PRESSURE-DEPENDENCE OF THE OXIDATION-STATE OF MANGANESE AND MAGNETIC PROPERTY OF CALAMGMNO6-X

Oxygen deficient perovskites CaLaMgMnO6-x were prepared in three diffe rent oxygen pressures; at 1150 degrees C under oxygen gas pressure of 0.1 MPa (L), at 950 degrees C under 0.1 GPa (M), and at 900 degrees C under high pressure of 6 GPa (H). From iodometric titration and EPR sp ectra, the samples could be formulated as (CaLa)((MgMnxMnyMn1-x-yIV)-M n-II-Mn-III)O-5.43 (2x-y=0.14) (L), (CaLaMgMn0.1Mn0.9O5.45)-Mn-III-O-I V (M) and (CaLaMgMn0.93Mn0.07O)-Mn-IV-O-VI5.57 (H), and it could be co nfirmed that MnBO (IV) ions are the most stable in an octahedral site of perovskites, but a small content of Mn(II), Mn(III) or Mn(VI) ions are also stabilized in an oxygen-vacant site due to the site preferenc es of such ions, depending on the oxygen pressure. The anomalous magne tic properties of L and M might result from the simultaneous occurrenc e of antiferromagnetism and ferromagnetism below T-C or T-N which coul d be explained by semicovalence magnetic exchange model.