Spin-lattice relaxation time of ferromagnetic gadolinium determined with time-resolved spin-polarized photoemission

Vaterlaus, A.; Beutler, Thomas C.; Meier, F.

doi:10.1103/physrevlett.67.3314

Cited by 157 publications

(113 citation statements)

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“…Both experimentally and theoretically the ultrashort time behavior of spin dynamics in transition metals is a new and challenging area. Vaterlaus et al [1] were the first to study the spin dynamics in ferromagnetic Gd. Employing spin-and time-resolved photo-emission with 60 ps probe pulses they found a spin-lattice relaxation (SLR) of 100±80 ps.…”

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“…The diagonal element |χ (1) zz | of the optical susceptibility mainly reflects the contribution from the charge dynamics while |χ (1) xy | mostly reflects the contribution from the spin dynamics. With the help of those two functions, we are able to address the different characters of the charge and spin dynamics separately.…”

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“…In Figs. 1 (b) and (d), |χ (1) xy (ω, t)| and |χ (1) zz (ω, t)|, as measured by typical pumpprobe experiments, are shown, which represent the spin and charge dynamics, respectively. ω = 2 eV hereafter.…”

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Ultrafast spin dynamics in nickel

Hübner

Zhang

1998

Phys. Rev. B

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The spin dynamics in Ni is studied by an exact diagonalization method on the ultrafast time scale. It is shown that the femtosecond relaxation of the magneto-optical response results from exchange interaction and spin-orbit coupling. Each of the two mechanisms affects the relaxation process differently. We find that the intrinsic spin dynamics occurs during about 10 fs while extrinsic effects such as laser-pulse duration and spectral width can slow down the observed dynamics considerably. Thus, our theory indicates that there is still room to accelerate the spin dynamics in experiments.PACS numbers: 75.40. Gb, 78.20.Ls, 78.47.+p The potential application of ferromagnetic materials on ultrafast time scales is attractive for information storage. Both experimentally and theoretically the ultrashort time behavior of spin dynamics in transition metals is a new and challenging area. Vaterlaus et al. [1] were the first to study the spin dynamics in ferromagnetic Gd. Employing spin-and time-resolved photo-emission with 60 ps probe pulses they found a spin-lattice relaxation (SLR) of 100±80 ps. Using femtosecond optical and magneto-optical pump-probe techniques, Beaurepaire et al [2] have studied the relaxation processes of electrons and spins in ferromagnetic Ni. They reported that the magnetization of a 22 nm thick film drops rapidly during the first picosecond and reaches its minimum after 2 ps. Recently, by time-resolved second harmonic generation (SHG), Hohlfeld et al. [3] found that even when electrons and lattice have not reached a common thermal equilibrium, the classical M (T ) curve can be reproduced for delay times longer than the electron thermalization time of about 280 fs. On the other hand, the transient magnetization reaches its minimum ≈ 50 fs before electron thermalization. Both groups used polycrystalline Ni but different pulse durations: 60 fs [2] vs 150 fs [3]. Recently even faster spin decays have been observed [4].At present, not even the mechanism for this ultrafast spin relaxation is known. Moreover, it is of great importance to know whether these results already reflect the intrinsic spin relaxation time scale or not. Theoretically, even the static ferromagnetism in transition metals has been a challenging topic as the electron correlation is very strong in these systems [5]. The theoretical treatment of the spin dynamics is limited. On the longer time scales, SLR been studied previously [6], and the theory yielded a relaxation time of 48 ps for Gd, in good agreement with the above mentioned experiment [1]. On this time scale, the main contribution results from anisotropic phononmagnon interaction. To our knowledge, so far no theoretical study has been performed about the spin dynamics of transition metals on the femtosecond time scale, which is apparently needed.For the theoretical description of ultrafast nonequilibrium charge and spin dynamics, one can either rely on the Baym-Kadanoff-Keldysh Green's function approach [7] or employing an exact diagonalization framework. In this Letter, we ...

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Ultrafast spin dynamics in nickel

Hübner

Zhang

1998

Phys. Rev. B

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“…Typically in a molecular magnet system an electronic T 1 relaxation time of 10 6 ns at 2 K may drop to 10 2 ns at 10 K and so on, relaxation time empirically varying as T −1 (Bogani & Wernsdorfer, 2008). In the solid state, the characteristic time for establishing thermal equilibrium between the lattice and the spin of ferromagnetic gadolinium was estimated to 0·1 ns at 45 K (Vaterlaus et al 1991). Experiments with nitrogen-vacancy (N-V) centers in diamond indicate that N-V center ensembles may have spincoherence times as long as 50 µs at room temperature (Epstein et al 2005), but generally in liquids relaxation varies as T −1 , typically from 0·1 ns at −40°C to 0·01 ns at 50°C (Zager & Freed, 1982).…”

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Quantum entanglement: facts and fiction – how wrong was Einstein after all?

