反铁四极系统TmGa_{3}单重态基态的晶体场非弹性中子谱研究
Singlet ground state probed by crystal field inelastic neutron spectroscopy on the antiferroquadrupolar system TmGa_{3}
摘要：
TmGa $_{3}$（AuCu $_3$结构）经历了两个相变，即在$\sim$ 4.29 K的反铁四极相变和在$\sim$ 4.26 K的长程反铁磁有序化.由于两个相变的紧密邻近，TmGa $_3$提供了一个有趣的系统来研究电荷和磁自由度的相互作用。为了理解这种相互作用，我们进行了非弹性中子散射实验TmGa $_{3}$在顺磁制度（$T >$ 5 K），以重新确定晶体电场水平计划。通过拟合不同温度下的光谱，我们获得了新的晶场能级方案，其中Lea、Leask和Wolf参数为$x_{\rm LLW}$ = -0.44（2）和$W$ = -0.222（2）K。在5 K的总晶场分裂金额为$\sim$ 2.3 meV，约一个数量级小于以前发现的，但在良好的协议与分裂外推从相关的ErGa $_3$系统。我们的分析产生了一个$Γ_{2}$的单作为晶体场基态紧接着由一个（正）$Γ_{1}$单在0.009 meV。下一个激发态是在$\sim$ 0.5 meV的$Γ_{5}^{(2)}$三重态，其几乎简并为$Γ_{4}$二重态。这一水平方案与以前的研究结果相反。随后分析的磁化沿几个结晶方向和温度依赖的磁化率以及磁贡献的比热是符合我们的新的晶场参数。反铁四极和反铁磁过渡的影响进行了讨论。
英文摘要：
TmGa$_{3}$ (AuCu$_3$ structure) undergoes two phase transitions, an antiferroquadrupolar transition at $\sim$ 4.29 K and long-range antiferromagnetic ordering at $\sim$ 4.26 K. Due to the close vicinity of the two phase transitions, TmGa$_3$ offers an interesting system to study the interplay of charge and magnetic degrees of freedom. In order to understand this interplay we have performed inelastic neutron scattering experiments on TmGa$_{3}$ in the paramagnetic regime ($T >$ 5 K) to redetermine the crystal electric field level scheme. By fitting our spectra at various temperatures we obtain a new crystal field level scheme with Lea, Leask and Wolf parameters of $x_{\rm LLW}$ = -0.44(2) and $W$ = -0.222(2) K. The total crystal field splitting at 5K amounts to $\sim$ 2.3 meV, about an order of magnitude less than found previously, but in good agreement with the splitting extrapolated from the related ErGa$_3$ system. Our analysis yields a $Γ_{2}$ singlet as the crystal field ground state followed closely by a (nonmagnetic) $Γ_{1}$ singlet at 0.009 meV. The next excited states are a $Γ_{5}^{(2)}$ triplet at $\sim$0.5 meV, which is almost degenerate to a $Γ_{4}$ doublet. This level scheme is adverse to previous findings. Subsequent analysis of the magnetisation along several crystallographic directions and the temperature dependant susceptibility as well as of the magnetic contribution to the specific heat are consistent with our new crystal field parameters. Implications for the antiferroquadrupolar and the antiferromagnetic transition are discussed.
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