This work develops a new generalized technique for determining the static and dynamic properties of any non-collinear magnetic system. By rotating the spin operators into the local spin reference frame, we evaluate the zeroth, first, and second order terms in a Holstein-Primakoff expansion, and through a Green's functions approach, we determine the structure factor intensities for the spin-wave frequencies. To demonstrate this technique, we examine the spin-wave dynamics of the generalized Villain model with a varying interchain interaction. The new interchain coupling expands the overall phase diagram with the realization of two non-equivalent canted spin configurations. The rotational Holstein-Primakoff expansion provides both analytical and numerical results for the spin dynamics and intensities of these phases.
Large magneto-optical Kerr effect induced by collinear antiferromagnetic order
University of Tokyo（东京大学）；RIKEN Center for Emergent Matter Science (CEMS)（理化学研究所 新兴物质科学中心）；Hokkaido University（北海道大学）；Tokyo Metropolitan University（东京都立大学）；PRESTO, Japan Science and Technology Agency (JST)（日本科学技术振兴机构 PRESTO）；Research Center for Advanced Science and Technology (RCAST), University of Tokyo（东京大学 先进科学技术研究中心）；Institute for Solid State Physics, University of Tokyo（东京大学 固体物理研究所）；Department of Physics, University of Tokyo（东京大学 物理学系）；Institute of Engineering Innovation, University of Tokyo（东京大学 工学创新研究所）
We extend the density functional perturbation theory formalism to the case of non-collinear magnetism. The main problem comes with the exchange-correlation (XC) potential derivatives, which are the only ones that are affected by the non-collinearity of the system. Most of the present XC functionals are constructed at the collinear level, such that the off-diagonal (containing magnetization densities along $x$ and $y$ directions) derivatives cannot be calculated simply in the non-collinear framework. To solve this problem, we consider here possibilities to transform the non-collinear XC derivat…
The $4d$ and $5d$ transition metal oxides have become important members of the emerging quantum materials family due to competition between onsite Coulomb repulsion ($U$) and spin-orbit coupling (SOC). Specifically, the systems with $d^5$ electronic configuration in an octahedral environment are found to be capable of posessing invariant semimetallic state and perturbations can lead to diverse magnetic phases. In this work, by formulating a multi-band Hubbard model and performing SOC tunable DFT+$U$ calculations on a prototype SrIrO$_3$ and extending the analysis to other iso-structural and is…
The ground-state magnetic structures of the Eu$^{2+}$ spins in recently discovered RbEu(Fe$_{1-x}$Ni$_{x}$)$_{4}$As$_{4}$ superconductors have been investigated by neutron powder diffraction measurements. It is found that as the superconductivity gets suppressed with the increase of Ni doping, the magnetic propagation vector of the Eu sublattice diminishes, corresponding to the decrease of the rotation angle between the moments in neighboring Eu layers. The ferromagnetic Eu layers are helically modulated along the $\mathit{c}$ axis with an incommensurate magnetic propagation vector in both the…
Recent studies revealed that the electric multipole moments of insulators result in fractional electric charges localized to the hinges and corners of the sample. We here explore the magnetic analog of this relation. We show that a collinear antiferromagnet with spin $S$ defined on a $d$-dimensional cubic lattice features fractionally quantized magnetization $M_{\text{c}}^z=S/2^d$ at the corners. We find that the quantization is robust even in the presence of gapless excitations originating from the spontaneous formation of the Néel order, although the localization length diverges, suggesting …
Sr$_{3}$ZnIrO$_{6}$ is an effective spin one-half Mott insulating iridate belonging to a family of magnets which includes a number of quasi-one dimensional systems as well as materials exhibiting three dimensional order. Here we present the results of an extensive investigation into the magnetism including heat capacity, a.c. susceptibility, muon spin rotation ($μ$SR), neutron diffraction and inelastic neutron scattering on the same sample. It is established that the material exhibits a transition at about $17$ K into a three-dimensional antiferromagnetic structure with propagation vector $\bo…
Magnetism and electronic dynamics in $CuCr_{2-x}Sn_xS_4$ spinels studied by transferred hyperfine fields at $^{119}Sn$ and muon spin rotation and relaxation
Quantum effects fundamentally engender exotic physical phenomena in macroscopic systems, which advance next-generation technological applications. Rotational tunneling that represents the quantum phenomenon of the librational motion of molecules is ubiquitous in hydrogen-contained materials. However, its direct manifestation in realizing macroscopic physical properties is elusive. Here we report an observation of reentrant ferroelectricity under low pressure that is mediated by the rotational tunneling of ammonium ions in molecule-based (NH$_4$)$_2$FeCl$_5 \cdot$H$_2$O. Applying a small pressu…
