| 1. |
- Alekhin, A., et al.
(författare)
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Magneto-optical properties of Au upon the injection of hot spin-polarized electrons across Fe/Au(001) interfaces
- 2019
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Ingår i: Journal of Physics. - : IOP PUBLISHING LTD. - 0953-8984 .- 1361-648X. ; 31:12
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate a novel method for the excitation of sizable magneto-optical effects in Au by means of the laser-induced injection of hot spin-polarized electrons in Au/Fe/MgO(001) heterostructures. It is based on the energy- and spin-dependent electron transmittance of Fe/Au interface which acts as a spin filter for non-thermalized electrons optically excited in Fe. We show that after crossing the interface, majority electrons propagate through the Au layer with the velocity on the order of 1 nm fs(-1) (close to the Fermi velocity) and the decay length on the order of 100nm. Featuring ultrafast functionality and requiring no strong external magnetic fields, spin injection results in a distinct magneto-optical response of Au. We develop a formalism based on the phase of the transient complex MOKE response and demonstrate its robustness in a plethora of experimental and theoretical MOKE studies on Au, including our ab initio calculations. Our work introduces a flexible tool to manipulate magneto-optical properties of metals on the femtosecond timescale that holds high potential for active magneto-photonics, plasmonics, and spintronics.
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| 2. |
- Bajaj, Ashima, et al.
(författare)
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Anomalous Effect of Quantum Interference in Organic Spin Filters
- 2020
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Ingår i: The Journal of Physical Chemistry C. - : AMER CHEMICAL SOC. - 1932-7447 .- 1932-7455. ; 124:44, s. 24361-24371
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Tidskriftsartikel (refereegranskat)abstract
- The molecular topology in the single-molecule nanojunctions through which the de Broglie wave propagates plays a crucial role in controlling the molecular conductance. The enhancement and reduction of the conductance in para- and meta-connected molecules due to constructive and destructive quantum interference (QI), respectively, are quite well established. Herein, we investigated the effect of localized spin centers on spin transportation using organic radicals as molecular junctions. The role of the localized spins on the QI as well as on spin filtering capability is investigated employing density functional theory in combination with nonequilibrium Green's function (NEGF-DFT) techniques. Various organic radicals including nitroxy (NO center dot), phenoxy (PO center dot), and methyl (CH2 center dot) attached to the central benzene ring of pentacene with different terminal connections (para and meta) to gold electrodes are examined. Due to more obvious QI effects, para-connected pentacene is found to be more conductive than the meta one. Surprisingly, on incorporating a radical center, along with spin filtering, a significant reversal of QI effects is observed which manifests itself in such a way that the conductance of meta-coupled radicals is found to be more than para-coupled ones by 2 orders of magnitude. The anomaly in QI patterns induced by the radical center is analyzed and discussed in terms of orbital and structural perspectives.
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| 3. |
- Berritta, Marco, et al.
(författare)
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Ab Initio Theory of Coherent Laser-Induced Magnetization in Metals
- 2016
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 117:13
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Tidskriftsartikel (refereegranskat)abstract
- We present the first materials specific ab initio theory of the magnetization induced by circularly polarized laser light in metals. Our calculations are based on nonlinear density matrix theory and include the effect of absorption. We show that the induced magnetization, commonly referred to as inverse Faraday effect, is strongly materials and frequency dependent, and demonstrate the existence of both spin and orbital induced magnetizations which exhibit a surprisingly different behavior. We show that for nonmagnetic metals (such as Cu, Au, Pd, Pt) and antiferromagnetic metals the induced magnetization is antisymmetric in the light's helicity, whereas for ferromagnetic metals (Fe, Co, Ni, FePt) the imparted magnetization is only asymmetric in the helicity. We compute effective optomagnetic fields that correspond to the induced magnetizations and provide guidelines for achieving all-optical helicity-dependent switching.
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| 4. |
- Berritta, Marco, et al.
