We report on the observation of double transition - a first order and a second order transition in GdSiCoGe with x = 0, 0.1, 0.2 and 0.4 with the appearance of short-range ferromagnetic correlations. The first order phase transition is due to a combined magnetostructural transition from monoclinic paramagnetic phase to orthorhombic ferromagnetic phase on cooling while the second order transition arises from an orthorhombic paramagnetic to ferromagnetic phase on cooling. Structural studies show that the substituted compounds crystallize in a combination of GdSiGe and GdSi phases. Low-temperature X-ray diffraction measurements confirm the complete transformation from monoclinic to orthorhombic phase. DC magnetization measurements reveal an anomalous low field magnetic behaviour indicating a Griffiths-like phase. This unusual behaviour is attributed to the local disorder within the crystallographic structure indicating the presence of short-range magnetic correlations and ferromagnetic clustering, which is stabilized and enhanced by competing intra-layer and inter-layer magnetic interactions. The magnetostructural transition results in entropy changes (-ΔS) of 9 J kg K at 260 K for x = 0.1, 8.5 J kg K at 245 K for x = 0.2 and 4.2 J kg K at 210 K for x = 0.4 for a field change of 50 kOe. Co substitution induces compelling crystallographic and magnetoresponsive effects in the Gd-Si-Ge system, which could be useful for potential and smart applications such as solid-state magnetic refrigeration and sensitive magnetic switching from paramagnetic to ferromagnetic state. Universal curve analysis has been carried out on the substituted samples to study the order of the magnetic transition.
The effect of cobalt doping on the structural, magnetic and magnetocaloric properties of electron-doped manganite La 0.7 Te 0.3 Mn 1Àx Co x O 3 (x ¼ 0, 0.1, 0.2, 0.25, 0.3 and 0.5) has been investigated. The parent compound La 0.7 Te 0.3 MnO 3 crystallizes in a rhombohedral structure with R 3c space group. With the increase in Co concentration to x ¼ 0.2, a structural transition from rhombohedral (R 3c space group) to orthorhombic (Pbnm space group) is observed. X-ray photoelectron spectroscopy (XPS) indicates that the structural transition is due to the disordered distribution of Mn 2+ /Mn 3+ and Co 2+ /Co 3+ ions. All the samples undergo a paramagnetic-ferromagnetic (PM-FM) phase transition. With the increase in Co content to x ¼ 0.1, the unit cell volume increases with a decrease in both Mn-O-Mn bond angle and T c indicating a weakening of the double exchange interaction. However, with further increase in Co concentration, T c increases. The presence of competing ferromagnetic and antiferromagnetic interactions leads to a glassy behaviour at low temperatures for low Co doping concentrations. However, for higher Co concentrations, no such behaviour is observed. Arrott plots reveal a second order nature of magnetic transition for all the samples. The magnetic exchange interactions for x ¼ 0.3 and 0.5 follow the mean-field model. Magnetization results show that the magnetocaloric property of the electron-doped manganite is affected by the substitution of Co at Mn sites. Relatively large values of relative cooling power and broad temperature interval of the magnetocaloric effect make the present compounds promising for sub-room temperature magnetic refrigeration applications. www.rsc.org/advances 86144 | RSC Adv., 2015, 5, 86144-86155This journal is
In this study, the structural properties of La0.7Sr0.3MnO3 (LSMO) manganite synthesized in bulk and nano form have been analyzed in detail. The bulk LSMO was synthesized by the solid-state method whereas the LSMO nanoparticles was prepared using the sol-gel route. The structural properties of the prepared samples were examined using X-Ray diffraction (XRD). Rietveld refinement confirmed that all the samples crystallize in R-3c space group with a rhombohedral structure. Williamson-Hall (WH) Analysis using Uniform deformation model and Size strain plots (SSP) were employed to determine the average crystallite size and microstrain in the synthesized samples. SEM and TEM measurements have also been taken to analyse their size distribution.
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