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The modifications in electrical and magnetic properties of polycrystalline bulk La 0.7 Ca 0.3 Mn 1− x T x O 3 (T=Fe, Ga) samples at relatively higher doping concentration ( x =0.08–0.12) are investigated. All the synthesized, single phase samples were subjected to resistivity measurements in the temperature range 50–300 K. No insulator–metal transition ( T P ) was observed for Fe doped samples with x =0.12. For all the other samples the transition temperature decreased with increase in doping concentration. The small polaron hoping energy was found to increase, rather slowly, with increase in doping concentration. The effect on magnetic properties is also prominently observed with respect to doping element and doping concentration. Interestingly, with the increase in doping concentration, the Curie temperature ( T C ) and T P separate out significantly indicating decoupling of electric and magnetic properties. Changes in these properties have been analyzed on the basis of magnetic disorder introduced in the system due to the magnetic and nonmagnetic nature of these ions rather than strong lattice effects which is insignificant due to similar ionic radii of Fe +3 and Ga +3 when compared to that of Mn +3 .

Magnetic multilayers have attracted much attention due to their potential applications in spintronic devices because of their ability to inject spin-polarized current. The bilayer of ferrimagnetic Fe3O4 and manganites La0.7Ca0.3MnO3 (LCMO) is an interesting system due to the (i) fascinating electrical and magnetic properties of the spinel and perovskite material and (ii) high-spin polarization character of Fe3O4. In this work, we report our results on pulsed laser deposited thin films of Fe3O4/LCMO bilayer on LaAlO3 (LAO) substrate. For comparison, LCMO and Fe3O4 films were also grown on LAO substrate separately. The films were characterized by techniques such as X-ray diffraction, four-probe electrical resistivity with and without magnetic field. It is shown that oriented Fe3O4/LCMO bilayer can be grown successfully on the c-axis oriented LAO substrate. The electrical transport properties suggest that at low temperature the junction shows considerable magnetoresistance.

Polycrystalline bulk samples of La1–XBaXMnO3 (x = 0.5 – 0.65) were synthesized by solid state reaction route. Low temperature four probe resistivity measurements and a.c. susceptibility measurements were carried out on these samples after the analysis of powder XRD data with Rietveld fitting method. All the studied compounds showed paramagnetic to ferromagnetic transition at TC ∼ 330 K and also showed insulator-metal transition (at temperature TP) with no indication of charge-ordering. In La1−xBaxMnO3 case the insulator-metal transition is well below the magnetic transition. At x = 0.55, the difference in TP and TC is ∼ 90 K and also XRD pattern starts showing the existence of BaMnO3 phase which grows with x. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The effect of simultaneous substitution of a fluctuating cation and a divalent cation in LaMnO3 perovskite modifies the properties of the material to exhibit large valence colossal magnetoresistance (CMR) effect. A good example of these properties is (La1−2x Pr x Ca x )MnO3 (LPCMO) type CMR material. In this communication it is reported that, with the increase in x (for x=0.1, 0.15, 0.2), the T c varies between 100 and 120 K with improvisation in metal-insulator transition. Interestingly, resistance increases with x from few hundred ohms to few kilo ohms with corresponding decrease in the unit cell volume. The results of the studies using X-ray diffraction (XRD), electrical resistivity, magnetoresistance and ac susceptibility measurements on LPCMO samples for understanding the structural, transport and magnetic properties are discussed in detail.