This study presents the influence of polymorphism on the magnetic properties of Co₅TeO₈. This compound with a spinel-like structure [Co₂]^A[Co₃Te]^BO₈ was synthesized into two polymorphs: one disordered within a cubic Fd3̅m structure, where Co²⁺ and Te⁶⁺ ions are randomly distributed on the octahedral B sites [the disordered polymorph can also be presented as an inverse spinel of the formula Co(Co_1.5Te_0.5)O₄] and the other ordered with a cubic P4₃32 structure where Co²⁺ and Te⁶⁺ ions are ordered on the B sites. The macroscopic magnetic measurements showed that both polymorphs present a ferrimagnetic ordering, below ∼40 K, and a second transition is also observed at 27 K for the ordered polymorph. Neutron powder diffraction data between room temperature and 1.7 K showed as well the presence of short-range magnetic ordered clusters, which appears for both polymorphs below 200 K. At lower temperature, these short-range orders are transformed into long-range ferrimagnetic orders. Below T_C = 40 K, the colinear ferrimagnetic structure of the disordered polymorph is described with the I4₁/am′d′ space group. The ordered polymorph undergoes an incommensurate ferrimagnetic spiral spin ordering below T_C1 = 45 K, followed by a second magnetic phase transition at T_C2 = 27 K. This last transition is associated with the emergence of an additional ferrimagnetic component and an abrupt change in the magnitude of the magnetic propagation vector k = [0, 0, γ] from γ = 0.086 at T = 30 K to γ ≈ 0.14 in the range between 27 and 1.7 K. The magnetic symmetry of the ordered polymorph is described with the P4₃(00γ)0 magnetic superspace group. We evidenced that the ordering of Co²⁺/Te⁶⁺ on the B sites changes all of the Co–Co and Co–O distances and thus all J_AB, J_AA, and J_BB exchange interactions, between the A and B sites, which are able to stabilize the incommensurate spin modulation in the ordered polymorph.

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多晶型对Co5TeO8尖晶石磁性的影响

本研究介绍了多晶型对 Co ₅ TeO ₈磁性能的影响。这种具有尖晶石状结构 [Co ₂ ] ^A [Co ₃ Te] ^B O _{8 的}化合物被合成为两种多晶型物：一种在立方Fd 3̅ m结构内无序，其中 Co ²⁺和 Te ⁶⁺离子随机分布在八面体 B 位点 [无序多晶型也可以表示为式 Co(Co _1.5 Te _0.5 )O ₄的反尖晶石] 和另一个有序的具有立方P 4₃ 32 结构，其中 Co ²⁺和 Te ⁶⁺离子在 B 位点排列。宏观磁性测量表明，两种多晶型物都呈现亚铁磁有序，低于~40 K，并且在 27 K 处也观察到有序多晶型物的第二次转变。室温和 1.7 K 之间的中子粉末衍射数据也表明存在短程磁性有序簇，这对于低于 200 K 的两种多晶型物都会出现。在较低温度下，这些短程有序转变为长程亚铁磁序。在T _C = 40 K 以下，无序多晶型物的共线亚铁磁结构描述为I 4 ₁ / am 'd ′ 空间群。有序多晶型在T _C1 = 45 K以下经历不相称的亚铁磁螺旋自旋排序，然后在T _C2 = 27 K处发生第二次磁相变。最后一次相变与额外亚铁磁成分的出现和磁传播矢量的大小k = [0, 0, γ] 从T = 30 K 时的γ = 0.086到 27 到 1.7 K 范围内的 γ ≈ 0.14。有序多晶型物的磁对称性用P 4描述₃ (00γ)0 磁超空间群。我们证明了 Co ²⁺ /Te ⁶⁺的顺序B 位点上的所有 Co-Co 和 Co-O 距离都会改变，因此A 和 B 位点之间的所有J _AB、J _AA和J _BB交换相互作用都能够稳定有序的不相称的自旋调制多晶型。