Magneto-transport characteristics of La1.4Ca1.6Mn2O7 thin film deposited by spray pyrolysis

Polycrystalline thin films of double layer manganite La_1.4Ca_1.6Mn_2O_7 (DLCMO) have been deposited by nebulized spray pyrolysis on single crystal LaAlO_3 substrates. These single phase films having grain size in the range 70-100 nm exhibit ferromagnetic transition at T_C ~ 107K. The short range ferromagnetic ordering due to in plane spin coherence is evidenced to occur at a higher temperature around 225 K. Insulator/semiconductor to metal transition occurs at a lower temperature T_P ~ 55K. The transport mechanism above T_C is of Mott`s variable range hopping type. Below T_C the current-voltage characteristics show non-linear behaviour that becomes stronger with decreasing temperature. At low temperatures below T_CA ~ 30K a magnetically frustrated spin canted state is observed. The DLCMO films exhibit resonable low field magnetoresistance and at 77K the magnetoresistance ratio is ~ 5% at 0.6 kOe and \~ 13% at 3 kOe.Comment: 14 pages, 7 figure

Effect of season, explants, growth regulators and sugar level on induction and long term maintenance of callus cultures of Ficus religiosa L.

The effects of antioxidant treatments, 2,4-D concentrations and sucrose level were examined in order to optimize the induction and long term maintenance of callus cultures of Ficus religiosa L. from different explants including nodal segments, inter-nodal segments and shoot apices. The explants subjected to incubation for 40 min in antioxidant solution (2% ascorbic acid + 2% citric acid) exhibited maximum percent culture establishment (73.33%). Establishment was reduced when incubation time was longer than 40 min. The explants collected in May and June gave maximum response (100 %). The highest frequency of callus induction (100%) was observed in nodal segments on Murashige and Skoog medium supplemented with 2.26 μM 2,4-dichlorophenoxyacetic acid and 3% sucrose after an average of 8.38 days. Maximum callus proliferation, resulting in fresh weight of 4.29 g after four weeks of culture, was also observed for callus initiated from nodal segments on the earlier mentioned medium. Higher concentrations of 2,4-D and lower concentrations of sucrose were found to be unfavourable for callus induction as well as proliferation. Callus cultures, initiated from nodal segments, could be  successfully maintained in healthy and proliferative form for consecutive nine months on the earlier said medium.Key words: Ficus religiosa L., explants, callus induction, callus proliferation,callus maintenance, in vitro

Comparative study of magnetic and magnetotransport properties of Sm0.55Sr0.45MnO3 thin films grown on different substrates

Highly oriented polycrystalline SSMO thin films deposited on single crystal substrates by ultrasonic nebulized spray pyrolysis have been studied. The film on LAO is under compressive strain while LSAT and STO are under tensile strain. The presence of a metamagnetic state akin to cluster glass formed due to coexisting FM and antiferromagnetic/charge order (AFM/CO) clusters. All the films show colossal magnetoresistance but its temperature and magnetic field dependence are drastically different. In the lower temperature region the magnetic field dependent isothermal resistivity also shows signature of metamagnetic transitions. The observed results have been explained in terms of the variation of the relative fractions of the coexisting FM and AFM/CO phases as a function of the substrate induced strain and oxygen vacancy induced quenched disorder.Comment: 21 page