Spin reorientation and magnetic frustration in Fe_32+<i>δ</i>Ge_{35−<i>x</i>}Si_<i>x</i> with a kagome lattice broken by crystallographic intergrowth

Fe_32+<i>δ</i>Ge_35-<i>x</i>Si_<i>x</i> was synthesized using solid-state and chemical vapor transport reactions in both powder and single crystalline forms. Single crystal and high-resolution powder X-ray diffraction experiments revealed Fe_32+<i>δ</i>Ge_35-<i>x</i>Si_<i>x</i> to be the third member of the Fe_32+<i>δ</i>Ge_35-<i>x</i>E_<i>x</i> (E = p-element) family of ternary compounds alongside Fe_32+<i>δ</i>Ge₃₃As₂ and Fe_32+<i>δ</i>Ge_35-<i>x</i>P_<i>x</i>. Fe_32+<i>δ</i>Ge_35-<i>x</i>Si_<i>x</i> features a two-dimensional intergrowth structure of two parent structure types: MgFe₆Ge₆ and Co₂Al₅. Similar to the other members, the stabilisation of the intergrowth structure in Fe_32+<i>δ</i>Ge_35-<i>x</i>Si_<i>x</i> occurs as a result of p-element substitution in the MgFe₆Ge₆-type block. The intergrowth breaks the kagome net of MgFe₆Ge₆ into individual hexagrams while providing additional layers of geometrically frustrated atomic arrangements. Magnetic measurements showed antiferromagnetic ordering at <i>T</i>_N ∼ 150-160 K and spin reorientation below 80-90 K owing to the competition between magnetic interactions in the frustrated magnetic lattice of Fe_32+<i>δ</i>Ge_35-<i>x</i>Si_<i>x</i>.