We present a temperature dependent study of the thermal excitation of magnonic spin currents in two-sublattice magnetic materials. Using atomistic spin model simulations, we study the local magnetization profiles in the vicinity of a temperature step in antiferromagnets, as well as in ferrimagnets. It is shown that the strength of the excitation of the spin currents in these systems scales with the derivative of the magnetization with respect to the temperature.
Weak coupling of pseudoacoustic phonons and magnon dynamics in incommensurate spin ladder compound Sr14Cu24O41
有趣的晶格动力学已被预测为包含无公度子结构的非周期晶体。在这里，我们报告的非弹性中子散射测量的声子和磁振子的色散在Sr 14 Cu 24 O 41，其中包含无公度的一维（1D）链和二维（2D）的梯形子结构。两个不同的赝声学声子模式，对应于一个子晶格对其他的滑动运动，观察沿非公度轴极化的原子运动。在长波长范围内，滑动模的能隙非常小，仅为1.7-1.9 meV，表明两个无公度子晶格之间存在弱相互作用.测量还揭示了阶梯子晶格的带隙和陡峭的线性磁振子色散。该磁振子支的高群速度以及与声学和赝声学声子的弱耦合可以解释Sr 14 Cu 24 O 41晶体中大的磁振子热导率。此外，从测量的总比热和声子态密度确定的磁振子比热，并表现出肖特基异常，由于带隙的自旋链的磁振子模式。这些发现提供了新的见解声子和磁振子动力学和无公度磁性晶体，包含低维子结构的热输运性质。
We theoretically study spin pumping from a layered van der Waals antiferromagnet in its canted ground state into an adjacent normal metal. We find that the resulting dc spin pumping current bears contributions along all spin directions. Our analysis allows for detecting intra- and cross-sublattice spin-mixing conductances via measuring the two in-plane spin current components. We further show that sublattice symmetry-breaking Gilbert damping can be realized via interface engineering and induces a dissipative coupling between the optical and acoustic magnon modes. This realizes magnon level att…
Employing the concept of two-mode squeezed states from quantum optics, we demonstrate a revealing physical picture for the antiferromagnetic ground state and excitations. Superimposed on a N{é}el ordered configuration, a spin-flip restricted to one of the sublattices is called a sublattice-magnon. We show that an antiferromagnetic spin-up magnon is comprised by a quantum superposition of states with $n+1$ spin-up and $n$ spin-down sublattice-magnons, and is thus an enormous excitation despite its unit net spin. Consequently, its large sublattice-spin can amplify its coupling to other excitatio…
The Dzyaloshinskii-Moriya interaction (DMI) is at the heart of many modern developments in the research field of spintronics. DMI is known to generate noncollinear magnetic textures, and can take two forms in antiferromagnets: homogeneous or inter-sublattice, leading to small, canted moments and inhomogeneous or intra-sublattice, leading to formation of chiral structures. In this work, we first determine the strength of the effective field created by the DMI, using SQUID based magnetometry and transport measurements, in thin films of the antiferromagnetic iron oxide hematite, $α$-Fe$_2$O$_3$. …
We investigate theoretically magnon-mediated superconductivity in a heterostructure consisting of a normal metal and a two-sublattice antiferromagnetic insulator. The attractive electron-electron pairing interaction is caused by an interfacial exchange coupling with magnons residing in the antiferromagnet, resulting in p-wave, spin-triplet superconductivity in the normal metal. Our main finding is that one may significantly enhance the superconducting critical temperature by coupling the normal metal to only one of the two antiferromagnetic sublattices employing, for example, an uncompensated …
Recent investigations of the quantum properties of an antiferromagnet in the spin wave approximation have identified the eigenstates as two-mode squeezed sublattice states. The uniform squeezed vacuum and one-magnon states were shown to display a massive sublattice entanglement. Here we expand this investigation and study the squeezing properties of all sublattice Fock states throughout the magnetic Brillouin zone. We derive the full statistics of the sublattice magnon number with wave number $\vec k$ in the ground state and show that magnons are created in pairs with opposite wavevectors, hen…
Spin currents are generated within the bulk of magnetic materials due to heat flow, an effect called intrinsic spin-Seebeck. This bulk bosonic spin current consists of a diffusing thermal magnon cloud, parametrized by the magnon chemical potential ($μ_{m}$), with a diffusion length of several microns in yttrium iron garnet (YIG). Transient opto-thermal measurements of the spin-Seebeck effect (SSE) as a function of temperature reveal the time evolution of $μ_{m}$ due to intrinsic SSE in YIG. The interface SSE develops at times < 2 ns while the intrinsic SSE signal continues to evolve at times >…
