A high pressure-high temperature study of Bi2Sr2MnO6+δ(0.4 ≤ δ ≤ 0.7)

Polycrystalline Bi2Sr2MnO6+δ samples were subjected to a high pressure-high temperature process and the effects on crystal structure and magnetic properties recorded. The unit cell was found to expand anisotropically with the c axis length increasing at four times the rate of the a and b axes where (da/dP) = (db/dP) = 1.0 ± 0.2 × 10−3 åAMPa−1 and (dc/dP) = 3.5 ± 0. ÅMPa−1 with an overall unit cell volume expansion of 1%. The net oxidation state of the manganese decreased from +3 towards +2 with a resultant increase in TN. These changes can be attributed to the effect of removing interstitial oxygen from the structure which primarily changes the oxidation state of the manganese.