We investigate the ac transport of magnetization in non-itinerant quantum systems such as spin chains described by the XXZ Hamiltonian. Using linear response theory, we calculate the ac magnetization current and the power absorption of such magnetic systems. Remarkably, the difference in the exchange interaction of the spin chain itself and the bulk magnets (i.e. the magnetization reservoirs), to which the spin chain is coupled, strongly influences the absorbed power of the system. This feature can be used in future spintronic devices to control power dissipation. Our analysis allows to make quantitative predictions about the power absorption and we show that magnetic systems are superior to their electronic counter parts.
Local spin magnetization in itinerant non-collinear magnets: The local spin Berry curvature
National Institute for R&D of Isotopic and Molecular Technologies（同位素与分子技术国家研发研究所）；Laboratoire de Physique des Solides, Université Paris-Saclay, CNRS（巴黎萨克雷大学CNRS固体物理实验室）
We have performed single-atom magnetization curve (SAMC) measurements and inelastic scanning tunneling spectroscopy (ISTS) on individual Fe atoms on a Cu(111) surface. The SAMCs show a broad distribution of magnetic moments with $\unit[3.5]{μ_{\rm B}}$ being the mean value. ISTS reveals a magnetization excitation with a lifetime of $\unit[200]{fsec}$ which decreases by a factor of two upon application of a magnetic field of $\unit[12]{T}$. The experimental observations are quantitatively explained by the decay of the magnetization excitation into Stoner modes of the itinerant electron system a…
Staggered orbital magnetization from itinerant electrons: orbital antiferro- and ferrimagnetic phases
Instituto de Física, Universidade Federal Fluminense（弗鲁米嫩塞联邦大学物理研究所）；International Iberian Nanotechnology Laboratory (INL)（伊比利亚纳米技术国际实验室）；Centro Brasileiro de Pesquisas Físicas (CBPF)（巴西物理研究中心）；Physics Center of Minho and Porto Universities (CF-UM-UP)（米尼奥与波尔图大学物理中心）
We present a microscopic calculation of magnetization damping for a magnetic "toy model." The magnetic system consists of itinerant carriers coupled antiferromagnetically to a dispersionless band of localized spins, and the magnetization damping is due to coupling of the itinerant carriers to a phonon bath in the presence of spin-orbit coupling. Using a mean-field approximation for the kinetic exchange model and assuming the spin-orbit coupling to be of the Rashba form, we derive Boltzmann scattering integrals for the distributions and spin coherences in the case of an antiferromagnetic exchan…
We study magnetization reversal of nanostructures of the itinerant ferromagnet SrRuO3 (Tc~150 K). We find that down to 10 K the magnetization reversal is dominated by thermal activation. From 2 - 10 K, the magnetization reversal becomes independent of temperature, raising the possibility for reversal dominated by macroscopic quantum tunneling (MQT). A 10 K crossover to MQT is consistent with the extremely large anisotropy field (~7 T) of SrRuO3.
Magnetization reversal is a well-studied problem with obvious applicability in computer hard-drives. One can accomplish a magnetization reversal in at least one of two ways: application of a magnetic field, or through a spin current. The latter is more amenable to a fully quantum mechanical analysis. We formulate and solve the problem whereby a spin current interacts with a ferromagnetic Heisenberg spin chain, to eventually reverse the magnetization of the chain. Spin-flips are accomplished through both elastic and inelastic scattering. A consequence of the inelastic scattering channel, when i…
We develop a theory of spin noise spectroscopy of itinerant, noninteracting, spin-carrying fermions in different regimes of temperature and disorder. We use kinetic equations for the density matrix in spin variables. We find a general result with a clear physical interpretation, and discuss its dependence on temperature, the size of the system, and applied magnetic field. We consider two classes of experimental probes: 1. electron-spin-resonance (ESR)-type measurements, in which the probe response to a uniform magnetization increases linearly with the volume sampled, and 2. optical Kerr/Farada…
Non reciprocal spin waves have a chiral asymmetry so that their energy is different for two opposite wave vectors. They are found in atomically thin ferromagnetic overlayers with in plane magnetization and are linked to the anti-symmetric Dzyaloshinskii-Moriya surface exchange. We use an itinerant fermion theory based on first principles calculations to predict that non-reciprocal magnons can occur in Fe$_3$GeTe$_2$, the first stand alone metallic two dimensional crystal with off-plane magnetization. We find that both the energy and lifetime of magnons are non-reciprocal and we predict that ac…
We study the anomalous Hall effect and orbital magnetization in chiral antiferromagnets, constructing a simple tight-binding model on a stacked Kagome lattice structure with spin-orbit coupling and the exchange interaction between the localized spins and itinerant electrons. It is shown that the ground state is an orbital ferromagnet with the easy-plane anisotropy. The relation between the orbital magnetization and the configuration of the Weyl points are discussed.
