A high-temperature, controlled atmosphere Faraday magnetometer has been used to measure the magnetic susceptibility of La 1-x Sr x CoO 3-δ (LSC) as a function of temperature, Sr content (x), and oxygen nonstoichiometry (δ). Above 800 °C the magnetic susceptibility becomes independent of Co oxidation state and Sr doping, consistent with metallic valance electrons. Under these conditions, conductivity measurements as a function of x, T, and δ exhibit classic metallic behavior, with resistivity scaling linearly with temperature and nonlinearly with defect concentration. However, a large Curie-Weiss susceptibility persists even at high temperatures, suggesting the coexistence of more localized electron configurations. We discuss this behavior in terms of existing theories of electronic and magnetic structure.

We report the design of a Faraday balance that can be used to measure the magnetization of transition metal oxides at high temperatures and under controlled atmosphere. The instrument is sufficiently sensitive and stable to quantify the magnetic force on diamagnetic and paramagnetic samples at temperatures up to 1000 degrees C and in oxygen partial pressures as low as 100 ppm. We demonstrate the performance of the instrument by presenting preliminary magnetic measurements of lanthanum strontium cobalt oxide (La1-xSr(x)CoO3-delta) and aluminum oxide (Al2O3).

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High temperature/controlled atmosphere magnetic measurements using a Faraday magnetometer were used to probe the electronic structure of La1- xSrxCoO3-δ (LSC). We find that high temperature magnetic behavior of La1- xSrxCoO3-δ as a function of oxygen nonstoichiometry suggests co-existence of localized and delocalized electronic states. Above 800{degree sign}C oxygen exchange with the gas principally involves delocalized electrons, while at lower temperatures the situation becomes more complex. We discuss this behavior in the context of existing theories of electronic structure, as well as electron transport properties.