双钙钛矿Ba2NaOsO6：磁结构、Kramers双重态与X射线磁二色信号

Simple Realistic Model of Spin Reorientation in 4f-3d Compounds

Spin reorientation is an important phenomenon of rare-earth perovskites, orthoferrites and orthochromites. In this study, we consider a simple but realistic microscopic theory of the spontaneous spin-reorientation transitions induced by the 4f-3d interaction, more specifically, the interaction of the main Kramers doublet or non-Kramers quasi-doublet of the 4f ion with an effective magnetic field induced by the 3d sublattice. The obtained results indicate that the cause of both the temperature and the character of the spin-reorientation transition is a competition between the second and fourth …

在磁场下$5d^2$双钙钛矿中四极有序的出现

Emergence of quadrupolar order under magnetic field in $5d^2$ double perovskites

研究在磁场下三角和面心立方晶格中的相变，发现由场诱导的键依赖交换相互作用导致反铁四极有序与反铁八极有序混合，揭示了五价二价双钙钛矿晶格中的涡旋态。

Competing multipolar orders in a face-centered cubic lattice: Application to the osmium double perovskites

In 5$d^2$ Mott insulators with strong spin-orbit coupling, the lowest pseudospin states form a non-Kramers doublet, which carries quadrupolar and octupolar moments. A family of double perovskites where magnetic ions form a face-centered cubic (fcc) lattice was suggested to unveil an octupolar order offering a rare example in $d$-orbital systems. The proposed order requires a ferromagnetic (FM) octupolar interaction, since the antiferromagnetic (AFM) Ising model is highly frustrated on the fcc lattice. A microscopic model was recently derived for various lattices: for an edge-sharing octahedra …

非中心对称钙钛矿PbVO3和BiCoO3的磁结构

Magnetic structure of noncentrosymmetric perovskites PbVO3 and BiCoO3

众所周知，如果晶体结构没有反转对称性，它可能允许Dzyaloshinskiii-Moriya磁相互作用，在不同的晶体晶胞之间操作，这反过来又会导致长周期自旋螺旋结构的形成。这样的行为是预期的两个简单的钙钛矿PbVO 3和BiCoO 3，在非中心对称的四相P4 mm结构中结晶。然而，我们认为，在现实中，PbVO 3和BiCoO 3的行为应该非常不同。由于奇电子系统的基本Kramers简并性，PbVO 3没有单离子各向异性。因此，PbVO 3的基态将确实是具有大约一百个晶胞的周期的自旋螺旋。然而，偶数电子BiCoO 3具有大的单离子各向异性，这将该系统锁定在共线易轴C型反铁磁基态。我们的理论分析是基于低能模型，来自第一性原理电子结构计算。

铱酸盐以外的Kitaev材料：稀土双钙钛矿中量子无序和Weyl磁振子的有序性

Kitaev materials beyond iridates: order by quantum disorder and Weyl magnons in rare-earth double perovskites

受稀土双钙钛矿实验的启发，我们提出了一个广义的Kitaev-Heisenberg模型来描述稀土矩的Kramers'二重态之间的一般相互作用。我们对这种新模型的平均场相图进行了系统的分析。在相图中，存在具有连续U（1）或O（3）简并度的大区域。由于没有对称性的模型保护这样一个连续的简并，我们预测，量子涨落升降机的连续简并有利于各种磁序的相图。从这个顺序的量子无序机制，我们进一步预测，所产生的有序相的磁激发的特点是几乎无隙的伪戈德斯通模式。我们发现在一定磁序下存在外尔磁振子激发。我们希望我们的预测能启发Kitaev物理的进一步研究，量子无序现象和拓扑自旋波模式在稀土磁体和类似的系统。

面心立方Ba₂(Yb,Nd)NbO₆双钙钛矿中的自旋轨道纠缠阻挫磁性

Spin-orbit-entangled frustrated magnetism in fcc Ba$_2$(Yb,Nd)NbO$_6$ double perovskites

该研究针对面心立方结构的稀土双钙钛矿Ba₂YbNbO₆和Ba₂NdNbO₆，证实其存在自旋轨道耦合诱导的j_eff=1/2基态与中等阻挫的长程磁有序，为稀土自旋轨道纠缠磁体提供了新候选体系。

5d^2双钙钛矿中多极物理的命运

Fate of multipolar physics in $5d^2$ double perovskites

本文通过从头计算研究5d^2锇双钙钛矿的结构稳定性，发现Ba_2CdOsO_6倾向于菱方畸变，并确定了在三角畸变下E_g仍为最低能态的条件，从而揭示非立方环境中多极相仍可涌现。

Antiferromagnetic ordering and dipolar interactions of YbAlO$_3$

In this paper we report low-temperature magnetic properties of the rare-earth perovskite material YbAlO$_3$. Results of elastic and inelastic neutron scattering experiment, magnetization measurements along with the crystalline electrical field (CEF) calculations suggest that the ground state of Yb moments is a strongly anisotropic Kramers doublet, and the moments are confined in the $ab$-plane, pointing at an angle of $φ= \pm 23.5^{\circ}$ to the $a$-axis. With temperature decreasing below $T_{\rm N}=0.88$ K, Yb moments order into the coplanar, but non-collinear antiferromagnetic (AFM) structu…

Multipolar magnetism in d-orbital systems: Crystal field levels, octupolar order, and orbital loop currents

Quantum magnets with spin $J=2$, which arise in spin-orbit coupled Mott insulators, can potentially display multipolar orders. We carry out an exact diagonalization study of a simple octahedral crystal field Hamiltonian for two electrons, incorporating spin-orbit coupling (SOC) and interactions, finding that either explicitly including the $e_g$ orbitals, or going beyond the rotationally invariant Coulomb interaction within the $t_{2g}$ sector, causes a degeneracy breaking of the $J\!=\!2$ level degeneracy. This can lead to a low-lying non-Kramers doublet carrying quadrupolar and octupolar mom…

类Ising反铁磁体DyScO $_3$的磁基态

Magnetic ground state of the Ising-like antiferromagnet DyScO$_3$

我们报告的DyScO $_3$钙钛矿，其特征在于通过单晶和粉末中子散射，并通过磁化测量的低温磁性。低于$T_{\mathrm{N}}=3.15$ K时，Dy $^{3+}$磁矩形成反铁磁结构，其易磁化轴位于$ab$ -平面内.磁矩相对于$b$轴以$\sim\pm{28}^{\circ}$的角度倾斜。结果表明，Dy $^{3+}$的基态Kramers二重态主要由$|\pm 15/2\rangle$本征矢量组成，并在$E_1=24.9$ meV处与第一激发态有很好的分离.这导致极端的伊辛单离子各向异性，$M_{\perp}/M_{\|}\sim{0.05}$。横向磁波动，这是成比例的$M^{2}_{\perp}/M^{2}_{\|}$，被抑制，只允许沿本地伊辛方向的力矩波动。我们还发现，沿结晶$c$轴的Dy-Dy偶极相互作用比面内相互作用大2-4倍。

Ba₂CaOsO₆中铁八极序可能性的X射线磁圆二色光测量评估

Possibility of ferro-octupolar order in Ba$_2$CaOsO$_6$ assessed by X-ray magnetic dichroism measurements

通过X射线吸收光谱和X射线磁圆二色光测量研究Ba₂CaOsO₆中Os⁶+离子的八极序可能性，发现其在约50K以下相变至隐藏序态时存在强交换相互作用。