and the relative cooling power are found to reach 3.06 J.kg⁻¹.K⁻¹ and 180 J.kg⁻¹, respectively, under an external magnetic field of 5 T, making this material considered as potential candidate for room temperature magnetic refrigeration application. The critical exponents are deduced from the field dependence of the magnetic entropy change using a universal power law. The obtained values go in tandem with those related to the 3D-Ising model. According to the mean-field theory, the magnetic entropy change is invested to determine the spontaneous magnetization values. Results match reasonably well with those extracted from the classical extrapolation of Arrott plots.
We report the synthesis of Pr0.5Sr0.5MnO3 nanoparticles (NPs) by pulsed laser deposition (PLD) with varying energy per pulse (100, 200 and 300 mJ) under Ar (Argon) atmosphere. We have obtained NPs with average diameters of 10, 16, 19 nm, with narrow size distribution and core-shell morphology, in which the cores are crystalline and the shells amorphous. Due to the large amount of amorphous phase, heat treatment at temperatures of 750 and 900 °C was applied and X-ray diffraction with Rietveld refinement analyses indicated that highly crystalline PSMO NPs were obtained with an average diameter of 35 nm and 65 nm, respectively. Note that the annealing was also useful to tune the NPs size. Target magnetic investigation indicated that the Pr³⁺ and Mn³⁺/Mn⁴⁺ magnetic sublattices couple in an antiferromagnetic (AFM) fashion at low temperatures, undergoing a reversible transition to the ferromagnetic (FM) state around 200 K. However, heat-treated NPs behave differently – the ZFC and FC curves exhibit an irreversibility that is most likely associated with the weakening of AFM interactions on the surface of the NPs. Despite this characteristic, the NPs exhibit a sharp magnetic transition (FM-PM) with TC around 300 K, which makes these NPs useful candidates for magnetocaloric, magnetoresistivity and medicine applications.
A detailed study of structural, magnetic, magnetocaloric and magneto-transport properties of Nd0.6Sr0.4−xKxMnO3 (x = 0.0, 0.1 and 0.2) manganite, prepared using the sol–gel process, has been performed. All compounds are pure single phase crystallized in the orthorhombic system with Pnma space group. Rietveld analysis reveals the dependence of structural properties upon the monovalent substitution rate. The nanometric size determined through Debye–Scherrer formula is validated by SEM micrographs. Magnetization curves as a function of temperature exhibit a clear ferromagnetic to paramagnetic (FM-PM) phase transition at Curie temperature (Tc) which is found to decrease with increasing K fraction x. Large relative cooling power (RCP) value standing for about 50% of that noticed in pure Gd under magnetic field of 5 T is achieved for x = 0.0 compound, indicating its potential application in the cooling fields. Electrical resistivity curves as a function of temperature exhibit a metal–semiconductor (M-Sc) transition for all samples. The magnetoresistance (MR) ratio reaches its highest value for x = 0.2 sample under an external magnetic field of 2 T making this material a promising magnetoresistive sensor used in a wide range of industrial applications. Significant values of thermal coefficient of resistivity (TCR) are noted under zero external magnetic field giving these materials a potential application for the infrared (IR) and bolometric detectors.
Nd 0.6 Sr 0.4 MnO 3 polycrystalline manganite was synthesized by two different methods: the auto-combustion reaction (NSMO-AC) and the sol-gel method (NSMO-SG). The structural, magnetic, magnetocaloric and critical behavior of the samples were examined. Rietveld refinements of the XRD patterns revealed that both compounds are pure single phase indexed to the orthorhombic system adopting the Pnma space group. The nanometric size estimated using the Williamson-Hall method was confirmed by TEM micrographs. Magnetic measurements as a function of temperature indicated that both samples underwent a second order ferromagnetic (FM)-paramagnetic (PM) phase transition at Curie temperature (T C). The relative cooling power was observed to be around 95.271 J kg À1 for NSMO-AC and 202.054 J kg À1 for NSMO-SG at m 0 H ¼ 5 T, indicating that these materials are potential candidates for magnetic refrigeration application close to room temperature. The critical behavior was estimated using diverse techniques based on the isothermal magnetization data recorded around the critical temperature T C. The calculated values are fully satisfactory to the requirements of the scaling theory, implying their reliability. The estimated critical exponents matched well with the values anticipated for the mean-field model and the 3D Ising model for NSMO-AC and NSMO-SG, respectively, showing that the magnetic interactions depended on the process of elaboration.
