Composite bulk polycrystalline samples of Agδ –La0.67Sr0.33–x –y Agx –δ Δy +δ MnO3 (x = 0.00, 0.15, 0.20, y = 0.00; and x = 0.15, y = 0.03, 0.05, with Δ representing cation vacancy at La site) were successfully synthesized using the sol–gel method. It is found that there are two phases in the samples, a cubic structure Ag phase and a perovskite phase. An experimental method for estimating the Ag phase content δ in the samples is presented. The Ag content x – δ and the cation vacancy y + δ were calculated. The Ag phase content and the lattice parameters of the two phases were also investigated using the Rietveld refinement method. The Ag phase contents obtained from the two methods are very close. The influences of x – δ and y + δ on the lattice parameters of the perovskite phase, the Curie temperature (T C), the metallic–semiconducting transition temperature (T MI), the magnetoresistance (MR), the peak temperature (T MR) of the MR, and the temperature stability of the MR of the samples were examined. The Mn–O bond length L B of the perovskite phase increases with increasing x – δ . However T C, T MI, and T MR decrease with increasing L B. For the sample Ag0.07–La0.67Sr0.13Ag0.08Δ0.12MnO3, under an applied magnetic field of 1.8 T, the MR is stable (9.41 ± 0.32%) in the temperature range 275–305 K; the MR increases linearly with magnetic field up to 1.5 T; and the change of MR with magnetic field, S MR = d(MR)/d(μ 0H ), is as high as about 5.2%/T. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The structural and magnetic properties of (Mn1−xFex)5Sn3 compounds have been investigated by x-ray diffraction and magnetic measurements. All the samples crystallize in the hexagonal Ni2In-type structure (P63/mmc) with the lattice parameters and cell volume decreasing almost linearly with the increase of Fe concentration. Besides the spin-glass state transition, the thermomagnetic curves show two other successive magnetic ordering transitions and their temperatures vary with x and show minima when x ∼ 0.2. With increasing Fe content, the difference between the two magnetic ordering temperatures becomes larger gradually from ∼12 K (x = 0) to ∼42 K (x = 0.5) and the magnetization at 5 K increases continuously. The −ΔSM(T) dependence for x = 0.45 exhibits two peaks, leading to a wide temperature range for magnetic refrigeration and thus a considerable magnetic refrigerant capacity (120 J/kg, ΔH = 5 T).
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