Investigation of colossal magnetoresistance in bulk and thick film manganites

Abstract

The electrical transport, magnetoresistive and magnetic properties of polycrystalline bulk samples of Lai_xAxMn03 where A is Ca, Sr and 0 (vacancy) were studied for different values of x. The polycrystalline bulk samples were prepared by either solid state reaction or combustion techniques. Polycrystalline bulk samples of nominal chemical composition Lao 67Cao33Mn03 were prepared with a range of grain sizes (3 llm-20 llm). The influence of grain size and oxygen vacancies on magnetoresistance properties of these different grain size samples were studied. Oxygen vacancies were introduced by annealing in a reducing atmosphere. It was demonstrated that reoxygenation can be achieved by annealing at T-900°C in a flowing oxygen atmosphere. The relationship between resistivity and magnetisation was investigated at various temperatures. Thick films of Lao67Cao33MnO;, Lao63Y07Ca033Mn03 and Lao5sSro4SMn03 were fabricated on polycrystalline AhO), single crystal LaAI03 (100) and single crystal (00 I) yttria stabilised zirconia (YSZ) by a screen printing technique. Magnetoresistance as a function of field, temperature, and the effect of different annealing conditions on different substrates was investigated. An ac inductance rig was built to obtain a qualitative measure of ac susceptibility of manganite and superconductors