Nordén

2016

Quart. Rev. Biophys.

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Abstract. Einstein was wrong with his 1927 Solvay Conference claim that quantum mechanics is incomplete and incapable of describing diffraction of single particles. However, the Einstein-Podolsky-Rosen paradox of entangled pairs of particles remains lurking with its 'spooky action at a distance'. In molecules quantum entanglement can be viewed as basis of both chemical bonding and excitonic states. The latter are important in many biophysical contexts and involve coupling between subsystems in which virtual excitations lead to eigenstates of the total Hamiltonian, but not for the separate subsystems. The author questions whether atomic or photonic systems may be probed to prove that particles or photons may stay entangled over large distances and display the immediate communication with each other that so concerned Einstein. A dissociating hydrogen molecule is taken as a model of a zero-spin entangled system whose angular momenta are in principle possible to probe for this purpose. In practice, however, spins randomize as a result of interactions with surrounding fields and matter. Similarly, no experiment seems yet to provide unambiguous evidence of remaining entanglement between single photons at large separations in absence of mutual interaction, or about immediate (superluminal) communication. This forces us to reflect again on what Einstein really had in mind with the paradox, viz. a probabilistic interpretation of a wave function for an ensemble of identically prepared states, rather than as a statement about single particles. Such a prepared state of many particles would lack properties of quantum entanglement that make it so special, including the uncertainty upon which safe quantum communication is assumed to rest. An example is Zewail's experiment showing visible resonance in the dissociation of a coherently vibrating ensemble of NaI molecules apparently violating the uncertainty principle. Einstein was wrong about diffracting single photons where space-like anti-bunching observations have proven recently their non-local character and how observation in one point can remotely affect the outcome in other points. By contrast, long range photon entanglement with immediate, superluminal response is still an elusive, possibly partly misunderstood issue. The author proposes that photons may entangle over large distances only if some interaction exists via fields that cannot propagate faster than the speed of light. An experiment to settle this 'interaction hypothesis' is suggested.In 1935, Einstein, Podolsky and Rosen (EPR) presented a paradox, which seemed to imply a fundamental discrepancy between quantum and classical mechanics and which they meant proves that the former is not a 'complete theory' . Einstein (1936) elaborated on the theme with a more nuanced description later, in what sense he considers quantum mechanics (QM) incomplete. His concern that it is the way QM is applied to singular particulate systems rather than whether it is a correct theory, was my inspiration for revisiting these grounds a...

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“…The control of magnetization on short timescales has become an area of intense research and many methods are used to excite a magnetic system, including spin-currents 1,2 , magnetic fields 3 and optical pulses 4,5 . It also has recently become possible to drive individual nanometer scale magnetic elements far from equilibrium using spin-currents and probe their dynamical response.…”

Section: Pacs Numbersmentioning

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Time-resolved magnetic relaxation of a nanomagnet on subnanosecond time scales

Liu

Bedau

Sun³

et al. 2012

Phys. Rev. B

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We present a two-current-pulse temporal correlation experiment to study the intrinsic subnanosecond nonequilibrium magnetic dynamics of a nanomagnet during and following a pulse excitation. This method is applied to a model spin-transfer system, a spin valve nanopillar with perpendicular magnetic anisotropy. Two-pulses separated by a short delay (< 500 ps) are shown to lead to the same switching probability as a single pulse with a duration that depends on the delay. This demonstrates a remarkable symmetry between magnetic excitation and relaxation and provides a direct measurement of the magnetic relaxation time. The results are consistent with a simple finite temperature Fokker-Planck macrospin model of the dynamics, suggesting more coherent magnetization dynamics in this short time nonequilibrium limit than near equilibrium.

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Spin-lattice relaxation time of ferromagnetic gadolinium determined with time-resolved spin-polarized photoemission

Abstract: The characteristic time for establishing thermal equilibrium between the lattice and the spin system is 100± 80 ps in ferromagnetic gadolinium.

Cited by 157 publications

References 10 publications

Ultrafast spin dynamics in nickel

Ultrafast spin dynamics in nickel

Quantum entanglement: facts and fiction – how wrong was Einstein after all?

Time-resolved magnetic relaxation of a nanomagnet on subnanosecond time scales

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