$^{77}$ Se NMR探测的磁电化合物Cu $_2$ OSeO PDMATHAAC的铁磁性
Ferrimagnetism of the magnetoelectric compound Cu$_2$OSeO$_3$ probed by $^{77}$Se NMR
摘要：
我们提出了一个彻底的$^{77}$硒核磁共振研究的磁电化合物铜$_2$ OSeO $_3$的单晶。从NMR数据中提取的局部电子矩的温度依赖性与从高T顺磁相到低T亚铁磁态的磁相变完全一致，其中3/4的Cu $^{2+}$离子平行排列，1/4反平行于14.09 T的外加场排列。过渡到这个3up-1down磁状态是不伴随着任何分裂的NMR线或任何突然的修改，在其扩大，因此没有观察到的减少从其高T立方\textit{P} 2 $_1$ 3空间群的晶体对称性。这些结果与Bos { \it等人}先前报道的粉末样品的高分辨率X射线衍射和磁化数据一致。[Phys. Rev. B，{PDMATHAMT 78}，094416（2008）]。我们还开发了一个平均场理论描述的问题的基础上，一个反铁磁（$J_\text{afm}\simeq 68$ K）和一个铁磁（$J_\text{fm}\simeq -50$ K）最近邻交换相互作用的微观自旋哈密顿量。
英文摘要：
We present a thorough $^{77}$Se NMR study of a single crystal of the magnetoelectric compound Cu$_2$OSeO$_3$. The temperature dependence of the local electronic moments extracted from the NMR data is fully consistent with a magnetic phase transition from the high-T paramagnetic phase to a low-T ferrimagnetic state with 3/4 of the Cu$^{2+}$ ions aligned parallel and 1/4 aligned antiparallel to the applied field of 14.09 T. The transition to this 3up-1down magnetic state is not accompanied by any splitting of the NMR lines or any abrupt modification in their broadening, hence there is no observable reduction of the crystalline symmetry from its high-T cubic \textit{P}2$_1$3 space group. These results are in agreement with high resolution x-ray diffraction and magnetization data on powder samples reported previously by Bos {\it et al.} [Phys. Rev. B, {\bf 78}, 094416 (2008)]. We also develop a mean field theory description of the problem based on a microscopic spin Hamiltonian with one antiferromagnetic ($J_\text{afm}\simeq 68$ K) and one ferromagnetic ($J_\text{fm}\simeq -50$ K) nearest-neighbor exchange interaction.
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