Isostructural magnets (C1TET-TTF)FeX4 (X = Br, Cl) are featured with a triangle-based ladder lattice comprised of an Fe3+ zigzag chain where a donor dimer bridges between next nearest neighboring Fe3+ sites. The FeCl4- salt is an antiferromagnet with its easy axis tilted from the ladder sheet, the FeBr4- salt shows weak ferromagnetism, with the easy axis of its antiferromagnetic behavior lying on the sheet. We investigate the magnetic properties of mixed crystal (C1TET-TTF)(FeBr4)1 - x (FeCl4)x in order to reveal the origin of the differences in magnetism. The strengths of the exchange interactions varying with x can be understood on the basis of the inter-anion/donor atomic contact lengths in the crystal. Weak ferromagnetism survives with its easy axis tilted from the sheet in the concentration region x ≈ 0.2. Then weak ferromagnetism disappears above x ≥ 0.42. In the high concentration range x ∼ 0.4-0.8, the ordered state deviates from an ordinary antiferromagnet, due to the competition between two constituent exchange interactions. However, the possibility of a spiral spin which configuration theory predicts is not conclusive. The magnetic anisotropy, whose direction varies depending on x, is a consequence of the competition between the dipole-dipole interaction and the single-ion anisotropy.
等结构磁体 (C1TET-
TTF)FeX4 (X = Br, Cl) 具有基于三角形的梯形晶格,该晶格由 Fe3+ 之字链组成,其中一个供体二聚体桥接在下一个最近的相邻 Fe3+ 位点之间。FeCl4- 盐是一种反
铁磁体,其易轴与阶梯片倾斜;FeBr4- 盐显示出弱
铁磁性,其反
铁磁行为的易轴位于片上。我们研究了混合晶体 (C1TET-
TTF)(FeBr4)1 - x (FeCl4)x 的磁性,以揭示磁性差异的根源。交换相互作用的强度随 x 的变化而变化,这可以根据晶体中阴离子/阳离子间的原子接触长度来理解。在浓度 x ≈ 0.2 的区域,弱
铁磁性在其易轴与薄片倾斜的情况下仍然存在。然后,在 x ≥ 0.42 以上,弱
铁磁性消失。在 x ≥ 0.4-0.8 的高浓度范围内,有序态偏离了普通的反
铁磁体,这是由于两个组成交换相互作用之间的竞争造成的。然而,构型理论预测的螺旋自旋的可能性并不确定。磁各向异性的方向随 x 的变化而变化,这是偶极-偶极相互作用和单离子各向异性之间竞争的结果。