标题： Co$_x$NbSe$_2$单晶中公度与非公度反铁磁基态的共存 显示英文标题

标题： Coexistence of Commensurate and Incommensurate Antiferromagnetic Groundstates in Co$_x$NbSe$_2$ Single Crystal

摘要： 在Co$_x$NbSe$_2$中，晶体对称性以及钴位点占据驱动了两种不同磁性相的形成。 在 $x = 1/4$时，反演对称结构 ($P$6$_3$/$mmc$) 促进了 Co-Co 相互作用，导致一种 $A$-型反铁磁结构相的形成，其相变温度为 $T_N^A$ = 169 K。而在 $x = 1/3$时，非反演对称结构 ($P$6$_3$22) 引发了低温磁性相，其相变温度为 $T_N^S$ = 28 K。我们报道了这两种亚结构在一个超晶格中共存，相对于基质晶格，其核传播矢量为 (1/3, 1/3, 0)。 Co$_{0.28}$NbSe$_2$单晶表现出两种磁性转变，其中$T_N^A$对应于$x \sim 1/4$相，$T_N^S$对应于$x \sim 1/3$相。磁化率和比热测量证实了这些转变，尽管只有高温$T_N^A$相显著影响电阻率。 我们成功地从粉末样品中分离出每一相，而插层比为$x = 0.28$的单晶在单一样品中显示出两相共存。 利用单晶中子衍射，我们解析了高温中心对称相（$T_N^A$）的磁结构，而中子粉末衍射揭示了低温非中心对称相（$T_N^S$）的双$q$磁结构。 显示英文摘要

摘要： In Co$_x$NbSe$_2$, crystal symmetry, and cobalt site occupation drive the formation of two distinct magnetic phases. At $x = 1/4$, the centrosymmetric structure ($P$6$_3$/$mmc$) promotes Co-Co interactions leading to the formation of an $A$-type antiferromagnetic structure phase with a transition temperature of $T_N^A$ = 169 K. At $x = 1/3$, the non-centrosymmetric structure ($P$6$_3$22) induces a lower-temperature magnetic phase with $T_N^S$ = 28 K. We report the coexistence of both substructures within a superlattice, with a nuclear propagation vector of (1/3, 1/3, 0) relative to the host lattice. Single crystals of Co$_{0.28}$NbSe$_2$ exhibit both magnetic transitions, with $T_N^A$ corresponding to the $x \sim 1/4$ phase and $T_N^S$ corresponding to the $x \sim 1/3$ phase. Magnetic susceptibility and specific heat measurements confirm these transitions, although only the high-temperature $T_N^A$ phase significantly affects resistivity. We successfully isolate each phase in powder samples, while single crystals with an intercalation ratio of $x = 0.28$ display the coexistence of both phases in a single sample. Using single-crystal neutron diffraction, we solved the magnetic structure of the high-temperature centrosymmetric phase ($T_N^A$), and neutron powder diffraction revealed the double-$q$ magnetic structure of the low-temperature noncentrosymmetric phase ($T_N^S$)