LaSrCoFeO6 is a rhombohedral perovskite, and can be reduced to the orthorhombic brownmillerite LaSrCoFeO5 in reducing atmospheres at around 600 deg C. This material is air sensitive and oxidises under ambient conditions to the rhombohedral perovskite LaSrCoFeO5.5. Whereas LaSrCoFeO6 is paramagnetic at 300 K, LaSrCoFeO5 and LaSrCoFeO5.5 are magnetically ordered at this temperature. In this experiment, we plan to use the in situ reaction cell to study the effect of oxygen content on the structure and magnetic properties of this system. Reduction of LaSrCoFeO6 to LaSrCoFeO5 will be achieved in situ, and this will be followed by the oxidation to LaSrCoFeO5.5 and finally back to LaSrCoFeO6. The structural and magnetic order will be monitored throughout to allow structure, composition and magnetic order to be correlated with temperature.