Author(s): Ahn, KH; Wu, XW; Liu, K; Chien, CL | Abstract: The effect of Fe doping (l20%) on the Mn site in the ferromagnetic ((Formula presented)) and the antiferromagnetic ((Formula presented)) phases of (Formula presented) has been studied. The same ionic radii of (Formula presented) and (Formula presented) cause no structure change in either series, yet conduction and ferromagnetism have been consistently suppressed by Fe doping. Colossal magnetoresistance has been shifted to lower temperatures, and in some cases enhanced by Fe doping. Doping with Fe bypasses the usually dominant lattice effects, but depopulates the hopping electrons and thus weakens the double exchange. © 1996 The American Physical Society.

Magnetic properties and colossal magnetoresistance of LaÑCaÖMnO3 materials doped with Fe

The conductivity and magnetoresistance of La0.5Pb0.5Mn1−xCrxO3 (0.0⩽x⩽0.45) measured at 0.0 and 1.5 T magnetic field have been reported. All the oxide samples except x=0.45, showed metal insulator transition (MIT) between 158–276 K, depending on x. In contrast to the behavior of a similar sample La0.7Ca0.3Mn1−xCrxO3 showing no (MIT) for x⩾0.3, the Pb doped samples showed MIT even with x=0.35. The MIT peak temperature (Tp) shifts towards lower temperature with increasing x while magnetic field shifts Tp to the high temperature regime. The metallic (ferromagnetic) part of the temperature dependent resistivity (ρ) curve (below Tp) is well fitted with ρ(T)=ρ0+ρ2.5T2.5 indicating the importance of electron–magnon interaction (second term). We have successfully fitted the high temperature (T>θD/2, θD is Debye temperature) conductivity data, both in presence and in absence of magnetic field, with small polaron hopping conduction mechanism. Adiabatic small polaron hopping conduction mechanism is followed by the s...

Nature of small-polaron hopping conduction and the effect of Cr doping on the transport properties of rare-earth manganite La0.5Pb0.5Mn1−xCrxO3

Effect of Fe substitution on magnetocaloric effect in La0.7Sr0.3Mn1−xFexO3 (0.05≤x≤0.20)

The effect of particle size on the transport properties (resistivity and thermopower) of La0.5Pb0.5MnO3 has been investigated both in the presence and in the absence of magnetic field B=0.0–1.5 T (maximum). Grain size, dc conductivity; and the metal–insulator transition temperature Tp of the sample increase with increasing annealing time. Grain size has, however, comparatively little effect on the Seebeck coefficient S. Magnetoresistance is higher for the samples with smaller grain sizes. dc magnetic susceptibility also increases with increasing grain size. High temperature (T>θD/2) resistivity data well fit the small polaron hopping model. Polaron hopping energy WH decreases but polaron radius rp increases with the increase of grain size. In the metallic regime (for T<Tp), resistivity data fit well with ρ=ρ0+ρ2.5 T2.5 and the transport mechanism is attributed mainly to the magnon-carrier scattering (∼T2.5). In all the samples with different grain sizes, S changes sign below Tp. In contrast to magnetoresi...

Particle size and magnetic field dependent resistivity and thermoelectric power of La0.5Pb0.5MnO3 above and below metal–insulator transition

We have studied the effect of Fe substitution on magnetic and magnetocaloric properties in La0.7Sr0.3Mn1-xFexO3 (x = 0.05, 0.07, 0.10, 0.15, and 0.20) over a wide temperature range (T = 10-400 K). It is shown that substitution by Fe gradually decreases the ferromagnetic Curie temperature (Tc) and saturation magnetization up to x = 0.15 but a dramatic change occurs for x = 0.2. The x = 0.2 sample can be considered as a phase separated compound in which both short-range ordered ferromagnetic and antiferromagnetic phases coexist. The magnetic entropy change (DSm) was estimated from isothermal magnetization curves and it decreases with increase of Fe content from 4.4 J/KgK at 343 K (x = 0.05) to 1.3 J/KgK at 105 K (x = 0.2), under H = 5 T. The La0.7Sr0.3Mn0.93Fe0.07O3 sample shows negligible hysteresis loss, operating temperature over 60 K range around room temperature with refrigerant capacity of 225 J/Kg, and magnetic entropy of 4 J/kgK which will be an interesting compound for application in room temperature refrigeration.

Effect of Fe substitution on magnetocaloric effect in La0.7Sr0.3Mn1-xFexO3 (x = 0 to 0.2)

The effects of Fe doping on the magnetic, transport, and magnetoresistance properties are studied for La0.7Sr0.3Mn1−yFeyO3 (y=0–0.18) and La1−xSrxMn0.88Fe0.12O3 (x=0.1–0.50). For increasing y, a peak in the thermal dependence of the resistivity appears and develops at the temperature TPl lower than TC, while the another peak near TC becomes smaller and then disappears. At 78 K the La1−xSrxMn0.88Fe0.12O3 oxides are insulators for x 0.5 and only the lower-temperature metal–insulator transition peak appears for 0.25<x<0.45. With increase of x from 0.25, TPl increases, becomes maximum at x=0.4 and then decreases. The temperature dependence of resistivity for the doped samples is quite different from that of the undoped La1−xSrxMnO3 series.

Li Bao-he

Papers

Effect of Fe doping in La1−xSrxMnO3

Effect of Fe doping in La[sub 1−x]Sr[sub x]MnO[sub 3]