(författare)
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Interplay between quantum interference and conformational fluctuations in single-molecule break junctions
- 2015
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Ingår i: Nanoscale. - : Royal Society of Chemistry (RSC). - 2040-3364 .- 2040-3372. ; 7:3, s. 1096-1101
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Tidskriftsartikel (refereegranskat)abstract
- We theoretically explored the combined role of conformational fluctuations and quantum interference in determining the electrical conductance of single-molecule break junctions. In particular we computed the conductance of a family of methylsulfide-functionalized trans-alpha,omega-diphenyloligoene molecules, with terminal phenyl rings containing meta or para linkages, for which (at least in the absence of fluctuations) destructive interference in the former is expected to decrease their electrical conductance compared with the latter. We compared the predictions of density functional theory (DFT), in which fluctuational effects are absent, with results for the conformationally-averaged conductance obtained from an ensemble of conformations obtained from classical molecular dynamics. We found that junctions formed from these molecules exhibit distinct transport regimes during junction evolution and the signatures of quantum interference in these molecules survive the effect of conformational fluctuations. Furthermore, the agreement between theory and experiment is significantly improved by including conformational averaging.
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| 5. |
- Ciuciulkaite, Agne, MSc, 1991-, et al.
(författare)
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Magnetic and all-optical switching properties of amorphous TbxCo100-x alloys
- 2020
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Ingår i: Physical Review Materials. - : American Physical Society (APS). - 2475-9953. ; 4:10
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Tidskriftsartikel (refereegranskat)abstract
- Amorphous TbxCo100-x magnetic alloys exhibit a list of intriguing properties, such as perpendicular magnetic anisotropy, high magneto-optical activity, and magnetization switching using ultrashort optical pulses. Varying the Tb:Co ratio in these alloys allows for tuning properties such as the saturation magnetic moment, coercive field, and the performance of light-induced magnetization switching. In this paper, we investigate the magnetic, optical, and magneto-optical properties of various TbxCo100-x thin-film alloy compositions. We report on the effect the choice of different seeding layers has on the structural and magnetic properties of TbxCo100-x layers. We also demonstrate that for a range of alloys, deposited on fused silica substrates, with Tb content of 24-30 at. %, helicity-dependent all-optical switching of magnetization can be achieved, albeit in a multishot framework. We explain this property to arise from the helicity-dependent laser-induced magnetization on the Co sublattice due to the inverse Faraday effect. Our paper provides an insight into material aspects for future potential hybrid magnetoplasmonic TbCo-based architectures.
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| 6. |
- Dannegger, Tobias, et al.
(författare)
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Ultrafast coherent all-optical switching of an antiferromagnet with the inverse Faraday effect
- 2021
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Ingår i: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 104:6
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Tidskriftsartikel (refereegranskat)abstract
- We explore the possibility of ultrafast, coherent all-optical magnetization switching in antiferromagnets by studying the action of the inverse Faraday effect in CrPt, an easy-plane antiferromagnet. Using a combination of density-functional theory and atomistic spin dynamics simulations, we show how a circularly polarized laser pulse can switch the order parameter of the antiferromagnet within a few hundred femtoseconds. This nonthermal switching takes place on an elliptical path, driven by the staggered magnetic moments induced by the inverse Faraday effect and leading to reliable switching between two perpendicular magnetic states.
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| 7. |
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| 8. |
- Hofherr, M., et al.
(författare)
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Speed and efficiency of femtosecond spin current injection into a nonmagnetic material
- 2017
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Ingår i: Physical Review B. - : AMER PHYSICAL SOC. - 2469-9950 .- 2469-9969. ; 96:10
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Tidskriftsartikel (refereegranskat)abstract
- We investigate femtosecond spin injection from an optically excited Ni top layer into an Au bottom layer using time-resolved complex magneto-optical Kerr effect (C-MOKE) measurements. Employing the C-MOKE formalism, we are able to follow layer-resolved demagnetization in Ni and the simultaneous spin injection into the adjacent Au film, both occurring within similar to 40 fs. We confirm the ballistic to diffusive propagation of the spin transfer process with ab initio theory and superdiffusive transport calculations. In particular, our combined experimental-theoretical effort does allow us to quantify the so far elusive amount of spin injection, and therefore the spin injection efficiency at the interface.
