AI 中文总结
本研究通过分子束外延结合后退火技术，在单晶Cr-NbSe₂中独立调控载流子浓度与磁矩几何构型，实验厘清了二者对RKKY磁性的影响，实现了载流子可调的RKKY磁性，该方法可推广至插层过渡金属二硫族化合物体系。
AI 中文摘要
在由Ruderman-Kittel-Kasuya-Yosida（RKKY，鲁德曼-基特尔-粕谷-芳田）相互作用主导的巡游磁体中，交换耦合同时取决于磁矩间距$r$和费米波矢$k_{\text{F}}$，但在块体合成中二者紧密耦合：成分变化通常会同时改变这两个参数。本研究采用薄膜方法，在单晶基质中独立调控这两个变量。利用分子束外延（MBE）技术，我们通过不同的生长窗口，在同一NbSe₂基质中制备出$2\times2\rm{R}0^\text{o}$ Cr$_{1/4}$NbSe₂和$\rm{\r{3}}\times\r{3}R30^\text{o}$ Cr$_{1/3}$NbSe₂两种结构。随后在一系列温度下进行可控的生长后退火，在结构转变阈值以下保持Cr超结构不变的同时，调控载流子浓度。两种生长态相在电子结构、磁基态和输运性质上存在差异。在该退火序列中，霍尔响应呈现系统性演化，而磁响应的变化则对结构不敏感：仅在临界退火温度以上，相同$\rm{\r{3}}\times\r{3}R30^\text{o}$结构类别中才会出现铁磁有序，从实验上厘清了载流子浓度与磁矩几何构型的关联。霍尔效应的幅值和符号演化表明，该体系属于低载流子浓度体系，其$k_{\text{F}}$易受适度外调的影响。因此，Cr-NbSe₂在单晶基质中实现了载流子敏感的RKKY磁性，这种“MBE+退火”的方法可推广至插层过渡金属二硫族化合物家族。
英文摘要
In itinerant magnets governed by the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction, the exchange coupling depends on both the moment-moment distance $r$ and the Fermi wavevector $k_{\mathrm{F}}$, yet in bulk synthesis the two are tightly coupled: a change in composition typically alters both. Here, we use a thin-film approach to tune these two variables independently in a single crystalline host. Using molecular-beam epitaxy (MBE), we stabilize either $2\times2\mathrm{R}0^\circ$ Cr$_{1/4}$NbSe$_2$ or $\sqrt{3}\times\sqrt{3}\mathrm{R}30^\circ$ Cr$_{1/3}$NbSe$_2$ within the same NbSe$_2$ host through separate growth windows. Controlled post-growth annealing performed across a series of temperatures then modifies the carrier density while leaving the Cr superstructure intact below a structural-transition threshold. The two as-grown phases are distinct in electronic structure, magnetic ground state, and transport. Along this annealing series, the Hall response evolves systematically while the magnetic response changes in a structurally insensitive manner, with ferromagnetic order emerging within the same $\sqrt{3}\times\sqrt{3}\mathrm{R}30^\circ$ structural class only above a critical annealing temperature, experimentally disentangling carrier density and moment geometry. The Hall magnitude and sign evolution point to a low-carrier-density system in which $k_{\mathrm{F}}$ is susceptible to modest external tuning. Cr-NbSe$_2$ thus realizes carrier-sensitive RKKY magnetism in a single crystalline host, within an MBE-plus-annealing approach extensible across the intercalated transition-metal dichalcogenide family.
Comments12 pages, 5 figures; Supplemental Material: 12 pages, 11 figures, 1 table
