Spin-Crossover in a New Iron(II)/Di(pyrazolyl)pyridine Complex with a Terpyridine Embrace Lattice. Thermally Induced Excited Spin State Trapping and Clarification of a Structure−Function Correlation

The complex salts [FeL2]X2 (1X2; L = 2,6-di{4-fluoropyrazol-1-yl}pyridine; X– = BF4– or ClO4–) exhibit abrupt spin-transitions with narrow thermal hysteresis, at T1/2 = 164 K (X– = BF4–) and 148 K (X– = ClO4–). The transition in 1[ClO4]2 is complicated by efficient thermally induced excited spin-state trapping (TIESST) of its high-spin state below ca. 120 K, and the fully low-spin state was achieved only inside the magnetometer at a scan rate of 0.5 K min–1. Crystals of 1[BF4]2 are tetragonal (P421c, Z = 2; phase 1) at 300 K but transform to a highly twinned monoclinic phase 2 (P21, Z = 2) at 285 ± 5 K. These are forms of the “terpyridine embrace” crystal lattice, which often affords cooperative spin-transitions in iron/di(pyrazolyl)pyridine complexes. Phase 2 of high-spin 1[BF4]2 shows a significant temperature dependence by powder diffraction, which reflects increased canting of the monoclinic unit cell as the temperature is lowered. In contrast, 1[ClO4]2 retains phase 2 between 100 and 300 K, and was crystallographically characterized in its thermally trapped metastable high-spin state at 100 K, as well as its thermodynamic high- and low-spin forms at higher temperatures. The spin-crossover transition temperature in 1[ClO4]2 and related compounds correlates well with a parameter describing angular changes to the metal coordination sphere during the transition but not with other commonly used structural indices. The TIESST metastable high-spin state of 1[ClO4]2 shows no single molecule magnet properties at 2 K

Surface states and Rashba-type spin polarization in antiferromagnetic MnBi2Te4 (0001)

The layered van der Waals antiferromagnet MnBi2Te4 has been predicted to combine the band ordering of archetypical topological insulators such as Bi2Te3 with the magnetism of Mn, making this material a viable candidate for the realization of various magnetic topological states. We have systematically investigated the surface electronic structure of MnBi2Te4(0001) single crystals by use of spin- and angle-resolved photoelectron spectroscopy experiments. In line with theoretical predictions, the results reveal a surface state in the bulk band gap and they provide evidence for the influence of exchange interaction and spin-orbit coupling on the surface electronic structure

The Multicultural First World War: memories of the West Indian contribution in contemporary Britain

The experiences of West Indian soldiers in the First World War have received renewed attention during the centenary commemorations. By exploring how the West Indian contribution is imagined in the media and creative arts, this paper problematizes the historical memory linking military service to citizenship in multicultural Britain. During the conflict, West Indian participation was used to suggest that the British Empire stood united in the face of German aggression. Through the 1920s and 1930s, the contribution of West Indian volunteers was recalled to support many political campaigns, including West Indian self-government and pan-African campaigns opposed to the Italian invasion of Ethiopia. Although West Indian soldiers were often excluded from combat roles, these movements relied on the rhetoric of masculine military sacrifice. Post-independence, West Indian nation states recalled imperial military service to affirm national identity. For the descendants of West Indian migrants in Britain, First World War military service may serve to underpin claims to equal citizenship. Government agencies and funding organizations have also turned to the West Indian war memory to increase community cohesion. The paper concludes that memories of belonging predicated on past military service are problematic. Non-combatant service may be overlooked and troubling histories avoided