All-optical re-switching has been investigated in the half-metallic Heusler ferrimagnet Mn2Ru0.9Ga, where Mn atoms occupy two inequivalent sites in the XA-type structure. The effect of a second 200 fs 800 nm pump pulse that follows a first pulse, when both are above the threshold for switching, is studied as a function of t12, the time between them. The aims are to identify the physical mechanisms involved and to determine the minimum time needed for re-switching. The time trajectory of the switching process on a plot of sublattice angular momentum, S4a vs S4c, is in three stages; When t < 0.1 ps, the sublattice moments are rapidly disordered, but not destroyed, while conserving net angular momentum via optical spin-wave excitations. This leads to transient parallel alignment of the residual Mn spins in the first quadrant. The net angular momentum associated with the majority sublattice then flips in about 2 ps, and a fully-reversed ferrimagnetic state is then established via the spin-lattice interaction, which allows re-switching provided t12 > 10 ps.
Single-pulse switching has been experimentally demonstrated in ferrimagnetic GdFeCo and Mn$_2$Ru$_x$Ga alloys. Complete understanding of single-pulse switching is missing due to the lack of an established theory accurately describing the transition to the non-equilibrium reversal path induced by femtosecond laser photo-excitation. In this work we present general macroscopic theory for the magnetization dynamics of ferrimagnetic materials upon femtosecond laser excitation. Our theory reproduces quantitatively all stages of the switching process observed in experiments. We directly compare our t…
We bridge an essential knowledge gap on the understanding of all-optical ultrafast switching in ferrimagnets; namely, the connection between atomistic spin dynamics methods and macroscopic phenomenological models. All-optical switching of the magnetization occurs after the application of a single femtosecond laser pulse to specific ferrimagnetic compounds. This strong excitation puts the involved degrees of freedom, electrons, lattice and spins out-of-equilibrium between each other. Atomistic spin models have quantitatively described all-optical switching in a wide range of experimental condit…
Interest in all-optical spin switching (AOS) is growing rapidly. The recent discovery of AOS in Mn$_2$RuGa provides a much needed clean case of crystalline ferrimagnets for theoretical simulations. Here, we attempt to simulate it using the state-of-the-art first-principles method combined with the Heisenberg exchange model. We first compute the spin moments at two inequivalent manganese sites and then feed them into our model Hamiltonian. We employ an ultrafast laser pulse to switch the spins. We find that there is a similar optimal laser field amplitude to switch spins. However, we find that …
Ferrimagnetic insulators (FiMI) have been intensively used in microwave and magneto-optical devices as well as spin caloritronics, where their magnetization direction plays a fundamental role on the device performance. The magnetization is generally switched by applying external magnetic fields. Here we investigate current-induced spin-orbit torque (SOT) switching of the magnetization in Y3Fe5O12 (YIG)/Pt bilayers with in-plane magnetic anisotropy, where the switching is detected by spin Hall magnetoresistance. Reversible switching is found at room temperature for a threshold current density o…
Single femtosecond pulse toggle switching of ferrimagnetic alloys is an essential building block for ultrafast spintronics. Very different element-specific demagnetization dynamics is believed to be a hard limit for switching in ferrimagnets. This suggests that ferrimagnets composed of two ions of different nature, such as rare earth transition metal alloys, are necessary for switching. However, experimental observation of toggle switching in Mn$_2$Ru$_x$Ga Heusler alloys, has contested this limit since Mn ions are of the same nature. To shed some light into this question, we present an atomis…
Energy-efficient control of magnetization without the help of a magnetic field is a key goal of spintronics. Purely heat-induced single-pulse all-optical toggle switching has been demonstrated, but so far only in Gd based amorphous ferrimagnet films. In this work, we demonstrate toggle switching in the half-metallic compensated ferrimagnetic Heusler alloys Mn2RuxGa, which have two crystallographically-inequivalent Mn sublattices. Moreover, we observe the switching at room temperature in samples that are immune to external magnetic fields in excess of 1 T, provided they exhibit compensation abo…