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| 9. |
- John, R., et al.
(författare)
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Magnetisation switching of FePt nanoparticle recording medium by femtosecond laser pulses
- 2017
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Ingår i: Scientific Reports. - : NATURE PUBLISHING GROUP. - 2045-2322. ; 7
-
Tidskriftsartikel (refereegranskat)abstract
- Manipulation of magnetisation with ultrashort laser pulses is promising for information storage device applications. The dynamics of the magnetisation response depends on the energy transfer from the photons to the spins during the initial laser excitation. A material of special interest for magnetic storage are FePt nanoparticles, for which switching of the magnetisation with optical angular momentum was demonstrated recently. The mechanism remained unclear. Here we investigate experimentally and theoretically the all-optical switching of FePt nanoparticles. We show that the magnetisation switching is a stochastic process. We develop a complete multiscale model which allows us to optimize the number of laser shots needed to switch the magnetisation of high anisotropy FePt nanoparticles in our experiments. We conclude that only angular momentum induced optically by the inverse Faraday effect will provide switching with one single femtosecond laser pulse.
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| 10. |
- Lyalin, Igor, et al.
(författare)
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Magneto-Optical Detection of the Orbital Hall Effect in Chromium
- 2023
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Ingår i: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 131:15
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Tidskriftsartikel (refereegranskat)abstract
- The orbital Hall effect has been theoretically predicted but its direct observation is a challenge. Here, we report the magneto-optical detection of current-induced orbital accumulation at the surface of a light 3d transition metal, Cr. The orbital polarization is in-plane, transverse to the current direction, and scales linearly with current density, consistent with the orbital Hall effect. Comparing the thickness-dependent magneto-optical measurements with ab initio calculations, we estimate an orbital diffusion length in Cr of 6.6 +/- 0.6nm.
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| 11. |
- Mondal, Ritwik, et al.
(författare)
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Ab initio investigation of light-induced relativistic spin-flip effects in magneto-optics
- 2015
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 91:17
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Tidskriftsartikel (refereegranskat)abstract
- Excitation of a metallic ferromagnet such as Ni with an intensive femtosecond laser pulse causes an ultrafast demagnetization within approximately 300 fs. It was proposed that the ultrafast demagnetization measured in femtosecond magneto-optical experiments could be due to relativistic light-induced processes. We perform an ab initio investigation of the influence of relativistic effects on the magneto-optical response of Ni. To this end, first, we develop a response theory formulation of the additional appearing ultrarelativistic terms in the Foldy-Wouthuysen transformed Dirac Hamiltonian due to the electromagnetic field, and second, we compute the influence of relativistic light-induced spin-flip transitions on the magneto-optics. Our ab initio calculations of relativistic spin-flip optical excitations predict that these can give only a very small contribution (<= 0.1%) to the laser-induced magnetization change in Ni.
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| 12. |
- Mondal, Ritwik, et al.
(författare)
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Generalisation of Gilbert damping and magnetic inertia parameter as a series of higher-order relativistic terms
- 2018
-
Ingår i: Journal of Physics. - 0953-8984 .- 1361-648X. ; 30:26
-
Tidskriftsartikel (refereegranskat)abstract
- The phenomenological Landau-Lifshitz-Gilbert (LLG) equation of motion remains as the cornerstone of contemporary magnetisation dynamics studies, wherein the Gilbert damping parameter has been attributed to first-order relativistic effects. To include magnetic inertial effects the LLG equation has previously been extended with a supplemental inertia term; the arising inertial dynamics has been related to second-order relativistic effects. Here we start from the relativistic Dirac equation and, performing a Foldy-Wouthuysen transformation, derive a generalised Pauli spin Hamiltonian that contains relativistic correction terms to any higher order. Using the Heisenberg equation of spin motion we derive general relativistic expressions for the tensorial Gilbert damping and magnetic inertia parameters, and show that these tensors can be expressed as series of higher-order relativistic correction terns. We further show that, in the case of a harmonic external driving field, these series can be summed and we provide closed analytical expressions for the Gilbert and inertial parameters that are functions of the frequency of the driving field.
