Pramod Kumar; Rashmi Singh; L. D. Sanjeewa; Rachana Kumar
Abstract
In this paper, structural, magnetic and heat capacity of M2Fe2O(AsO4)2 compounds have been reported. Most interestingly, the magnetization at very low fields a complete negative magnetization was observed in both field cooling and zero field cooling in K2Fe2O(AsO4)2 and Rb2Fe2O(AsO4)2 compounds ...
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In this paper, structural, magnetic and heat capacity of M2Fe2O(AsO4)2 compounds have been reported. Most interestingly, the magnetization at very low fields a complete negative magnetization was observed in both field cooling and zero field cooling in K2Fe2O(AsO4)2 and Rb2Fe2O(AsO4)2 compounds whereas field cooled is positive in KCsFe2O(AsO4)2. A possible mechanism for the observed peculiar magnetic behavior is discussed, related to the competition of the single-ion magnetic anisotropy and the antisymmetric magnetization behavior in two crystallographically different FeO6 centers. We estimated the gap (D) opening at low temperature K2Fe2O (AsO4)2 KCs2Fe2O (AsO4)2 and Rb2Fe2O (AsO4)2, are 23.6 K, 23.9 K and 25 K respectively from heat capacity. Magnetic part of heat capacity at low temperatures follows the T 3 dependence, indicates that the low temperature magnetic state in all these compounds are antiferromagnetic.
Khalid Sultan; M. Ikram
Abstract
Results from a detailed investigation on the structural, optical, electrical and magnetic properties of polycrystalline bulk samples of La1-xCaxMnO3 (x=0, 0.3, 0.5 and 0.7) synthesized by solid state reaction method are presented. The Rietveld analysis of the X-Ray diffraction (XRD) profiles clearly ...
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Results from a detailed investigation on the structural, optical, electrical and magnetic properties of polycrystalline bulk samples of La1-xCaxMnO3 (x=0, 0.3, 0.5 and 0.7) synthesized by solid state reaction method are presented. The Rietveld analysis of the X-Ray diffraction (XRD) profiles clearly indicated that the XRD patterns are well fitted with orthorhombic structure. Raman spectral features revealed their finger print modes and irreducible representations at the brillouin zone center as per the group theory. It is also observed that as doping is increased, these compounds tend towards a cubic form. Ooptical band gap ‘Eg’ study reveals that the Eg decreases with Ca doping resulting in increase in conductivity. This is consistent with the resistivity measurements. In all the samples, except when x = 0.0 and 0.7, the resistivity at the highest temperature measured (ρ300 K) is less than that at 5 K (ρ5K), although for temperature T<Tp, the material shows a metal variation of ρ with temperature (d ρ/dT > 0) whereas the value of ρ300 K decreases as x increases. Magnetization study revealed that temperatures corresponding to magnetic transitions Tc increases with doping. It is observed that the composition x = 0.5 show both a paramagnetic to ferromagnetic transition and an antiferromagnetic transition. An effort has been made to relate above observed results in the compound with the structural changes brought about by Ca doping.Possible mechanisms such as activated transport and Zener double exchange are used to understand the phase diagram of these materials.
Usha Chandra; K. Asokan; V. Ganesan
Abstract
Nanocrystalline stoichiometric La0.8Sr0.2Mn0.8Fe0.2O3 manganites synthesized by sol gel technique were irradiated by 200 MeV Ag +16 ion beam at various fluences and investigated by X-ray diffraction (XRD), magnetization and high resolution Mössbauer spectroscopic techniques. The analysis of Mössbauer ...
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Nanocrystalline stoichiometric La0.8Sr0.2Mn0.8Fe0.2O3 manganites synthesized by sol gel technique were irradiated by 200 MeV Ag +16 ion beam at various fluences and investigated by X-ray diffraction (XRD), magnetization and high resolution Mössbauer spectroscopic techniques. The analysis of Mössbauer patterns were done using Kopcewicz et al. (2004) proposition considering Double exchange mechanism. Both XRD and Mössbauer spectroscopic analysis indicated isostructural vacancy formation at Mn site at the fluence 5x10 12 ions/cm 2 . The system showed amorphous phase at the higher fluence of 1x10 13 ions/cm 2 . The local electronic environments seen through high resolution Mössbauer spectroscopic technique on the irradiated systems were understood in terms of ferromagnetic coupling between different Mn environment surrounding Fe ions. This proposition is supported by enhanced magnetization observed in the irradiated samples (Kopcewicz et al., 2004). The similarity to the hydrostatic applied pressure (at low value) is seen through the transformation from Fe 4+ to Fe 3+ at low fluence.
V. K. Sharma; G.D. Varma
Abstract
Bulk samples of Zn1-xFexO (x=0.02 and 0.05) were synthesized via solid state reaction route by sintering in air at 800 o C. Some sintered samples were annealed in Ar/H2 at 800 o C for ~ 5 hrs. X-ray diffraction results reveal that the basic crystal structure of the as sintered and hydrogenated (Ar/H2) ...
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Bulk samples of Zn1-xFexO (x=0.02 and 0.05) were synthesized via solid state reaction route by sintering in air at 800 o C. Some sintered samples were annealed in Ar/H2 at 800 o C for ~ 5 hrs. X-ray diffraction results reveal that the basic crystal structure of the as sintered and hydrogenated (Ar/H2) samples corresponds to ZnO wurtzite structure together with some traces of ZnFe2O4 in the as sintered and Fe metal in the hydrogenated samples. The as sintered samples of both compositions show paramagnetic behaviour and after hydrogenation they exhibit ferromagnetic interactions at room temperature. Increase in the electrical conductivity has also been observed in the hydrogenated samples. The presence of small Fe clusters in the hydrogenated samples are expected to be responsible for the observed room temperature ferromagnetism.