六角铁氧体中电偶极几何阻挫系统的多场调控

Frustration has attracted much attention due to the resulting exotic properties in solids. Especially, the geometric frustration systems can lead to a large degeneracy of the ground state, together with the existence of quantum fluctuation, resulting in many strange quantum states. Thus, it becomes one of the important subjects in term of condensed matter physics. However, most of the experimental verification of the theoretical predictions have been mostly focused on the magnetic material only. In this project, based on the similarity of Hamiltonian between the Ising spin system and electric-dipole system and previous studies by the candidate, the frustrated 2D triangular electric-dipole antiferroelectric system in M-type hexaferrite is chosen to be studied. We plan to prepare the isotope doped sample as the starting specimen and make use of high pressure, electric field and magnetic field as the tuning parameters to study the ground states and quantum phase transition of 2D frustrated triangular lattice under different extent of quantum fluctuation. In doing so, the multi-fields tuning of quantum critical behaviors are expected to be realized. Eventually, this study is expected to reveal the phase diagram of the frustrated 2D triangular electric-dipole antiferroelectric system around the quantum critical point, the universality class of the quantum critical behavior, and the similarities and differences between the electric-dipole frustrated system and the corresponding magnetic systems.

阻挫常常在材料中产生很多奇异的性质而引起了广泛的关注。特别是在磁几何阻挫系统中强烈的基态简并、量子涨落的存在，可以导致非常丰富的量子物态，使得磁几何阻挫体系成为凝聚态物理研究领域的一个重要分支。但是对于磁几何阻挫理论模型的实验验证都局限于磁性材料本身。本项目基于磁性Ising自旋体系与电偶极体系在哈密顿量数学形式上的类似性，结合申请人前期的研究，拟选取M型六角铁氧体中新发现的二维反铁电三角格子电偶极几何阻挫系统为研究对象，采用同位素替换为样品制备手段，高压及电场、磁场为主要调控手段，研究二维三角格子反铁电阻挫系统在不同量子涨落下的基态及相关量子相变，进而实现多外场对量子临界行为的调控，最终揭示二维三角格子反铁电电偶极系统量子临界点附近的相图、量子临界行为的普适性类型及其与磁性几何阻挫系统间的异同。

阻挫常常在材料中产生很多奇异的性质而引起了广泛的关注。特别是在磁几何阻挫系统中强烈的基态简并、量子涨落的存在，可以导致非常丰富的量子物态，使得磁几何阻挫体系成为凝聚态物理研究领域的一个重要分支。本研究选取了六角铁氧体及其它一些由磁结构或者磁性离子引起电耦极距的单相多铁体系，采用单晶、多晶和同位素替换为样品制备手段，高压及电场、磁场为主要调控手段，研究电偶极阻挫及近阻挫系统在不同涨落、外场下的行为。取得的主要成果包括：1）利用高压退火炉，制备了一系列18O的同位素掺杂的单晶M型六角铁氧体BaFe12O19样品。利用不同比例掺杂的57Fe制备了一系列高质量BaM型多晶样品。2）通过介电、铁电等手段确定这些样品中，O同位素掺杂对体系的量子顺电行为没有任何作用，排除了FeO5双金字塔单元中Fe3+离子与周围的O之间的电子轨道杂化。3）测量了57Fe系列掺杂样品的XRD、介电等性质，同时结合频率的改变等其它手段，出乎意料的发现在二维三角格子反铁电电偶极系统量子临界点附近有缓慢的动力学行为，且该行为可以被外加等静压所抑制。这是首次观察到在量子临界点附近本征的缓慢动力学行为。4）在另一个同样具有FeO5结构的Z型六角铁氧体Sr3Co2Fe24O41中实现用一阶及二阶磁电耦合系数来进行信息的存储，且可以由电场进行写操作。5）研究了Z型铁氧体磁电耦合效应的微观机理，利用对称性的张量分析方法发现Z型里面电极化可能起源为单自旋的p-d轨道杂化机制。6）研究了Y型六角铁氧体中电场引起的交换偏置效应及太赫兹下电磁振子的激发。7）与物理所龙友文老师合作，研究了线性磁电耦合体系DyCrO4的磁场及掺杂的影响。