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多铁性材料因铁电序和磁序之间的交叉耦合机制所衍生的新奇量子效应(如磁电耦合、拓扑电畴等)而备受关注. 然而, 受限于铁电性源于d0电子构型而铁磁性依赖于dn电子填充的微观机制互斥性, 具有磁电耦合特性的本征多铁性材料仍然有限. 本研究基于第一性原理密度泛函理论计算, 提出通过构建Aurivillius型界面层来调控PbTiO3钙钛矿的电子结构, 成功诱导出界面局域磁矩. 计算结果表明, 该界面层在保持强电极化(高达116.88 μC/cm2)的同时, 通过界面极化电荷调制界面处氧原子的电子占据态从而诱导出界面磁性, 实现了PbTiO3的磁性与极性之间的耦合. 值得注意的是, 这种磁电耦合的多铁态呈现出显著的界面局域特征, 随着层数的增加, 局域磁矩迅速衰减. 我们的研究提出了一种设计多铁性层并分析了可通过改变极化方向调控磁矩的新机制, 为实现具有磁电耦合的多铁性材料器件提供了新范式.Multiferroic materials have attracted considerable attention due to their novel quantum phenomena, including magnetoelectric coupling and topological domains, which are derived from the cross-coupling mechanism between ferroelectric order and magnetic order. However, the discovery of intrinsic multiferroic materials exhibiting magnetoelectric coupling remains limited, as ferroelectricity typically originates from the d0 electronic configuration, while ferromagnetism relies on partially filled dn state. Based on first principles calculations, this work demonstrates that electronic structure of PbTiO3 perovskite can be engineered by introducing an Aurivillius-type interface layer, which induces localized magnetic moments at the interface. The results reveal that when the system maintains strong electric polarization (up to 116.88 μC/cm2), the interfacial charge changes the electron occupancy of oxygen atoms, thereby resulting in interface magnetism and magnetoelectric coupling in PbTiO3. Notably, this multiferroic state exhibits pronounced interface localization, with the magnetic moment decaying rapidly as the layer thickness increases. Importantly, the emergent magnetism is asymmetric, resulting in a net positive spontaneous magnetization of 2.0μB. This observation indicates the emergence of ferrimagnetism at the interface. Furthermore, the interfacial region displays p-type conductivity behavior, exhibiting characteristics of two-dimensional hole gas (2DHG), and the density of holes and the density of charge carriers at the interface are several times higher than those in typical heterostructures. Overall, our work proposes a novel mechanism for designing multiferroic and providing a promising strategy for developing magnetoelectric-coupled multiferroic devices.
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Keywords:
- first-principles calculation /
- multiferroic /
- interfaces /
- PbTiO3
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图 1 模拟模型 (a) 块体单胞PbTiO3的原子结构; (b) PbTiO3 Aurivillious型界面的构造示意图; (c) 上层和下层的剖面图; (d) PbTiO3中Aurivillious型界面的仿真模型, 其中n = 6
Fig. 1. Simulation model: (a) Atomic structure of bulk unit cell PbTiO3; (b) schematic illustration of the schematic diagram of PbTiO3 Aurivillious interface; (c) cross-section view of upper part and cross-section view of lower part; (d) simulation model of Aurivillious type interface in PbTiO3 with n = 6.
图 2 四方PbTiO3的相图. 由A, B, C和D组成的四边形区域显示了PbTiO3的稳定范围
Fig. 2. Phase diagram of tetragonal PbTiO3. The quadrilateral area composed of A, B, C, and D shows the stability range of PbTiO3.
图 3 界面的铁电性 (a) PbO层中沿z轴的归一化Pb—O相对位移; (b) TiO2层中沿z轴的归一化Ti—O相对位移; (c) 每层的局域极化
Fig. 3. Ferroelectrixity of interface: (a) Normalized Pb—O relative displacements in the PbO layers along the z axis; (b) normalized Ti—O relative displacements in the TiO2 layers along the z axis; (c) the local polarization in each layer.
图 4 界面的磁性 (a) 沿[001]方向初始磁性配置的PbTiO3中Aurivillius型界面周围的磁自旋密度分布, 其中紫色区域和黄色区域分别表示自旋密度为+0.005μB·Å–1和–0.005μB·Å–1的等值面; (b) 界面周围各原子层中O原子的磁矩
Fig. 4. Magnetic properties of interface: (a) Magnetic spin-density distribution around Aurivillious type interface in PbTiO3 for initial polarization configuration along the [001] direction, in which the purple area and yellow area represent the iso-surfaces of spin-densities of +0.005μB·Å–1 and –0.005μB·Å–1, respectively; (b) the magnetic moment of O atoms in each atomic layer around the interface.
图 5 (a) PbTiO3中Aurivillius型的总态密度(DOS), 红色和蓝色线分别表示自旋朝上和自旋朝下的占据(未占据)态; (b) Aurivillius型界面中的电荷密度分布, 绿色区域表示电荷密度为0.01 Å–3的等值面. 层分辨的部分态密度, 红色和黑线分别表示O的2p轨道自旋朝上和O的2p轨道自旋朝下的占据(未占据)态, 蓝色和绿线分别表示Pb的6s轨道自旋朝上和Pb的6s轨道自旋朝下的占据(未占据)态
Fig. 5. (a) Total DOS for the Aurivillious-type interface in PbTiO3, the red and blue lines indicate the occupied (unoccupied) states of up-spin and down-spin, respectively; (b) charge density distribution in Aurivillius-type interface, the green area represents the iso-surface of charge densities of 0.01 Å–3. The layer resolved partial DOS, the red and black line indicate the occupied (unoccupied) states of O 2p up-spin and O 2p down-spin, respectively, the blue and green line indicate the occupied (unoccupied) states of Pb 6s up-spin and Pb 6s down-spin, respectively.
图 6 Aurivillius型界面中不同初始极化配置下的磁自旋密度分布, 沿 (a) [00$ \bar{1} $]方向和 (b) [100]方向, 其中紫色区域和黄色区域分别表示自旋密度为+0.005μB·Å–1和–0.005μB·Å–1的等值面; (c) 沿[001]方向、[00$ \bar{1} $]方向和[100]方向的不同初始极化配置下每层的dPiz/dz值
Fig. 6. Magnetic spin-density distribution in Aurivillius-type interface with the different initial polarization configuration along (a) the [00$ \bar{1} $] direction and (b) the [100] direction, in which the purple area and yellow area represent the iso-surfaces of spin-densities of +0.005μB·Å–1 and –0.005μB·Å–1, respectively; (c) the magnitude of dPiz/dz in each layer of the different initial polarization configuration along the [001] direction, the[00$ \bar{1} $] direction, and the [100] direction, respectively.
图 A1 (a) Pb中心晶格; (b) Ti中心晶格; (c) PbO平面中的O中心晶格; (d) TiO2平面中的O中心晶格
Fig. A1. (a) Pb-centered lattice; (b) Ti-centered lattice; (c) O-centered lattice in the PbO plane; (d) O-centered lattice in the TiO2 plane.
表 1 点A, B, C和D处的化学势数值
Table 1. The values of chemical potential for points A, B, C, and D, respectively.
chemical potential/eV ΔμPb ΔμTi ΔμO μPb μTi μO A 0 –5.73 –2.28 –4.56 –17.69 –9.42 B 0 –4.93 –2.54 –4.56 –16.90 –9.69 C –2.28 –10.28 0 –6.84 –22.25 –7.14 D –2.54 –10.02 0 –7.11 –21.98 –7.14 
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