Abstract
We investigated the Co substitution effect for the magnetic properties in room-temperature ferromagnetic oxide Sr3.1Y0.9Co4O10.5. The substituted element (Al and Ga) and low-spin state Co3+, 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. Al3+ preferentially substituted for intermediate-spin-state Co3+ in the ferrimagnetic CoO6 layer and deteriorated the saturation magnetization of Sr3.1Y0.9Co4O10.5. By contrast, Ga3+ substituted for high-spin-state Co3+ in the CoO6 layer and/or the antiferromagnetic CoO4.25 layer and enhanced the saturation magnetization per Co ion. These results indicate that the magnetic properties of Sr3.1Y0.9Co4O10.5 can be controlled by selectively substituting for Co3+ with different spin states.
Highlights
Among transition metal oxides with various functions, cobalt oxides are especially interesting compounds and attract attention from many researchers
The spin state of Co3+ ions is strongly related to the functions and phenomena of the cobalt oxides, and unraveling the origins of these functions has opened up new material design guidelines
The octahedral CoO6 layer and the oxygen-deficient CoO4.25 layer, which consists of tetrahedral CoO4 and pyramidal CoO5, are stacked alternately [16–19]
Summary
Among transition metal oxides with various functions, cobalt oxides are especially interesting compounds and attract attention from many researchers. The spin state of Co3+ ions is strongly related to the functions and phenomena of the cobalt oxides, and unraveling the origins of these functions has opened up new material design guidelines. The octahedral CoO6 layer and the oxygen-deficient (tetrahedral/pyramidal) CoO4.25 layer, which consists of tetrahedral CoO4 and pyramidal CoO5 , are stacked alternately [16–19]. In this system, the two structural-phase transitions have been revealed in Sr3.12 Er0.88 Co4 O10.5 [20,21]. Perovskite unit cell, changes into monoclinic A2/m with a 2 2a × 2 2a × 4a supercell due to oxygen vacancy ordering at 509 K. The lowest-temperature phase, in which the a-axis is doubled
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