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| 13. |
- Mondal, Ritwik, et al.
(författare)
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On the origin of magnetic inertia : a rigorous relativistic Dirac theory derivation
- 2018
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Ingår i: SPINTRONICS XI. - : SPIE-INT SOC OPTICAL ENGINEERING. - 9781510620360
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Konferensbidrag (refereegranskat)abstract
- Inertia is a fundamental property of a particle that can be understood from Newtons laws of motion. In a similar way, any magnetized body must possess magnetic inertia by the virtue of its magnetization. The influence of possible magnetic inertia effects has recently drawn attention in ultrafast magnetization dynamics and switching. Magnetization dynamics at the inertial regime has been investigated using thermodynamic theories that predicted the magnetic inertia can become impactful at shorter timescales. However, at the fundamental level, the origin of magnetic inertial dynamics is still unknown. Here, we derive rigorously a description of magnetic inertia in the extended Landau-Lifshitz-Gilbert (LLG) equation starting from a fundamental and relativistic Dirac-Kohn-Sham framework. We use a unitary transformation, the so called called Foldy-Wouthuysen transformation, up to the order of 1/c(4). In this way, the particle and anti-particle in fully relativistic description become decoupled and a Hamiltonian describing only the particles is derived. This Hamiltonian involves the nonrelativistic Schrodinger-Pauli Hamiltonian together with the relativistic corrections of the order 1/c(2) and 1/c(4.) With the thus-derived Hamiltonian, we calculate the corresponding spin dynamics leading to the LLG equation of motion. Our result exemplify that the relativistic correction terms of 1/c(2) are responsible for the Gilbert damping, however, the relativistic correction terms of 1/c(4) are responsible for magnetic inertial dynamics. Therefore, we predict that the intrinsic magnetic inertia is a higher-order relativistic spin-orbit coupling effect and is expected to be prominent only on ultrashort timescales (subpicoseconds). We also show that the corresponding Gilbert damping and magnetic inertia parameters are related to one another through the imaginary and real parts of the magnetic susceptibility tensor, respectively.
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| 14. |
- Mondal, Ritwik, et al.
(författare)
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Relativistic interaction Hamiltonian coupling the angular momentum of light and the electron spin
- 2015
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 92:10
-
Tidskriftsartikel (refereegranskat)abstract
- On the basis of the Dirac equation, a relativistic interaction Hamiltonian is derived which linearly couples the angular momentum density j of the electromagnetic (EM) field and the electron's spin sigma. The expectation value of this novel Hamiltonian is demonstrated to be precisely the recently proposed energy coupling the EM angular momentum density and magnetic moments [A. Raeliarijaona et al., Phys. Rev. Lett. 110, 137205 (2013)]. This previously overlooked Hamiltonian is also found to naturally result in the exact analytical form of the interaction energy inherent to the inverse Faraday effect, therefore demonstrating its relevance and easy use for the derivation of other complex magneto-optical and magnetoelectric effects originating from electron spin-light angular momentum couplings.
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| 15. |
- Mondal, Ritwik, et al.
(författare)
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Relativistic theory of magnetic inertia in ultrafast spin dynamics
- 2017
-
Ingår i: Physical review B: covering condensed matter and materials physics. - 2469-9950 .- 2469-9969. ; 96:2
-
Tidskriftsartikel (refereegranskat)abstract
- The influence of possible magnetic inertia effects has recently drawn attention in ultrafast magnetization dynamics and switching. Here we derive rigorously a description of inertia in the Landau-Lifshitz-Gilbert equation on the basis of the Dirac-Kohn-Sham framework. Using the Foldy-Wouthuysen transformation up to the order of 1/c(4) gives the intrinsic inertia of a pure system through the second order time derivative of magnetization in the dynamical equation of motion. Thus, the inertial damping I is a higher order spin-orbit coupling effect, similar to 1/c(4), as compared to the Gilbert damping Gamma that is of order 1/c(2). Inertia is therefore expected to play a role only on ultrashort timescales (subpicoseconds). We also show that the Gilbert damping and inertial damping are related to one another through the imaginary and real parts of the magnetic susceptibility tensor, respectively.
