论文标题
pbfe $ _ {1/2} $ nb $ _ {1/2} $ o $ $ $ _ {3} $中的快速宽带群集旋转玻璃动力学
Fast broadband cluster spin-glass dynamics in PbFe$_{1/2}$Nb$_{1/2}$O$_{3}$
论文作者
论文摘要
pbfe $ _ {1/2} $ nb $ _ {1/2} $ o $ _ {3} $（pfn）是一个放松器铁电机（t $ _ {c} $ _ {c} $ \ sim $ 400 k），由无序的磁性fe $^{3+} $（s = $} $^$ {5 \ py a $^$ {5 \ py a py a） ````聚集玻璃''阶段（W. Kleemann $ \ textit {et al。} $phys。Rev。lett。$ {\ bf {\ bf {105}} $，257202（2010）。我们将中子散射用于调查该阶段的动态磁法，在大型单晶中显示出低温旋转玻璃的过渡（$ 15在空间上，抗磁磁性阶段的静态响应（在我们的分辨率设置的时间尺度上采样）的特征是平均磁性旋转方向，这些方向缺乏任何首选方向，而驱动该相的动力学是由逐渐增加的50 k逐渐增加的。冷却，从而弄清磁性，直到低温玻璃相设置为t $ _ {g} $ $ \ sim $ 15 k $ 15 k。中子光谱用于表征群集玻璃相中的自旋波动，并被发现由$ \ sim $ the的频率宽带定义，在这里定义了$ \ sim $ the的规模，在此期间termed。驱动磁性波动的频率带宽模拟相关长度并降低到$ \ sim $ 50 K，然后再次增加直至玻璃过渡。通过研究低能声音子，我们找到了构成簇的基础的多个不同结构区域的证据，产生了大量的局部疾病。我们建议，源自簇之间的相互作用的随机分子场对于破坏磁性和最终形成了PFN中的群集玻璃很重要。
PbFe$_{1/2}$Nb$_{1/2}$O$_{3}$ (PFN) is a relaxor ferroelectric (T$_{c}$ $\sim$ 400 K) consisting of disordered magnetic Fe$^{3+}$ (S=${5\over2}$, L$\approx$0) ions resulting in a low temperature ``cluster glass" phase (W. Kleemann $\textit{et al.}$ Phys. Rev. Lett. ${\bf{105}}$, 257202 (2010)). We apply neutron scattering to investigate the dynamic magnetism of this phase in a large single crystal which displays a low temperature spin glass transition (T$_{g} \sim$ 15 K), but no observable spatially long-range antiferromagnetic order. The static response in the cluster glass phase (sampled on the timescale set by our resolution) is found to be characterized by an average magnetic spin direction that lacks any preferred direction. The dynamics that drive this phase are defined by a magnetic correlation length that gradually increases with decreasing temperature. However, below $\sim$ 50 K the spatial correlations gradually becoming more short range indicative of increasing disorder on cooling, thereby unravelling magnetism, until the low temperature glass phase sets in at T$_{g}$ $\sim$ 15 K. Neutron spectroscopy is used to characterize the spin fluctuations in the cluster glass phase and are found to be defined by a broadband of frequencies on the scale of $\sim$ THz, termed here ``fast" fluctuations. The frequency bandwidth driving the magnetic fluctuations mimics the correlation length and decreases until $\sim$ 50 K, and then increases again until the glass transition. Through investigating the low-energy acoustic phonons we find evidence of multiple distinct structural regions which form the basis of the clusters, generating a significant amount of local disorder. We suggest that random molecular fields originating from conflicting interactions between clusters is important for the destruction of magnetic order and the eventual formation of the cluster glass in PFN.
