发表机构
Institute of Geophysics of the Czech Academy of Sciences; Faculty of Nuclear Sciences and Physical Engineering, Czech Technical University; Faculty of Mathematics and Physics, Charles University（捷克科学院地球物理研究所; 捷克理工大学核科学与物理工程学院; 查理大学数学与物理学院）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本研究通过DFT结合微扰理论计算方解石族碳酸盐的抗磁磁化率及各向异性，并模拟Fe/Mn掺杂的顺磁贡献，发现各向异性主要由轨道磁化主导，为定量解释AMS提供了本征参考值。
AI 中文摘要
磁化率各向异性（AMS）是推断岩石组构的广泛使用工具，然而定量解释受限于造岩矿物单晶磁性质数据的稀缺，以及难以将本征抗磁性杂质相关磁性分离。本文采用密度泛函理论（DFT）结合微扰理论，计算了方解石族碳酸盐（方解石、菱镁矿和白云石）的抗磁磁化率及AMS，并量化了过渡金属掺杂带来的额外顺磁贡献。对于纯方解石，计算得到的磁化率及其各向异性与已发表的单晶测量结果吻合良好，验证了从头计算方法在抗磁相中的适用性。我们为菱镁矿和白云石提供了改进的本征抗磁参考值，这两种矿物的实验磁化率通常受磁性杂质影响。为显式处理杂质效应，我们使用超胞模拟方解石中Fe和Mn的替代。计算的自旋矩再现了预期的高自旋态（Fe$^{2+}$，$S=2$；Mn$^{2+}$，$S=5/2$），并得到与实验斜率匹配的每Fe浓度磁化率各向异性。强各向异性主要由与晶体学$c$轴相关的轨道贡献主导，而非自旋-轨道耦合，这凸显了轨道磁化强度作为模拟碳酸盐顺磁AMS的关键但数值上具有挑战性的要素。
英文摘要
The anisotropy of magnetic susceptibility (AMS) is a widely used tool to infer rock fabrics, yet quantitative interpretation is limited by sparse single-crystal magnetic properties for rock-forming minerals and by the difficulty of separating intrinsic diamagnetism from impurity-related magnetism. Here we use density-functional theory (DFT) combined with perturbation theory to compute the diamagnetic susceptibility and AMS of calcite-group carbonates (calcite, magnesite, and dolomite) and to quantify the additional paramagnetic contribution from transition-metal doping. For pure calcite, the calculated susceptibility and its anisotropy are in good agreement with published single-crystal measurements, validating the ab initio approach for diamagnetic phases. We provide improved intrinsic diamagnetic reference values for magnesite and dolomite, for which experimental susceptibilities are commonly affected by magnetic impurities. To address impurity effects explicitly, we model Fe and Mn substitution in calcite using supercells. The computed spin moments reproduce expected high-spin states (Fe$^{2+}$, $S=2$; Mn$^{2+}$, $S=5/2$) and yield a susceptibility anisotropy per Fe concentration that matches the experimental slope. The strong anisotropy is primarily governed by an orbital contribution tied to the crystallographic $c$-axis rather than by spin-orbit coupling, highlighting orbital magnetisation as a key but numerically challenging ingredient for modelling of paramagnetic AMS in carbonates.
