Frustration effects in the spinel oxide Ge(Fe1−xCox)2O4

We studied magnetic properties of Ge-based spinel oxides Ge(Fe1−xCox)2O4 to verify the frustration effect. We discovered that the spin-glass-like behavior in Ge(Fe1−xCox)2O4 exists in 0 ≤ x ≤ 0.9, and coexists with the antiferromagnetic order in 0.1 ≤ x ≤ 0.9. Taking into account the coexistence of spin molecular excitations (frustration effect) and antiferromagnetic order in GeCo2O4 (x = 1), the spin-glass-like behavior coexisting with the antiferromagnetic order in Ge(Fe1−xCox)2O4 might be attributed to the freezing of the spin molecules by the substitution of Fe for Co.