Laboratory of Crystallography, University of Bayreuth, 95440 Bayreuth, Germany.
Phys Chem Chem Phys. 2018 Oct 7;20(37):24465-24476. doi: 10.1039/c8cp03761b. Epub 2018 Sep 17.
High-pressure single-crystal X-ray diffraction at ambient temperature and high-pressure SQUID measurements down to 2 K were performed up to ∼2.5 GPa on ammonium metal formates, [NH][M(HCOO)] where M = Mn, Fe, and Ni, in order to correlate structural variations to magnetic behaviour. Similar structural distortions and phase transitions were observed for all compounds, although the transition pressures varied with the size of the metal cation. The antiferromagnetic ordering in [NH][M(HCOO)] compounds was maintained as a function of pressure, and the magnetic ordering transition temperature changed within a few kelvins depending on the structural distortion and the metal cation involved. These compounds, in particular [NH][Fe(HCOO)], showed greatest sensitivity to the degree of spin canting upon compression, clearly visible from the twenty-fold increase in the low-temperature magnetisation for [NH][Fe(HCOO)] at 1.4 GPa, and the change from purely antiferromagnetic to weakly ferromagnetic ordering in [NH][Mn(HCOO)] at 1 GPa. The variation in the exchange couplings and spin canting was checked with density-functional calculations that reproduce well the increase in canted moment within [NH][Fe(HCOO)] upon compression, and suggest that the Dzyaloshinskii-Moriya (DM) interaction is evolving as a function of pressure. The pressure dependence of spin canting is found to be highly dependent on the metal cation, as magnetisation magnitudes did not change significantly for when M = Ni or Mn. These results demonstrate that the overall magnetic behaviour of each phase upon compression was not only dependent on the structural distortions but also on the electronic configuration of the metal cation.
在环境温度和高达 2 K 的高压 SQUID 测量下，对[NH][M(HCOO)]（其中 M = Mn、Fe 和 Ni）的铵金属甲酸盐进行了高压单晶 X 射线衍射，以将结构变化与磁行为相关联。尽管转变压力随金属阳离子的大小而变化，但所有化合物都观察到相似的结构变形和相变。[NH][M(HCOO)]化合物中的反铁磁有序随着压力的增加而保持，磁有序转变温度在几开尔文范围内变化，具体取决于结构变形和涉及的金属阳离子。这些化合物，特别是[NH][Fe(HCOO)]，在压缩时对自旋倾斜的程度表现出最大的敏感性，从[NH][Fe(HCOO)]在 1.4 GPa 时低温磁化强度增加二十倍，以及[NH][Mn(HCOO)]在 1 GPa 时从纯反铁磁到弱铁磁有序的转变中可以清楚地看到。用密度泛函计算检查了交换耦合和自旋倾斜的变化，该计算很好地再现了[NH][Fe(HCOO)]在压缩时倾斜矩的增加，并表明 Dzyaloshinskii-Moriya (DM) 相互作用随着压力的变化而演变。发现自旋倾斜的压力依赖性高度依赖于金属阳离子，因为当 M = Ni 或 Mn 时，磁化强度没有明显变化。这些结果表明，每个相在压缩时的整体磁行为不仅取决于结构变形，还取决于金属阳离子的电子构型。
