Dubroca Thierry, Wang Xiaoling, Mentink-Vigier Frédéric, Trociewitz Bianca, Starck Matthieu, Parker David, Sherwin Mark S, Hill Stephen, Krzystek J
National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL 32310, USA.
National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL 32310, USA; Center for Molecular Magnetic Quantum Materials, University of Florida, Gainesville, FL 32611, USA.
J Magn Reson. 2023 Aug;353:107480. doi: 10.1016/j.jmr.2023.107480. Epub 2023 May 19.
Electron Paramagnetic Resonance (EPR) is a powerful technique to study materials and biological samples on an atomic scale. High-field EPR in particular enables extracting very small g-anisotropies in organic radicals and half-filled 3d and 4f metal ions such as Mn (3d) or Gd (4f), and resolving EPR signals from unpaired spins with very close g-values, both of which provide high-resolution details of the local atomic environment. Before the recent commissioning of the high-homogeneity Series Connected Hybrid magnet (SCH, superconducting + resistive) at the National High Magnetic Field Laboratory (NHMFL), the highest-field, high-resolution EPR spectrometer available was limited to 25 T using a purely resistive "Keck" magnet at the NHMFL. Herein, we report the first EPR experiments performed using the SCH magnet capable of reaching the field of 36 T, corresponding to an EPR frequency of 1 THz for g = 2. The magnet's intrinsic homogeneity (25 ppm, that is 0.9 mT at 36 T over 1 cm diameter, 1 cm length cylinder) was previously established by NMR. We characterized the magnet's temporal stability (5 ppm, which is 0.2 mT at 36 T over one-minute, the typical acquisition time) using 2,2-diphenyl-1-picrylhydrazyl (DPPH). This high resolution enables resolving the weak g-anisotropy of 1,3-bis(diphenylene)-2-phenylallyl (BDPA), Δg = 2.5 × 10 obtained from measurements at 932 GHz and 33 T. Subsequently, we recorded EPR spectra at multiple frequencies for two Gd complexes with potential applications as spin labels. We demonstrated a significant reduction in line broadening in Gd[DTPA], attributed to second order zero field splitting, and a resolution enhancement of g-tensor anisotropy for Gd[sTPATCN]-SL.
电子顺磁共振（EPR）是一种在原子尺度上研究材料和生物样品的强大技术。特别是高场EPR能够提取有机自由基以及半充满的3d和4f金属离子（如Mn（3d）或Gd（4f））中非常小的g-各向异性，并分辨来自具有非常接近g值的未成对自旋的EPR信号，这两者都提供了局部原子环境的高分辨率细节。在国家高磁场实验室（NHMFL）最近启用高均匀性串联混合磁体（SCH，超导+电阻）之前，可用的最高场、高分辨率EPR光谱仪使用NHMFL的纯电阻“凯克”磁体时仅限于25 T。在此，我们报告了首次使用能够达到36 T磁场的SCH磁体进行的EPR实验，对于g = 2，该磁场对应于1 THz的EPR频率。该磁体的固有均匀性（25 ppm，即在36 T下，直径1 cm、长度1 cm的圆柱体上为0.9 mT）先前已通过核磁共振确定。我们使用2,2-二苯基-1-苦基肼基（DPPH）表征了磁体的时间稳定性（5 ppm，即在36 T下，在典型采集时间一分钟内为0.2 mT）。这种高分辨率能够分辨出1,3-双（二亚苯基）-2-苯基烯丙基（BDPA）的弱g-各向异性，Δg = 2.5×10，这是在932 GHz和33 T下测量得到的。随后，我们记录了两种具有作为自旋标记潜在应用的Gd配合物在多个频率下的EPR光谱。我们证明了Gd[DTPA]中线宽的显著减小，这归因于二阶零场分裂，以及Gd[sTPATCN]-SL的g张量各向异性分辨率的提高。