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| 16. |
- Mondal, Ritwik, et al.
(författare)
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Relativistic theory of spin relaxation mechanisms in the Landau-Lifshitz-Gilbert equation of spin dynamics
- 2016
-
Ingår i: Physical Review B. - 2469-9950 .- 2469-9969. ; 94:14
-
Tidskriftsartikel (refereegranskat)abstract
- Starting from the Dirac-Kohn-Sham equation, we derive the relativistic equation of motion of spin angular momentum in a magnetic solid under an external electromagnetic field. This equation of motion can be rewritten in the form of the well-known Landau-Lifshitz-Gilbert equation for a harmonic external magnetic field and leads to a more general magnetization dynamics equation for a general time-dependent magnetic field. In both cases there is an electronic spin-relaxation term which stems from the spin-orbit interaction. We thus rigorously derive, from fundamental principles, a general expression for the anisotropic damping tensor which is shown to contain an isotropic Gilbert contribution as well as an anisotropic Ising-like and a chiral, Dzyaloshinskii-Moriya-like contribution. The expression for the spin relaxation tensor comprises furthermore both electronic interband and intraband transitions. We also show that when the externally applied electromagnetic field possesses spin angular momentum, this will lead to an optical spin torque exerted on the spin moment.
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| 17. |
- Mondal, Ritwik, et al.
(författare)
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Signatures of relativistic spin-light coupling in magneto-optical pump-probe experiments
- 2017
-
Ingår i: Journal of Physics. - : IOP PUBLISHING LTD. - 0953-8984 .- 1361-648X. ; 29:19
-
Tidskriftsartikel (refereegranskat)abstract
- Femtosecond magneto-optical pump-probe measurements of ultrafast demagnetization show an intriguing difference in the first 100 fs of the magneto-optical Kerr response depending on whether the polarization of the pump and probe beams are in parallel or perpendicular configuration (Bigot et al 2009 Nat. Phys. 5 515). Starting from a most general relativistic Hamiltonian we focus on the ultra-relativistic light-spin interaction and show that this coupling term leads to different light-induced opto-magnetic fields when pump and probe polarization are parallel and perpendicular to each other, providing thus an explanation for the measurements. We also analyze other pump-probe configurations where the pump laser is circularly polarized and the employed probe contains only linearly polarized light and show that similar opto-magnetic effects can be anticipated.
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| 18. |
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| 19. |
- Mondal, Ritwik, et al.
(författare)
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Unified theory of magnetization dynamics with relativistic and nonrelativistic spin torques
- 2018
-
Ingår i: Physical Review B. - 2469-9950 .- 2469-9969. ; 98:21
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Tidskriftsartikel (refereegranskat)abstract
- Spin torques play a crucial role in operative properties of modern spintronic devices. To study current-driven magnetization dynamics, spin-torque terms providing the action of spin-polarized currents have previously often been added in a phenomenological way to the Landau-Lifshitz-Gilbert equation describing the local spin dynamics, yet without derivation from fundamental principles. Here, starting from the Dirac-Kohn-Sham theory and incorporating nonlocal spin transport we rigorously derive the various spin-torque terms that appear in current-driven magnetization dynamics. In particular we obtain an extended magnetization dynamics equation that precisely contains the nonrelativistic adiabatic and relativistic nonadiabatic spin-transfer torques of the Berger and Zhang-Li forms as well as relativistic spin-orbit torques. We derive in addition a previously unnoticed relativistic spin-torque term and moreover show that the various obtained spin-torque terms do not appear in the same mathematical form in both the Landau-Lifshitz and Landau-Lifshitz-Gilbert equations of spin dynamics.