Understanding Damping Mechanisms via Spin Diffusion Length in Low-damping Li$_{0.5}$Al$_{1.0}$Fe$_{1.5}$O$_4$ Spinel Ferrite Thin Films
Stanford University（斯坦福大学）；SLAC National Accelerator Laboratory（SLAC国家加速器实验室）；University of California, Irvine（加州大学尔湾分校）；University of California San Diego（加州大学圣地亚哥分校）
Electric-Switchable Chiral Magnons in PT-Symmetric Antiferromagnets
Ministry of Education Key Laboratory for Nonequilibrium Synthesis and Modulation of Condensed Matter, Shaanxi Province Key Laboratory of Advanced Functional Materials and Mesoscopic Physics, School of Physics, Xi’an Jiaotong University（西安交通大学物理学院）；Division of Physics and Applied Physics, School of Physics and Mathematical Sciences, Nanyang Technological University（南洋理工大学物理与数学科学学院）；Department of Physics, University of Science and Technology of China（中国科学技术大学物理系）；Guangdong Basic Research Center of Excellence for Structure and Fundamental Interactions of Matter, Guangdong Provincial Key Laboratory of Quantum Engineering and Quantum Materials, School of Physics, South China Normal University（华南师范大学物理学院）
Using a combination of density functional theory (DFT) and spin-wave theory methods, we investigate the magnetic interactions and spin excitations in semiconducting VI$_3$. Exchange parameters of monolayer, bilayer, and bulk forms are evaluated by mapping the magnetic energies of various spin configurations, calculated using DFT+$U$, onto the Heisenberg model. The intralayer couplings remain largely unchanged in three forms of VI$_3$, while the interlayer couplings show stronger dependence on the dimensionality of the materials. We calculate the spin-wave spectra within a linear spin-wave theo…
Spin transport through magnetic insulators has been demonstrated in a variety of materials and is an emerging pathway for next-generation spin-based computing. To modulate spin transport in these systems, one typically applies a sufficiently strong magnetic field to allow for deterministic control of magnetic order. Here, we make use of the well-known multiferroic magnetoelectric, BiFeO3, to demonstrate non-volatile, hysteretic, electric-field control of thermally excited magnon current in the absence of an applied magnetic field. These findings are an important step toward magnon-based device…
Emergent Skyrmion Hall Effect in $d$-wave Altermagnets at Finite Temperature
School of Physics Science and Information Technology, Liaocheng University（聊城大学物理科学与信息工程学院）；School of Physics and State Key Laboratory of Electronic Thin Films and Integrated Devices, University of Electronic Science and Technology of China（电子科技大学物理学院电子薄膜与集成器件国家重点实验室）；Guangdong Provincial Key Laboratory of Quantum Engineering and Quantum Materials and Institute for Advanced Materials, South China Academy of Advanced Optoelectronics, South China Normal University（华南师范大学广东省量子工程与量子材料重点实验室先进材料研究院南方先进光电子研究院）
Understanding spin control mechanisms is an important part of condensed matter physics and the theoretical basis for designing spintronic devices. In this letter, based on four-sublattices molecular field theory, we propose that the underlying NdFe1-xCrxO3 magnetic mechanism is driven by spin reorientation sensitive to temperature. The actual coupling angular momentum, angle between the Nd3+ and Cr3+/Fe3+ moments at the given temperature is realized via the Nd3+ magnetic moment projection onto the Cr3+/Fe3+ plane. As the temperature increases, the angle between the moment of Nd3+ and the momen…
We demonstrate optical control of magnons using femtosecond laser pulses by performing ab-initio real-time time-dependent density functional theory (TDDFT) simulations. We predict that the spin-wave dynamics in Fe$_{50}$Ni$_{50}$ can be manipulated by tailoring the applied laser pulse via three distinct mechanisms: (1) element selective destruction of magnon modes depending on the laser intensity, (2) delay dependent freezing of the magnon mode into a transient non-collinear state (where delay is in the pulse peak with respect to the start of simulations), and (3) optically induced inter subla…
Currently, thermally excited magnons are being intensively investigated owing to their potential in computing devices and thermoelectric conversion technologies. We report the detection of thermal magnon current propagating in a magnetic insulator yttrium iron garnet under a temperature gradient using a quantum sensor: electron spins associated with nitrogen-vacancy (NV) centers in diamond. Thermal magnon current was observed as modified Rabi oscillation frequencies of NV spins hosted in a beam-shaped bulk diamond that resonantly coupled with coherent magnon propagating over a long distance. A…
