[in Japanese]

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We investigated magnetic properties of spinel oxides Ge(Co_1-xMg_x)₂O₄ with x = 0 ～ 0.5 to study the spin-orbit dilution effects on the magnetism of spin-orbit frustrated spinel GeCo₂O₄. We discovered that the magnetic moment per single Co²⁺ ion is decreased with increasing nonmagnetic Mg²⁺ ion concentration, which indicates the spin-orbit decoupling caused by the spin-orbit dilution. Additionally, small-amount substitution of Mg²⁺ for Co²⁺ causes the rapid increase of the positive Weiss temperature indicating the enhancement of ferromagnetic interactions, while the Mg²⁺ substitution suppresses the antiferromagnetic ordering resulting in the appearance of spin glass behavior. The present results suggest that the spin-orbit dilution causes the spin-orbit decoupling and the reinforcement of ferromagnetic frustration in GeCo₂O₄.

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