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| 20. |
- Paillard, Charles, et al.
(författare)
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New relativistic Hamiltonian : the Angular MagnetoElectric coupling
- 2016
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Ingår i: Spintronics IX. - : SPIE. - 9781510602540
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Konferensbidrag (refereegranskat)abstract
- Spin-Orbit Coupling (SOC) is a ubiquitous phenomenon in the spintronics area, as it plays a major role in allowing or enhancing many well-known phenomena, such as the Dzyaloshinskii-Moriya interaction, magnetocrystalline anisotropy, the Rashba effect, etc. However, the usual expression of the SOC interaction h/4 m(2)c(2) [E x p] . sigma (1) where p is the momentum operator, E the electric field, sigma the vector of Pauli matrices, breaks the gauge invariance required by the electronic Hamiltonian. On the other hand, very recently, a new phenomenological interaction, coupling the angular momentum of light and magnetic moments, has been proposed based on symmetry arguments: -xi/2[r x (E x B)] . M, (2) with M the magnetization, r the position, and xi the interaction strength constant. This interaction has been demonstrated to contribute and/or give rise, in a straightforward way, to various magnetoelectric phenomena, such as the anomalous Hall effect (AHE), the anisotropic magnetoresistance (AMR), the planar Hall effect and Rashba-like effects, or the spin -current model in multiferroics. This last model is known to be the origin of the cycloidal spin arrangement in bismuth ferrite for instance. However, the coupling of the angular momentum of light with magnetic moments lacked a fundamental theoretical basis. Starting from the Dirac equation, we derive a relativistic interaction Hamiltonian which linearly couples the angular momentum density of the electromagnetic (EM) field and the electrons spin ?. We name this coupling the Angular MagnetoElectric (AME) coupling. We show that in the limit of uniform magnetic field, the AME coupling yields an interaction exactly of the form of Eq. (2), thereby giving a firm theoretical basis to earlier works. The AME coupling can be expressed as: xi[E x A] . sigma-, (3) with A being the vector potential. Interestingly, the AME coupling was shown to be complementary to the traditional SOC, and together they restore the gauge invariance of the Hamiltonian. As an illustration of the AME coupling, we straightforwardly derived a relativistic correction to the so-called Inverse Faraday Effect (IFE), which is the emergence of an effective magnetic field under illumination by a circularly polarized light.
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| 21. |
- Salemi, Leandro, et al.
(författare)
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Orbitally dominated Rashba-Edelstein effect in noncentrosymmetric antiferromagnets
- 2019
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Ingår i: Nature Communications. - : NATURE PUBLISHING GROUP. - 2041-1723. ; 10
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Tidskriftsartikel (refereegranskat)abstract
- Efficient manipulation of magnetic order with electric current pulses is desirable for achieving fast spintronic devices. The Rashba-Edelstein effect, wherein spin polarization is electrically induced in noncentrosymmetric systems, provides a mean to achieve staggered spin-orbit torques. Initially predicted for spin, its orbital counterpart has been disregarded up to now. Here we report a generalized Rashba-Edelstein effect, which generates not only spin polarization but also orbital polarization, which we find to be far from being negligible. We show that the orbital Rashba-Edelstein effect does not require spin-orbit coupling to exist. We present first-principles calculations of the frequency-dependent spin and orbital Rashba-Edelstein tensors for the noncentrosymmetric antiferromagnets CuMnAs and Mn2Au. We show that the electrically induced local magnetization can exhibit Rashba-like or Dresselhaus-like symmetries, depending on the magnetic configuration. We compute sizable induced magnetizations at optical frequencies, which suggest that electric-field driven switching could be achieved at much higher frequencies.
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| 22. |
- Salemi, Leandro, et al.