In an easy-plane antiferromagnet with the Dzyaloshinskii-Moriya interaction (DMI), magnons are subject to an effective spin-momentum locking. An in-plane temperature gradient can generate interfacial accumulation of magnons with a specified polarization, realizing the magnon thermal Edelstein effect. We theoretically investigate the injection and detection of this thermally-driven spin polarization in an adjacent heavy metal with strong spin Hall effect. We find that the inverse spin Hall voltage depends monotonically on both temperature and the DMI but non-monotonically on the hard-axis aniso…
Compensation-Like Temperature and Spin-Flip Switch in Strained Thulium Iron Garnet Thin Films: Tuning Sublattice Interactions for Ferrimagnetic Spintronics
Low power spintronic devices based on the propagation of pure magnonic spin currents in antiferromagnetic insulator materials offer several distinct advantages over ferromagnetic components including higher frequency magnons and a stability against disturbing external magnetic fields. In this work, we make use of the insulating antiferromagnetic phase of iron oxide, the mineral hematite $α$-Fe$_2$O$_3$ to investigate the long distance transport of thermally generated magnonic spin currents. We report on the excitation of magnons generated by the spin Seebeck effect, transported both parallel a…
We explore spin dynamics in Cu(1,3-bdc), a quasi-2D topological magnon insulator. The results show that the thermal evolution of Landé $g$-factor ($g$) is anisotropic: $g_\textrm{in-plane}$ reduces while $g_\textrm{out-plane}$ increases with increasing temperature $T$. Moreover, the anisotropy of the $g$-factor ($Δg$) and the anisotropy of saturation magnetization ($ΔM_\textrm{s}$) are correlated below 4 K, but they diverge above 4 K. We show that the electronic orbital moment contributes to the $g$ anisotropy at lower $T$, while the topological orbital moment induced by thermally excited spin…
We investigate the effect of magnon-magnon interactions on the dispersion and polarization of magnons in collinear antiferromagnetic (AF) insulators at finite temperatures. In two-sublattice AF systems with either uniaxial or biaxial magnetocrystalline anisotropies, we implement a self-consistent Hartree-Fock mean-field approximation to explore the nonlinear thermal interactions. The resulting nonlinear magnon interactions separate into two-magnon intra- and interband scattering processes. Furthermore, we compute the temperature dependence of the magnon bandgap and AF resonance modes due to no…
We investigate magnon spin transport in epitaxial nickel ferrite (NiFe$_2$O$_4$, NFO) films grown on magnesium gallate spinel (MgGa$_2$O$_4$, MGO) substrates, which have a lattice mismatch with NFO as small as 0.78%, resulting in the reduction of antiphase boundary defects and thus in improved magnetic properties in the NFO films. In the nonlocal transport experiments, enhanced signals are observed for both electrically and thermally excited magnons, and the magnon relaxation length ($λ_m$) of NFO is found to be around 2.5 $μ$m at room temperature. Moreover, at both room and low temperatures, …
In an antiferromagnet (AF) with uniaxial anisotropy, spin-up and spin-down magnons coexist and form an intrinsic degree of freedom resembling electrons. When polarized by an adjacent ferromagnet (F), a magnonic pure spin current can be thermally generated in an AF. We explore thermal magnon transport in an insulating F/AF/F trilayer where propagating magnons inside the AF spacer can transfer angular momenta between the two Fs. We find that a sufficiently large temperature gradient can switch the downstream F via magnonic spin-transfer torque if it is initially antiparallel with the upstream F.…
Plaid-Like Spin Splitting and Chirality of Magnon Bands in Antiferromagnetic MnTe$_2$
Sejong University（世宗大学）；Korea Advanced Institute of Science and Technology (KAIST)（韩国科学技术院）；Sungkyunkwan University（成均馆大学）；Institute of Physics, Academia Sinica（中央研究院物理研究所）
Due to the small photon momentum, optical spectroscopy commonly probes magnetic excitations only at the center of the Brillouin zone; however, there are ways to override this restriction. In the case of the distorted kagome quantum magnet Y-kapellasite, Y$_3$Cu$_9$(OH)$_{19}$Cl$_8$, under scrutiny here, the magnon density of states can be accessed over the entire Brillouin zone through three-center magnon excitations. This mechanism is aided by the three different magnetic sublattices and strong short-range correlations in the distorted kagome lattice. The results of THz time-domain experiment…
