Co-Substitution Effect in Room-Temperature Ferromagnetic Oxide Sr(3.1)Y(0.9)Co(4)O(10.5)

We investigated the Co substitution effect for the magnetic properties in room-temperature ferromagnetic oxide Sr(3.1)Y(0.9)Co(4)O(10.5). The substituted element (Al and Ga) and low-spin state Co(3+), which was changed from a high-spin or intermediate-spin state by Al or Ga substitution, reduced the Curie temperature to even 1.5 times lower than the temperature estimated from a simple dilution effect. Al(3+) preferentially substituted for intermediate-spin-state Co(3+) in the ferrimagnetic CoO(6) layer and deteriorated the saturation magnetization of Sr(3.1)Y(0.9)Co(4)O(10.5). By contrast, Ga(3+) substituted for high-spin-state Co(3+) in the CoO(6) layer and/or the antiferromagnetic CoO(4.25) layer and enhanced the saturation magnetization per Co ion. These results indicate that the magnetic properties of Sr(3.1)Y(0.9)Co(4)O(10.5) can be controlled by selectively substituting for Co(3+) with different spin states.