Site Preference and Possible Coexistence of Antiferromagnetic Order and Magnetic Frustration in (Co _{1– <i>x</i>} Mg _<i>x</i> ) ₁₀ Ge ₃ O ₁₆ (0 ≤ <i>x</i> ≤ 30%)

Geometrically frustrated magnetism has attracted tremendous attention, while chemical doping has been utilized as an important tool to probe frustrated magnetism in various systems. Here, we perform a systematic study by doping nonmagnetic Mg2+ into a magnetically complicated system, Co10Ge3O16, which contains three frustrated sublattices of Co2+, e.g., triangular Co1, Kagome Co2, and Co3 sublattices. By growing crystals for (Co1–xMgx)10Ge3O16 (0 < x ≤ 30%), we observed obvious site preference of Mg2+ on Co1 and Co3 sites over the Co2 site. Powder X-ray diffraction (XRD) patterns confirm the high purity of the samples and indicate a systematic peak shift, consistent with the loading compositions. Although previously investigated, the magnetic structure and expected magnetic frustration in this system have not been fully uncovered. Our temperature-dependent magnetic susceptibility measurements suggest that the high-temperature magnetostructural phase transition with antiferromagnetic ordering and a low-temperature broad peak are suppressed with Mg2+ doping, while two new magnetic features emerge at a high Mg2+ level. Moreover, the structural phase transition from the high-temperature R3̅m to the low-temperature C2/m space group is absent at the antiferromagnetic ordering temperature, as confirmed by single-crystal XRD. By analyzing the heat capacity and neutron powder diffraction results of the highest doped sample, (Co0.7Mg0.3)10Ge3O16, we speculate that the Co1 site is responsible for the long-range antiferromagnetic ordering, while the other two sites are short-range correlated in addition to a Mg2+-induced spin-glass state. This study provides more insights into the complex magnetism in Co10Ge3O16 by using the nonmagnetic Mg2+ as a probe. However, detailed magnetic structure requires further efforts for growing large single crystals.