Spintronics provides an efficient platform for realizing non-volatile memory and logic devices. In these systems, data is stored in the magnetization of magnetic materials, and magnetization is switched in the writing process. In conventional spintronic devices, ferromagnetic materials are used which have a magnetization dynamics timescale of around the nanoseconds, setting a limit for the switching speed. Increasing the magnetization switching speed has been one of the challenges in spintronic research. In this work we take advantage of the ultrafast magnetization dynamics in ferrimagnetic ma…
We review and discuss the process of single-shot helicity-independent all-optical switching of magnetization by which a single suitably-ultrafast excitation, under the right conditions, toggles magnetization from one stable state to another. For almost a decade, this phenomenon was only consistently observed in specific rare-earth-transition-metal ferrimagnetic alloys of GdFeCo, but breakthrough experiments in recent years have revealed that the same behavior can be achieved in a wide range of multi-sublattice magnets including TbCo alloys doped with minute amounts of Gd, Gd/Co and Tb/Co synth…
研究了富过渡金属（TM）和富稀土（RE）两种结构的亚铁磁性Gd $_x$（Fe $_{90}$ Co $_{10}$）$_{100-x}$薄膜的自旋-轨道转矩开关。自旋-轨道扭矩驱动的磁化切换遵循相同的偏手性在TM-丰富和RE-丰富的样品相对于总磁化，但偏手性的切换是相反的相对于TM磁化。这表明自旋-轨道-转矩驱动的磁切换的符号遵循总磁化，尽管基于输运的技术（诸如异常霍尔效应）仅对过渡金属磁化敏感。这些结果为研究反铁磁耦合亚晶格材料中自旋角动量转移的物理性质提供了重要的理论依据。
We measured the spin-orbit torques (SOTs), current-induced switching, and domain wall (DW) motion in synthetic ferrimagnets consisting of Co/Tb layers with differing stacking order grown on a Pt underlayer. We find that the SOTs, magnetic anisotropy, compensation temperature and SOT-induced switching are highly sensitive to the stacking order of Co and Tb and to the element in contact with Pt. Our study further shows that Tb is an efficient SOT generator when in contact with Co, such that its position in the stack can be adjusted to generate torques additive to those generated by Pt. With opti…
We report on an element- and time-resolved investigation of femtosecond laser induced ultrafast dynamics of 3d and 4f spins in a ferrimagnetic Co80Dy20 alloy as a function of temperature. We observe an increase of the Co3d characteristic demagnetization time and a decrease of the Dy4f demagnetization time when the temperature is approaching the Curie temperature. It suggests that the critical slowing down regime, which affects the laser induced ultrafast dynamics in pure 3d transition metals and 4f rare-earth ferromagnetic layers, vanishes for the Dy sublattice in the CoDy alloy, in line with …
Orbital Hall Effect Enables Field-Free Magnetization Reversal in Ferrimagnets without Additional Conversion Layer
State Key Laboratory of Semiconductor Physics and Chip Technologies, Institute of Semiconductors, Chinese Academy of Sciences（中国科学院半导体研究所）；Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences（中国科学院大学材料科学与光电技术研究中心）；School of Physics, Huazhong University of Science and Technology（华中科技大学物理学院）；School of Materials Science and Engineering, Shandong University（山东大学材料科学与工程学院）
All-optical spin switching (AOS) represents a new frontier in magnetic storage technology -- spin manipulation without a magnetic field, -- but its underlying working principle is not well understood. Many AOS ferrimagnets such as GdFeCo are amorphous and renders the high-level first-principles study unfeasible. The crystalline half-metallic Heusler Mn$_2$RuGa presents an opportunity. Here we carry out hitherto the comprehensive density functional investigation into the material properties of Mn$_2$RuGa, and introduce two concepts - the spin anchor site and the optical active site - as two pil…
Recently, magnetic skyrmion has emerged as an active topic of fundamental study and applications in magnetic materials research. Magnetic skyrmions are vortex-like spin excitations with topological protection and therefore are more robust to pinning compared with magnetic domain walls. We employ atomistic simulations to create room-temperature ultra-small Neel skyrmions in amorphous ferrimagnet. The fast propagation and low-dissipation dynamics of ultra-small ferrimagnetic skyrmions make them attractive for utilization as an alternative to domain walls in spin-based memory and logic devices.