The magnetic order induced by the pressure was studied in single crystalline FeSe by means of muon-spin rotation ($μ$SR) technique. By following the evolution of the oscillatory part of the $μ$SR signal as a function of angle between the initial muon-spin polarization and 101 axis of studied crystal it was found that the pressure induced magnetic order in FeSe corresponds either to the collinear (single-stripe) antiferromagnetic order as observed in parent compounds of various FeAs-based superconductors or to the Bi-Collinear order as obtained in FeTe system, but with the Fe spins turned by 45…
Université Grenoble Alpes, CNRS, Grenoble INP, Institut Néel（格勒诺布尔阿尔卑斯大学、法国国家科学研究中心、格勒诺布尔理工学院、内尔研究所）；Technische Universität München（慕尼黑工业大学）；Munich Center for Quantum Science and Technology (MCQST)（慕尼黑量子科学与技术中心）；Imperial College London（帝国理工学院）
Exchange interaction tends to favor collinear or coplanar magnetic orders in rotationally invariant spin systems. Indeed, such magnetic structures are usually selected by thermal or quantum fluctuations in highly frustrated magnets. Here we show that a complex noncoplanar magnetic order with a quadrupled unit cell is stabilized by itinerant electrons on the pyrochlore lattice. Specifically we consider the Kondo-lattice and Hubbard models at quarter filling. The electron Fermi 'surface' at this filling factor is topologically equivalent to three intersecting Fermi circles. Perfect nesting of th…
We report the $\mathbf{H}-T$ phase diagram of $S=1/2$ strongly frustrated anisotropic spin chain material linarite PbCuSO$_4$(OH)$_2$ in tilted magnetic fields up to 10 T and temperatures down to 0.2 K. By means of torque magnetometry we investigate the phase diagram evolution as the magnetic field undergoes rotation in $\mathbf{ba}^{\ast}$ and $\mathbf{bc}$ planes. The key finding is the robustness of the high field spin density wave-like phase, which may persist even as the external field goes orthogonal to the chain direction $\mathbf{b}$. In contrast, the intermediate collinear antiferroma…
The standard spin-transfer torque (STT)---where spin-polarized current drives dynamics of magnetization viewed as a classical vector---requires noncollinearity between electron spins carried by the current and magnetization of a ferromagnetic layer. However, recent experiments [A. Zholud et al., Phys. Rev. Lett. 119, 257201 (2017)] observing magnetization dynamics in spin valves at cryogenic temperatures, even when electron spin is collinear to magnetization, point at overlooked quantum effects in STT which can lead to highly nonclassical magnetization states. Using fully quantum many-body tre…
Orbital altermagnetism on the kagome lattice and possible application to $A$V$_3$Sb$_5$
The Grainger College of Engineering, University of Illinois Urbana-Champaign（伊利诺伊大学厄巴纳-香槟分校格雷恩格工程学院）；Anthony J. Leggett Institute for Condensed Matter Theory, The Grainger College of Engineering, University of Illinois Urbana-Champaign（伊利诺伊大学厄巴纳-香槟分校格雷恩格工程学院安东尼·J·利盖特凝聚态理论研究所）；Department of Chemical Engineering and Materials Science, University of Minnesota（明尼苏达大学化学工程与材料科学系）
The bilayer iridate Sr$_3$Ir$_2$O$_7$ is a $c$-axis collinear antiferromagnet, held there by a giant interlayer pseudodipolar anisotropy, whereas single-layer Sr$_2$IrO$_4$ cants in the $ab$ plane. We show from first principles that biaxial compression of a few percent ($\varepsilon_c\approx-2.4\%$) flops the easy axis of Sr$_3$Ir$_2$O$_7$ into the plane. A magnetic model Hamiltonian built from Wannier functions with no fitted parameter---reproducing the giant magnon gap of the bulk, so far known only from fits to experiment---identifies the mechanism. Compression collapses the interlayer exch…
We present results of first-principles calculations of the magnetic properties of Fe chains deposited on the Re(0001) surface. By increasing the length of the chain, a transition is found from an almost collinear antiferromagnetic state for a 5-atom-long chain to a spin spiral state with the rotational plane slightly tilted from the surface of the substrate for the 15-atom-long chain. It is shown that a classical spin model derived from the ab initio calculations containing only two-spin interactions supports opposite chirality of the spin spiral compared to a direct optimization of the spin c…
Effects of Crystal Structure and the On-Site Coulomb Interactions on the Electronic and Magnetic Structure of Pyrochlores $A_2$Mo$_2$O$_7$ (A= Y, Gd, and Nd)
受最近实验研究的启发，我们研究了钼高温超导体$A_2$ Mo $_2$ O $_7$（$A$ = Y，Nd，Gd）的磁结构及其对电子性质的影响.后者与12个Mo（$t_{2g}$）带的行为密切相关，这些带位于费米能级附近，并且与光谱的其余部分很好地分离。我们使用平均场Hartree-Fock方法，它结合了这些带的电子结构的精细细节，从局域密度近似，自旋轨道相互作用和Mo（4d）电子之间的原位库仑相互作用的传统计算中提取，以最一般的旋转不变形式处理。库仑排斥U在这个问题中起着非常重要的作用，半经验值U $\sim$ 1.5-2.5 eV同时解释了金属-绝缘体（M-I）相变、铁磁（FM）-自旋玻璃（SG）相变以及反常霍尔效应（AHE）的增强. M-I转变主要由$U$控制。由于双交换机制，金属侧的磁结构几乎是共线FM。进入绝缘状态的转变伴随着自旋和轨道磁矩的大倾斜。在绝缘状态下的交换相互作用的符号由Mo-Mo距离控制。较小的距离有利于反铁磁耦合，这预示着SG行为的挫折烧绿石晶格。大的AHE预计在近共线FM状态，M-I转变点附近，并与未淬灭的轨道磁化在Mo网站。我们还预测了在相同的FM化合物大的磁光效应。
We calculate Heisenberg-type magnetic exchange interactions for SrMnO$_3$ under isotropic volume expansion using an approach that is based on total energy variations due to infinitesimal spin rotations around a given reference state. Our total energy calculations using density functional theory (DFT) indicate a transition from antiferromagnetic to ferromagnetic coupling for increasing interatomic distances, corresponding to a sign change of the nearest neighbor exchange interaction. This sign change cannot easily be understood from a standard superexchange mechanism. Furthermore, the exchange …
