Smirnova Ekaterina S, Frolov Kirill V, Sidorova Ekaterina V, Sorokin Timofei A, Alekseeva Olga A, Guskov Anton V, Gagarin Pavel G, Gudim Irina A
Shubnikov Institute of Crystallography of National Research Centre `Kurchatov Institute', Moscow 119333, Russian Federation.
Kurnakov Institute of General and Inorganic Chemistry RAS, Moscow 119071, Russian Federation.
Acta Crystallogr B Struct Sci Cryst Eng Mater. 2025 Feb 1;81(Pt 1):69-83. doi: 10.1107/S2052520624011569. Epub 2024 Dec 23.
The crystal structures and hyperfine magnetic parameters of EuFe(BO) and mixed EuLaFe(BO) were studied over a wide temperature range in order to analyze correlations of the structural and magnetic features and the phase transitions in multiferroic compounds of the rare-earth iron borate family. The chemical compositions of the crystals are reported from X-ray fluorescence analysis. The crystal structures of EuFe(BO) and EuLaFe(BO) were determined using single-crystal X-ray diffraction in the temperature range 25-500 K. A structural phase transition is observed in EuFe(BO) below 89 K which is related to distortions in the interatomic distances and angles. The most significant of which are for R-O, R-B, R-Fe, Fe-O and Fe-Fe distances, and the angles between the BO triangles and the ab plane. There is no structural phase transition in lanthanum-doped EuFe(BO) based on specific heat measurements (2.2-101.3 K) and structure analysis (25-500 K), and the temperature dependences of the interatomic distances and angles are smooth. The lengths of the superexchange paths needed for the appearance of a structural phase transition in RFe(BO) have been proposed. Negative thermal expansion is observed for both compounds below 90 K, resulting from a growth of the interatomic Fe-Fe distances in the iron chains during cooling. The largest atomic displacement parameters are observed for O atoms (O2), indicating that they have the highest mobility. The magnetic properties of EuFe(BO) and EuLaFe(BO) were analyzed using Mössbauer spectroscopy in the temperature range 4.5-298 K. Néel temperatures (T) of 34.57 (1) and 32.22 (1) K are obtained based on Mössbauer spectroscopy for the pure and doped crystals, respectively. The maximum specific heat capacity temperature dependence related to the magnetic phase transition for the doped crystal is observed at 31.2 K. A violation of the strict arrangement of antiferromagnetic ordering in the ab plane in the La-doped crystals at low temperatures is suggested. The magnetic contributions of the two structural positions of the iron ions to the Mössbauer spectra could not be distinguished in either pure and doped compounds, regardless of whether they are in the paramagnetic and antiferromagnetic regions.
研究了EuFe(BO)和混合EuLaFe(BO)在很宽温度范围内的晶体结构和超精细磁参数，以分析稀土铁硼酸盐家族多铁性化合物的结构和磁特性以及相变之间的相关性。通过X射线荧光分析报告了晶体的化学成分。在25 - 500 K温度范围内使用单晶X射线衍射确定了EuFe(BO)和EuLaFe(BO)的晶体结构。在89 K以下的EuFe(BO)中观察到结构相变，这与原子间距离和角度的畸变有关。其中最显著的是R - O、R - B、R - Fe、Fe - O和Fe - Fe距离，以及BO三角形与ab平面之间的角度。基于比热测量(2.2 - 101.3 K)和结构分析(25 - 500 K)，掺镧的EuFe(BO)中没有结构相变，原子间距离和角度的温度依赖性是平滑的。提出了RFe(BO)中出现结构相变所需的超交换路径长度。在90 K以下的两种化合物中均观察到负热膨胀，这是由于冷却过程中铁链中原子间Fe - Fe距离的增加所致。对于O原子(O2)观察到最大的原子位移参数，表明它们具有最高的迁移率。在4.5 - 298 K温度范围内使用穆斯堡尔谱分析了EuFe(BO)和EuLaFe(BO)的磁性能。基于穆斯堡尔谱，分别得到纯晶体和掺杂晶体的奈尔温度(T)为34.57 (1)和32.22 (1) K。在31.2 K观察到掺杂晶体中与磁相变相关的最大比热容量温度依赖性。有人提出，在低温下掺镧晶体的ab平面中反铁磁有序的严格排列受到破坏。无论处于顺磁和反铁磁区域，在纯化合物和掺杂化合物中都无法区分铁离子两个结构位置对穆斯堡尔谱的磁贡献。