Ferrimagnets containing several partially compensated magnetic sublattices are considered the most promising materials for all-optical data storage and for ultrafast communications based on spin waves. There are two magnetic phases of the ferrimagnets: collinear and non-collinear ones. Up to now spin dynamics in ferrimagnets has been studied mostly in the collinear state without paying much attention to the kind of the magnetic phase. Here we investigate laser induced ultrafast spin dynamics in a rare-earth iron garnet film in the noncollinear phase as well. We identify a crucial influence of …
Geometry-Driven Magnetoelectric Coupling in Two-Dimensional Compensated Ferrimagnets
School of Emerging Technology and Hefei National Research Center for Physical Sciences at the Microscale, University of Science and Technology of China（中国科学技术大学新兴技术学院与微观物质科学国家研究中心）；State Key Laboratory of Precision and Intelligent Chemistry, School of Chemistry and Materials Science, and Collaborative Innovation Center of Chemistry for Energy Materials (iChEM), University of Science and Technology of China（中国科学技术大学精密与智能化学国家重点实验室、化学与材料科学学院及能源材料化学协同创新中心）；Hefei National Laboratory, University of Science and Technology of China（中国科学技术大学合肥国家实验室）
Manipulation of the intersublattice interaction strengh (JRE-TM) in rare earth (RE)-transition metal (TM) alloys is a key issue to understand how efficiently the laser-induced angular momentum transfers from 3d to 4f spins and to have a better control of the ultrafast spin dynamics. In this work, the relationships between laser-induced demagnetization process and the intersublattice 3d-4f interaction for the GdCoFe alloys were systematically studied. The ultrafast two-stage demagnetization process could change into a one-stage mode as the angular momentum transferring channel between 3d and 4f…
Measurements of the transverse Hall resistance are widely used to investigate electron transport, magnetization phenomena, and topological quantum states. Owing to the difficulty of probing transient changes of the transverse resistance, the vast majority of Hall effect experiments are carried out in stationary conditions using either dc or ac currents. Here we present an approach to perform time-resolved measurements of the transient Hall resistance during current-pulse injection with sub-nanosecond temporal resolution. We apply this technique to investigate in real-time the magnetization rev…
Laser induced ultrafast Co 3d and Ho 4f spin dynamics in CoHo ferrimagnetic alloys
Helmholtz-Zentrum Berlin für Materialien und Energie（柏林亥姆霍兹材料与能源中心）；Institut Jean Lamour, Université de Lorraine（洛林大学让·拉缪尔研究所）；Université de Strasbourg, CNRS, Institut de Physique et Chimie des Matériaux de Strasbourg（斯特拉斯堡大学、法国国家科学研究中心、斯特拉斯堡物理与化学材料研究所）
We study the demagnetization dynamics of the fully compensated half-metallic ferrimagnet Mn$_2$Ru$_x$Ga. While the two antiferromagnetically coupled sublattices are both composed of manganese, they exhibit different temperature dependencies due to their differing local environments. The sublattice magnetization dynamics triggered by femtosecond laser pulses are studied to reveal the roles played by the spin and intersublattice exchange. We find a two-step demagnetization process, similar to the well-established case of Gd(FeCo)$_3$, where the two Mn-sublattices have different demagnetization r…
In this work, we present evidence for the existence of a magnonic current on the sub-picosecond time-scale in a ferrimagnetic bilayer and its effect on ultrafast spin dynamics. The ferrimagnet, GdFeCo, is a material known to undergo ultrafast switching within 1-2ps after excitation with femtosecond laser pulses. Here, we show that the strong thermal gradients induced by applying femtosecond laser pulses and the presence of chemical inhomogeneities lead to local imbalances in the effective temperatures of the spins that produces a rapid transfer of spin angular momentum, which we interpret as a…
