Multiple Orbital Effects and Magnetic Ordering in a Neutral Radical

The
alternating ABABAB π-stacked architecture of the EtCN
solvate of the iodo-substituted, oxobenzene-bridged bisdithiazolyl
radical IBBO (space group Pnma) gives rise to strong
ferromagnetic exchange along the π-stacks, and the material
orders as a spin-canted antiferromagnet with TN = 35 K, with a spontaneous (canted) moment Mspont = 1.4 × 10–3 μB and a coercive field Hc = 1060
Oe (at 2 K). The observation of spin-canting can only be understood
in terms of multiorbital contributions to both isotropic and anisotropic
exchange interactions, the magnitude of which are enhanced by spin–orbit
effects arising from the heavy-atom iodine substituent. Pseudodipolar
interactions lead to a net canted moment along the c-axis, while the sublattice magnetization is predicted to possess
an easy a-axis.

碘代氧苯桥联双二噻唑基自由基IBBO的乙腈（EtCN）溶剂化物呈现交替ABABAB型π堆叠（π-stacked）结构，其空间群为Pnma。该结构沿π堆叠方向可产生强铁磁交换相互作用，令该材料成为自旋倾斜反铁磁体，奈尔温度（Néel temperature, TN）为35 K；在2 K条件下，其自发（倾斜）磁矩Mspont = 1.4×10–3 玻尔磁子（μB），矫顽场Hc = 1060奥斯特（Oe）。自旋倾斜现象仅能通过各向同性与各向异性交换相互作用的多轨道贡献加以解释，而重原子碘取代基引发的自旋轨道效应（spin–orbit effects）会增强这两类相互作用的强度。伪偶极相互作用（pseudodipolar interactions）会导致沿c轴的净倾斜磁矩，而亚晶格磁化（sublattice magnetization）的易轴（easy axis）为a轴。