Spin-Flip Processes and Ultrafast Magnetization Dynamics in Co: Unifying the Microscopic and Macroscopic View of Femtosecond Magnetism

Cinchetti, Mirko; Albaneda, M. Sánchez; Hoffmann, D.; Roth, T.; Wüstenberg, Jan-Peter; Krauss, Michael I.; Andreyev, O.; Schneider, Hans Christian; Bauer, Michael; Aeschlimann, Martin

doi:10.1103/physrevlett.97.177201

Cited by 158 publications

(145 citation statements)

References 19 publications

(32 reference statements)

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“…1B) (18,(24)(25)(26)(27). These details of the scattering processes remain the subject of intense debate in ultrafast magnetism (7,24,25,(28)(29)(30)(31)(32)(33). Moreover, nonadiabatic heating processes of the electron, spin, and lattice subsystems on such ultrafast timescales, together with strongly nonequilibrium transient phase states, necessarily complicate our understanding of the underlying physics for ultrafast demagnetization.…”

Section: Discussionmentioning

confidence: 99%

Probing the timescale of the exchange interaction in a ferromagnetic alloy

Mathias

La-o-vorakiat

Grychtol

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

227

169

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The underlying physics of all ferromagnetic behavior is the cooperative interaction between individual atomic magnetic moments that results in a macroscopic magnetization. In this work, we use extreme ultraviolet pulses from high-harmonic generation as an element-specific probe of ultrafast, optically driven, demagnetization in a ferromagnetic Fe-Ni alloy (permalloy). We show that for times shorter than the characteristic timescale for exchange coupling, the magnetization of Fe quenches more strongly than that of Ni. Then as the Fe moments start to randomize, the strong ferromagnetic exchange interaction induces further demagnetization in Ni, with a characteristic delay determined by the strength of the exchange interaction. We can further enhance this delay by lowering the exchange energy by diluting the permalloy with Cu. This measurement probes how the fundamental quantum mechanical exchange coupling between Fe and Ni in magnetic materials influences magnetic switching dynamics in ferromagnetic materials relevant to next-generation data storage technologies.magnetism | quantum | ultrafast P rogress in magnetic information storage and processing technology is intimately associated with complex materials that are engineered at the nanometer scale. Heat-assisted magnetic recording (1), bit-patterned data storage media (2), all-optical magnetization reversal (3), and giant tunneling magnetoresistive disk drive read sensors are examples of such technologies (4). Next-generation devices will require that the magnetic state of materials be manipulated on fast timescales and at the nanometer level. However, a complete microscopic understanding of magnetization dynamics that involves the correlated interactions of spins, electrons, photons, and phonons on femtosecond timescales has yet to be developed. Two reasons for this lack of fundamental understanding of ultrafast magnetism at the microscopic scale are the complexity of the problem itself, as well as the experimental challenge of accessing ultrafast and element-specific magnetization dynamics. One approach for addressing the experimental challenge is to use X-ray magnetic circular dichroism (XMCD) employing X-rays generated by a synchrotron light source. XMCD has the inherent advantage of element-specific detection, and "sliced" synchrotron pulses are already used for ultrafast studies (5-9). In an alternative approach, we recently demonstrated that coherent extreme ultraviolet (XUV) beams from a tabletop high-harmonic source (10, 11) can also be used to probe ultrafast element-specific magnetization dynamics in permalloy (Ni 0.8 Fe 0.2 ) (12). For that demonstration, we took advantage of magnetic birefringence at the M-edge in transition metals to independently follow dynamics for Ni and Fe. However, the time resolution available in that initial experiment was insufficient to observe any differences in the response of the constituent elements on very short timescales.In this work, we experimentally answer the fundamental question of whether the magnetization dyn...

