Cr$_{3+δ}$Te$_4$中竞争的磁相在空间上分离
Competing magnetic phases in Cr$_{3+δ}$Te$_4$ are spatially segregated
AI总结：
Cr$_{3+δ}$Te$_4$中存在两种空间分离的磁相，铁磁和反铁磁相在不同温度下有序，研究揭示了其晶格结构和应变对磁序的影响。
摘要：
Cr$_{1+x}$Te$_2$是一种自插入的vdW系统，因其室温铁磁相和可调拓扑性质而备受关注。早期对单斜相Cr$_3$Te$_4$（x=0.5）的中子衍射测量提供了铁磁和反铁磁相竞争的证据。在这里，我们对Cr$_{3+δ}$Te$_4$（δ=-0.10）单晶应用中子衍射，发现其由两种不同的单斜相组成，一种在T_C≈321 K以下具有铁磁序，另一种在T_N≈86 K以下发展出反铁磁序。相比之下，δ=-0.26的晶体仅表现出铁磁序。单晶分析还通过中子衍射、XPD和TEM测量结果得到补充。从T_C和T_N处观察到的自发磁致伸缩的相反符号，以及TEM证据显示单个薄（约100 nm）晶粒中存在两种单斜相，我们得出结论，这两种相必须具有细晶（<100 nm）的互层特征，这可能发生在生长过程中高温分相时。通过DFT计算放松的晶格结构，为观察到的自发磁致伸缩提供了解释。磁矩的大小和方向与晶格参数变化的相关性表明，磁序对应变敏感，从而解释了为什么在薄膜样品中，磁序温度和各向异性可能与块体样品不同，当后者受应变影响时。我们的结果指出，需要研究Cr$_{1+x}$Te$_2$系统中报告的所谓共存的铁磁和反铁磁相，如Cr$_5$Te$_8$相（x=0.25）.
英文摘要：
Cr$_{1+x}$Te$_2$ is a self-intercalated vdW system that is of current interest for its room-temperature FM phases and tunable topological properties. Early NPD measurements on the monoclinic phase Cr$_3$Te$_4$ ($x=0.5$) presented evidence for competing FM and AFM phases. Here we apply neutron diffraction to a single crystal of Cr$_{3+δ}$Te$_4$ with $δ=-0.10$ and discover that it consists of two distinct monoclinic phases, one with FM order below $T_{\rm C} \approx 321$ K and another that develops AFM order below $T_{\rm N} \approx 86$ K. In contrast, we find that a crystal with $δ=-0.26$ exhibits only FM order. The single-crystal analysis is complemented by results obtained with NPD, XPD, and TEM measurements on the $δ=-0.10$ composition. From observations of spontaneous magnetostriction of opposite sign at $T_{\rm C}$ and $T_{\rm N}$, along with the TEM evidence for both monoclinic phases in a single thin ($\approx$ 100 nm) grain, we conclude that the two phases must have a fine-grained ($\lesssim$ 100 nm) intergrowth character, as might occur from high-temperature spinodal decomposition during the growth process. Calculations of the relaxed lattice structures for the FM and AFM phases with DFT provide a rationalization of the observed spontaneous magnetostrictions. Correlations between the magnitude and orientation of the magnetic moments with lattice parameter variation demonstrate that the magnetic orders are sensitive to strain, thus explaining why magnetic ordering temperatures and anisotropies can be different between bulk and thin-film samples, when the latter are subject to epitaxial strain. Our results point to the need to investigate the supposed coexistence FM and AFM phases reported elsewhere in the Cr$_{1+x}$Te$_2$ system, such as in the Cr$_5$Te$_8$ phase ($x=0.25$).
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