研究了稀有的3 $d$电子重费米子体系LiV $_2$ O $_4$的低频自旋涨落动力学.发展了一个参数化的自洽重整化（SCR）理论，并应用于描述该材料中低$T$核自旋-晶格弛豫速率$1/T_1$的温度和压力依赖性.的实验数据$1/T_1$可下降到$\sim 1$ K的SCR理论很好地再现，显示AFM自旋波动的发展，作为顺磁性金属的方法在施加的压力下的磁不稳定性。在最高压力4.74 GPa下，在低于0.6 K时探测到的$1/T_1T$的低$T$峰被解释为由于LiV $_2$ O $_4$样品中磁性缺陷的自旋冻结引起的核自旋弛豫效应.
英文摘要：
Low frequency spin fluctuation dynamics in paramagnetic spinel LiV$_2$O$_4$, a rare 3$d$-electron heavy fermion system, is investigated. A parametrized self-consistent renormalization (SCR) theory of the dominant AFM spin fluctuations is developed and applied to describe temperature and pressure dependences of the low-$T$ nuclear spin-lattice relaxation rate $1/T_1$ in this material. The experimental data for $1/T_1$ available down to $\sim 1$K are well reproduced by the SCR theory, showing the development of AFM spin fluctuations as the paramagnetic metal approaches a magnetic instability under the applied pressure. The low-$T$ upturn of $1/T_1T$ detected below 0.6 K under the highest applied pressure of 4.74 GPa is explained as the nuclear spin relaxation effect due to the spin freezing of magnetic defects unavoidably present in the measured sample of LiV$_2$O$_4$.
We performed nuclear magnetic resonance (NMR) and muon spin relaxation (μSR) experiments to identify the magnetic ground state of the frustrated quantum A-site spinel, CuAl2O4. Our results verify that the ground state does not exhibit a long-range magnetic ordering, but a glass-like transition manifests at T*=2.3 K. However, the Gaussian shape and the weak longitudinal field dependence of μSR spectra below T* show that the ground state has dynamic spin fluctuations, distinct from those of conventional spin-glasses.
Charge ordering in the spinels AlV$_2$O$_4$ and LiV$_2$O$_4$
我们建立了尖晶石AlV $_2$ O $_4$和LiV $_2$ O $_4$（压力下）中电荷有序（CO）转变的微观理论。CO态的高度简并性通过与菱面体晶格变形的耦合而提升，菱面体晶格变形有利于过渡到具有分别形成Kagomé和三角平面的不等价V（1）和V（2）位的CO态。我们构造了一个包含形变势的扩展Hubbard型模型，该模型在无限制Hartree-Fock近似下处理，并正确地描述了观测到的CO一级跃迁.我们还讨论了相关轨道序的影响。此外，我们认为，由于不同的能带填充AlV $_2$ O $_4$应保持金属，而LiV $_2$ O $_4$在压力下应成为一个半导体时，电荷反作用集。
We report the structural and magnetic properties of a new system LiRhMnO$_{4}$ (LRMO) through x-ray diffraction, bulk magnetization, heat capacity and $^{7}$Li nuclear magnetic resonance (NMR) measurements. LRMO crystallizes in the cubic space group $\mathit{Fd}$$\bar{3}$$\mathit{m}$. From the DC susceptibility data, we obtained the Curie-Weiss temperature $\mathrmθ_{\mathrm{CW}}$ = -26 K and Curie constant $\mathit{C}$ = 1.79 Kcm$^{3}$/mol suggesting antiferromagnetic correlations among the magnetic Mn$^{4+}$ ions with an effective spin $\mathit{S}$ = $\frac{3}{2}$. At $\mathit{H}$ = 50 Oe, t…
Charge-spin-orbital Fluctuations in Mixed Valence Spinels: Comparative Study of AlV2O4 and LiV2O4
混合价尖晶石为几何阻挫晶格上强关联电子的电荷、自旋和轨道自由度之间的相互作用提供了一个肥沃的操场。其中，AlV $_2$ O $_4$和LiV $_2$ O $_4$表现出截然不同的令人困惑的行为：七格点团簇的自组织和重费米子行为。基于从头算得到的最大定域Wannier函数，建立了多带哈伯德模型，从理论上对这两种化合物的电荷-自旋-轨道涨落进行了比较研究.通过对广义极化率的本征模分析，我们发现在AlV $_2$ O $_4$中，相应的涨落出现在$σ$成键型轨道的电荷扇区.相反，在LiV $_2$ O $_4$中，$a_{\rm 1g}$轨道中的光学型自旋波动在低温下以无公度波数增强。从比较研究的影响进行了讨论的对比行为，包括金属-绝缘体的过渡压力下的LiV $_2$ O $_4$。
The mixed-valent spinel LiV$_{2}$O$_{4}$ is known as the first oxide heavy-fermion system. There is a general consensus that a subtle interplay of charge, spin, and orbital degrees of freedom of correlated electrons plays a crucial role in the enhancement of quasi-particle mass, but the specific mechanism has remained yet elusive. A charge-ordering (CO) instability of V$^{3+}$ and V$^{4+}$ ions that is geometrically frustrated by the V pyrochlore sublattice from forming a long-range CO down to $T$ = 0 K has been proposed as a prime candidate for the mechanism. To uncover the hidden CO instabil…
Heavy-Fermions in LiV2O4: Kondo-Compensation vs. Spin-Liquid Behavior?
在金属尖晶石LiV 2 O 4中进行7 Li NMR测量。在30 mK < T < 280 K的温度范围内，研究了线宽、Knight位移和自旋-晶格弛豫速率的温度依赖性。对于温度T < 1 K，我们观察到自旋晶格弛豫速率以指数方式减慢。NMR结果可以用自旋液体行为和0.6K量级的自旋能隙的打开来解释。
Crystallography, magnetic susceptibility, heat capacity, and electrical resistivity of heavy fermion LiV$_2$O$_4$ single crystals grown using a self-flux technique
LiV$_2$O$_4$ spinel is known to exhibit heavy fermion-like behavior below a characteristic temperature $T_K\simeq 20$ K, while it preserves a paramagnetic state down to $T\sim10^{-2}$ K due to geometrical frustration. Here, it is shown that the dynamical spin susceptibility $χ({\bf q},ω)$ in LiV$_2$O$_4$ exhibits anomalous duality which is modeled as a sum of itinerant ($χ_{\rm F}$) and local ($χ_{\rm L}$) components,and that the local spin dynamics inferred from $χ_{\rm L}({\bf q},ω)$ is qualitatively different from that expected from time-averaged bulk properties. The anomaly coexists with t…
Thermodynamic properties, $^{31}$P nuclear magnetic resonance (NMR) measurements, and density-functional band-structure calculations for $\varepsilon$-LiVOPO$_4$ are reported. This quantum magnet features a singlet ground state and comprises two types of alternating spin-$\frac12$ chains that manifest themselves by the double maxima in the susceptibility and magnetic specific heat, and by the two-step magnetization process with an intermediate $\frac12$-plateau. From thermodynamic data and band-structure calculations, we estimate the leading couplings of $J_1\simeq 20$ K and $J_2\simeq 60$ K a…