As an alternative to conventional magnetic field, the effective spin-orbit field in transition metals, derived from the Rashba field experienced by itinerant electrons confined in a spatial inversion asymmetric plane through the s-d exchange interaction, is proposed for the manipulation of magnetization. Magnetization switching in ferromagnetic thin films with perpendicular magnetocrystalline anisotropy can be achieved by current induced spin-orbit field, with small in-plane applied magnetic field. Spin-orbit field induced by current pulses as short as 10 ps can initiate ultrafast magnetizatio…
We study spin relaxation in dilute magnetic semiconductors near a ferromagnetic transition, where spin fluctuations become strong. An enhancement in the scattering rate of itinerant carriers from the spin fluctuations of localized impurities leads to a change in the dominant spin relaxation mechanism from Dyakonov-Perel to spin flips in scattering. On the ferromagnetic side of the transition, we show that due to the presence of two magnetic components -- the itinerant carriers and the magnetic impurities -- with different gyromagnetic ratios, the relaxation rate of the total magnetization can …
A consistent theory to describe the correlated dynamics of quantum mechanical itinerant spins and semiclassical local magnetization is given. We consider the itinerant spins as quantum mechanical operators, whereas local moments are considered within classical Lagrangian formalism. By appropriately treating fluctuation space spanned by basis functions, including a zero-mode wave function, we construct coupled equations of motion for the collective coordinate of the center-of-mass motion and the localized zero-mode coordinate perpendicular to the domain wall plane. By solving them, we demonstra…
Nanomechanical Detection of Itinerant Electron Spin Flip
自旋是一种固有的量子性质，其特征在于角动量。自旋状态的变化相当于角动量或机械扭矩的变化。这种自旋感应力矩在从测量光子的角动量、金属的g因子和磁共振到磁性多层膜中的磁化反转的实验中被称为内在机制。引入到纳米线中的自旋极化电流产生与巡游电子自旋翻转相关的力矩。在这里，我们报告的直接测量这种机械扭矩和巡回电子自旋极化在一个集成的纳米扭转振荡器，这可能会产生新的信息巡回的d-带电子。10^{-22} N m/ \sqrt{Hz}的前所未有的扭矩灵敏度可以使自旋电子学、CP破坏力的精确测量、DNA的解扭和扭矩产生分子的应用成为可能。
Magnetization relaxation in (Ga,Mn)As ferromagnetic semiconductors
本文描述了铁磁半导体（Ga，Mn）As合金中由于p-d动力学交换耦合与巡游自旋子系统的Mn局域磁矩磁化弛豫的理论。理论上的吉尔伯特阻尼系数暗示了这种机制作为一个函数的Mn矩密度，空穴浓度，和准粒子寿命计算。与实验铁磁共振数据的比较表明，在退火强金属样品，p-d耦合有助于显着的阻尼率的磁化进动在低温下。通过结合理论吉尔伯特系数的值的磁各向异性能量，我们估计，在全半导体三层器件的自旋转移磁化翻转的典型的临界电流可以低至$\sim 10^{5} {\rm A cm}^{-2}$。
We develop a comprehensive theory for magnetoelectricity in magnetically ordered quasi-2D systems whereby in thermal equilibrium an electric field can induce a magnetization $m$ and a magnetic field can induce a polarization. This effect requires that both space-inversion and time-reversal symmetry are broken. Antiferromagnetic (AFM) order plays a central role in this theory. We define a Néel operator $τ$ such that a nonzero expectation value $\langle τ\rangle$ signals AFM order, in the same way $m$ signals ferromagnetic (FM) order. While $m$ is even under space inversion and odd under time re…
We theoretically investigate laser-induced spin transport in metallic magnetic heterostructures using an effective spin transport description that treats itinerant electrons and thermal magnons on an equal footing. Electron-magnon scattering is included and taken as the driving force for ultrafast demagnetization. We assume that in the low-fluence limit the magnon system remains in a quasi-equilibrium, allowing a transient nonzero magnon chemical potential. In combination with the diffusive transport equations for the itinerant electrons, the description is used to chart the full spin dynamics…
Recent experimental realization of strongly imbalanced mixtures of ultracold atoms opens new possibilities for studying impurity dynamics in a controlled setting. We discuss how the techniques of atomic physics can be used to explore new regimes and manifestations of Anderson's orthogonality catastrophe (OC), which could not be accessed in solid state systems. We consider a system of impurity atoms localized by a strong optical lattice potential and immersed in a sea of itinerant Fermi atoms. Ramsey interference experiments with impurity atoms probe OC in the time domain, while radio-frequency…
Spin pumping is the emission of a spin current by a magnetization dynamics while spin transfer stands for the excitation of magnetization by spin currents. Using Onsager's reciprocity relations we prove that spin pumping and spin-transfer torques are two fundamentally equivalent dynamic processes in magnetic structures with itinerant electrons. We review the theory of the coupled motion of the magnetization order parameter and electron for textured bulk ferromagnets (e.g. containing domain walls) and heterostructures (such as spin valves). We present first-principles calculations for the mater…