(författare)
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Quantitative comparison of electrically induced spin and orbital polarizations in heavy-metal/3d-metal bilayers
- 2021
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Ingår i: Physical Review Materials. - : American Physical Society. - 2475-9953. ; 5:7
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Tidskriftsartikel (refereegranskat)abstract
- Electrical control of magnetization is of crucial importance for integrated spintronics devices. Spin-orbit torques (SOT) in heavy-metal/ferromagnetic heterostructures have emerged as a promising tool to achieve efficiently current-induced magnetization reversal. However, the microscopic origin of the SOT is being debated, with the spin Hall effect (SHE) due to nonlocal spin currents and the spin Rashba-Edelstein effect (SREE) due to local spin polarization at the interface being the primary candidates. We investigate the electrically induced out-of-equilibrium spin and orbital polarizations in pure Pt films and in Pt/3d-metal (Co, Ni, Cu) bilayer films using ab initio electronic structure methods and linear-response theory. We compute atom-resolved response quantities that allow us to identify the induced spin-polarization contributions that lead to fieldlike (FL) SOTs, mostly associated with the SREE, and dampinglike (DL) SOTs, mostly associated with the SHE, and compare their relative magnitude, dependence on the magnetization direction, as well as their Pt-layer thickness dependence. We find that both the FL and DL components contribute to the resulting SOT at the Pt/Co and Pt/Ni interfaces, with the former contributions being larger at the Pt interface layer and the latter larger in the Co or Ni layers. Our calculations show that the electrically induced transverse orbital polarization is exceedingly larger than the induced spin polarization and present even without spin-orbit coupling, in contrast to the spin polarization.
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| 23. |
- Seifert, Tom S., et al.
(författare)
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Frequency-Independent Terahertz Anomalous Hall Effect in DyCo5, Co32Fe68, and Gd27Fe73 Thin Films from DC to 40 THz
- 2021
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Ingår i: Advanced Materials. - : John Wiley & Sons. - 0935-9648 .- 1521-4095. ; 33:14
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Tidskriftsartikel (refereegranskat)abstract
- The anomalous Hall effect (AHE) is a fundamental spintronic charge-to-charge-current conversion phenomenon and closely related to spin-to-charge-current conversion by the spin Hall effect. Future high-speed spintronic devices will crucially rely on such conversion phenomena at terahertz (THz) frequencies. Here, it is revealed that the AHE remains operative from DC up to 40 THz with a flat frequency response in thin films of three technologically relevant magnetic materials: DyCo5, Co32Fe68, and Gd27Fe73. The frequency-dependent conductivity-tensor elements sigma(xx) and sigma(yx) are measured, and good agreement with DC measurements is found. The experimental findings are fully consistent with ab initio calculations of sigma(yx) for CoFe and highlight the role of the large Drude scattering rate (approximate to 100 THz) of metal thin films, which smears out any sharp spectral features of the THz AHE. Finally, it is found that the intrinsic contribution to the THz AHE dominates over the extrinsic mechanisms for the Co32Fe68 sample. The results imply that the AHE and related effects such as the spin Hall effect are highly promising ingredients of future THz spintronic devices reliably operating from DC to 40 THz and beyond.
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| 24. |
- Shokeen, Vishal, et al.
(författare)
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Real-time observation of non-equilibrium phonon-electron energy and angular momentum flow in laser-heated nickel
- 2024
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Ingår i: Science Advances. - : American Association For Cancer Research (AACR). - 2375-2548. ; 10:5
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Tidskriftsartikel (refereegranskat)abstract
- Identifying the microscopic nature of non-equilibrium energy transfer mechanisms among electronic, spin, and lattice degrees of freedom is central to understanding ultrafast phenomena such as manipulating magnetism on the femtosecond timescale. Here, we use time- and angle-resolved photoemission spectroscopy to go beyond the often-used ensemble-averaged view of non-equilibrium dynamics in terms of quasiparticle temperature evolutions. We show for ferromagnetic Ni that the non-equilibrium electron and spin dynamics display pronounced variations with electron momentum, whereas the magnetic exchange interaction remains isotropic. This highlights the influence of lattice-mediated scattering processes and opens a pathway toward unraveling the still elusive microscopic mechanism of spin-lattice angular momentum transfer.