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Section: Discussionmentioning

confidence: 99%

Probing the timescale of the exchange interaction in a ferromagnetic alloy

Mathias

La-o-vorakiat

Grychtol

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

227

169

View full text Add to dashboard Cite

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“…The enhanced spin-orbit coupling at the Co/Pt or Co/Pd interfaces was shown to cause an increased rate of laser-induced demagnetization 18 compared to that of pure transition metal thin films. [14][15][16][17] Further, a dependence of the demagnetization rate on the thickness of the transition metal in the multilayers was detected. 19 The laser-induced magnetization reversal observed in these ferromagnetic materials 3 does not fit the paradigm of the existing understanding of AOS in ferrimagnets.…”

mentioning

confidence: 90%

Helicity and field dependent magnetization dynamics of ferromagnetic Co/Pt multilayers

Tsema¹,

Kichin²,

Hellwig

et al. 2016

Applied Physics Letters

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We present helicity and field dependent magnetization dynamics of ferromagnetic Co/Pt multilayers, suitable for all-optical helicity-dependent switching. Employing single-shot time-resolved magneto-optical Kerr effect imaging, our study demonstrates an ultra-fast quenching of the magnetization after a single 60 fs laser pulse excitation followed by a recovery. Full demagnetization occurs within 1 ps after laser excitation. The magnetization dynamics reveals a small helicity dependence caused by magnetic circular dichroism. When an external magnetic field is applied, a heat-assisted magnetization reversal occurs on a nanosecond time scale.

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“…Most of the proposed scenaria consider the spin-orbit coupling as a necessary component of the angular-momentum dissipation. [4][5][6][7][8][9] Recently, additional arguments have been suggested 5 supporting one such scenario: the Elliott-Yafet mechanism 10,11 of angularmomentum transfer between electrons and lattice. The efficiency of the Elliott-Yafet mechanism is determined by the parameter describing the spin mixing of the electron states due to spin-orbit coupling (SOC).…”

mentioning

confidence: 99%

Magnetic excitations and femtomagnetism of FeRh: A first-principles study

2011

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The paper is partly motivated by recent pump-probe experiments with ultrashort laser pulses on antiferromagnetic FeRh that have shown the generation of magnetization within a subpicosecond time scale. On the other hand, the physical mechanism of the thermal antiferromagnetic-ferromagnetic (AFM-FM) phase transition in FeRh, known for many decades, remains a topic of controversial discussions. The selection of the magnetic degrees of freedom as well as the treatment of the magnetic excited states differ strongly in recent models by different authors. We report a density functional theory (DFT) investigation of FeRh. For the study of excited states, DFT calculations with constraints imposed on the directions and values of the atomic moments are employed. We show that the formation of the Rh moment as a consequence of the AFM-FM phase transition cannot be described within the Stoner picture. Instead, an implicit spin splitting of the Rh states takes place in the AFM phase, resulting in the intra-atomic spin polarization of the Rh atoms. This property is a consequence of the strong hybridization between Rh and Fe states. The Fe-Rh hybridization is an important factor in the physics of FeRh. We demonstrate that the ferromagnetic Fe-Rh exchange interaction is robust with respect to the crystal volume variation, whereas the antiferromagnetic Fe-Fe exchange interaction is strongly volume dependent. These different volume dependencies of the competing exchange interactions lead to their strong compensation at certain crystal volume. We perform Monte Carlo simulations and show that the calculated thermodynamics depends on the way the magnetic degrees of freedom are selected. We argue that the excited states resulting from the variation of the value of the Rh moment treated as degree of freedom are important for both the equilibrium thermodynamics of FeRh and the femtomagnetic phenomena in this system. We also study the spin mixing caused by spin-orbit coupling. The obtained value of the Elliott-Yafet spin-mixing parameter is comparable with earlier calculations for the ferromagnetic 3d metals. We draw the conclusion that the Elliott-Yafet mechanism of the angular-momentum transfer between electrons and lattice plays an important role in the femtomagnetic properties of FeRh.

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Spin-Flip Processes and Ultrafast Magnetization Dynamics in Co: Unifying the Microscopic and Macroscopic View of Femtosecond Magnetism

Cited by 158 publications

References 19 publications

Probing the timescale of the exchange interaction in a ferromagnetic alloy

Probing the timescale of the exchange interaction in a ferromagnetic alloy

Helicity and field dependent magnetization dynamics of ferromagnetic Co/Pt multilayers

Magnetic excitations and femtomagnetism of FeRh: A first-principles study

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