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| 25. |
- Stamm, C., et al.
(författare)
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Magneto-Optical Detection of the Spin Hall Effect in Pt and W Thin Films
- 2017
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 119:8
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Tidskriftsartikel (refereegranskat)abstract
- The conversion of charge currents into spin currents in nonmagnetic conductors is a hallmark manifestation of spin-orbit coupling that has important implications for spintronic devices. Here we report the measurement of the interfacial spin accumulation induced by the spin Hall effect in Pt and W thin films using magneto-optical Kerr microscopy. We show that the Kerr rotation has opposite sign in Pt and W and scales linearly with current density. By comparing the experimental results with ab initio calculations of the spin Hall and magneto-optical Kerr effects, we quantitatively determine the current-induced spin accumulation at the Pt interface as 5×10−12 μB A−1 cm2 per atom. From thickness-dependent measurements, we determine the spin diffusion length in a single Pt film to be 11±3 nm, which is significantly larger compared to that of Pt adjacent to a magnetic layer.
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| 26. |
- Stiehl, Martin, et al.
(författare)
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All-optical switching in Cr- and Mn-doped L10 FePt thin films
- 2024
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Ingår i: Physical Review Applied. - : American Physical Society. - 2331-7019. ; 21:5
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Tidskriftsartikel (refereegranskat)abstract
- Optical manipulation of the magnetization of thin films opens up exciting possibilities for ever-faster magnetic storage applications. In this context, ?10 chemically ordered FePt thin films are of particular interest due to their high perpendicular magnetic anisotropy and their use as a storage material for heat-assisted magnetic recording devices. However, these materials are difficult to manipulate with external fields due to their high coercivity field. Thus, we want to explore the possibility of tailoring the properties of these materials to enable switching using all-optical techniques. While stochastic all-optical switching between partially magnetized states has been reported for undoped FePt thin films, we have investigated to what extent doping with third elements can influence the switching behavior. Reducing the saturation magnetization may be one way to facilitate all-optical switching. While this is expected with the introduction of additional elements, we also want to highlight the role of the inverse Faraday effect and the magnetic circular dichroism in stochastic all-optical switching. In this study, Cr was found to be a promising dopant, which can almost double the relative magnetization change of the partially magnetized states compared to pure FePt.
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| 27. |
- Yamamoto, Kohei, et al.
(författare)
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Ultrafast demagnetization of Pt magnetic moment in L1(0)-FePt probed by magnetic circular dichroism at a hard x-ray free electron laser
- 2019
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Ingår i: New Journal of Physics. - : IOP PUBLISHING LTD. - 1367-2630. ; 21:12
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Tidskriftsartikel (refereegranskat)abstract
- Unraveling the origin of ultrafast demagnetization in multisublattice ferromagnetic materials requires femtosecond x-ray techniques to trace the magnetic moment dynamics on individual elements, but this could not yet be achieved in the hard x-ray regime. We demonstrate here the first ultrafast demagnetization dynamics in the ferromagnetic heavy 5d-transition metal Pt using circularly-polarized hard x-rays at an x-ray free electron laser (XFEL). The decay time of laser-induced demagnetization of L1(0)-FePt is determined to be tau(Pt) = 0.61 +/- 0.04 ps using time-resolved x-ray magnetic circular dichroism at the Pt L-3 edge, whereas magneto-optical Kerr measurements indicate the decay time for the total magnetization as tau(total) < 0.1 ps. A transient magnetic state with a photomodulated ratio of the 3d and 5d magnetic moments is demonstrated for pump-probe delays larger than 1 ps. We explain this distinct photo-modulated transient magnetic state by the induced-moment behavior of the Pt atom and the x-ray probing depth. Our findings pave the way for the future use of XFELs to disentangle atomic spin dynamics contributions.
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