Theory of laser-induced demagnetization at high temperatures

Manchon, Aurélien; Li, Q.; Xu, Lei; Zhang, S.

doi:10.1103/physrevb.85.064408

Cited by 54 publications

(53 citation statements)

References 41 publications

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“…Such a scenario suggests that the spin flip scattering mechanisms leading to demagnetization may be shorter in range than the helix period. It may, however, also play a role that the present experiment was carried out near the ordering temperature and that critical slowing down [45,46] obscures an otherwise faster dynamics. To clarify this issue, further complementary experiments, e.g., at the Ho M 5 edge could provide additional insight.…”

Section: Prl 116 257202 (2016) P H Y S I C a L R E V I E W L E T T Ementioning

confidence: 93%

Itinerant and Localized Magnetization Dynamics in Antiferromagnetic Ho

et al. 2016

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Using femtosecond time-resolved resonant magnetic x-ray diffraction at the Ho L 3 absorption edge, we investigate the demagnetization dynamics in antiferromagnetically ordered metallic Ho after femtosecond optical excitation. Tuning the x-ray energy to the electric dipole (E1, 2p → 5d) or quadrupole (E2, 2p → 4f) transition allows us to selectively and independently study the spin dynamics of the itinerant 5d and localized 4f electronic subsystems via the suppression of the magnetic (2 1 3-τ) satellite peak. We find demagnetization time scales very similar to ferromagnetic 4f systems, suggesting that the loss of magnetic order occurs via a similar spin-flip process in both cases. The simultaneous demagnetization of both subsystems demonstrates strong intra-atomic 4f-5d exchange coupling. In addition, an ultrafast lattice contraction due to the release of magneto-striction leads to a transient shift of the magnetic satellite peak. DOI: 10.1103/PhysRevLett.116.257202 The manipulation of magnetic order by ultrashort light pulses is of fundamental interest in solid state research and promises high technological relevance. Since the discovery of the demagnetization of Ni in <1 ps almost two decades ago [1], the ultrafast magnetization dynamics of ferromagnetic systems has been intensely studied both experimentally and theoretically [2-6]; for a review see Refs. [7,8]. In particular, the phenomenon of ultrafast magnetization reversal recently observed in ferrimagnetic lanthanide transition metal intermetallics [8][9][10][11][12][13] has attracted much attention. In these materials a complex interaction between localized f moments in the rare-earth ions and the itinerant transition metal d electrons is thought to enable the reversal of the magnetic moment on subpicosecond time scales. The interaction leads to several unexpected phenomena such as a transient ferromagnetic state in FeCoGd [10] and ultrafast angular momentum transfer between different volumes within an inhomogeneous ferrimagnetic alloy [12].In the rare-earth metals, the magnetic exchange interaction between the large localized moments of the open 4f shells is mediated by the indirect Ruderman-Kittel-KasuyaYosida (RKKY) interaction via the itinerant 5d6s electrons, leading to a parallel alignment of the two subsystems. Depending on the details of the band structure, this interaction results in a variety of magnetically ordered ground states, ranging from ferromagnetic alignment in Gd and Tb to complex antiferromagnetic (AFM) structures in the heavier rare earths. As optical excitation directly interacts with the valence electrons and not with the localized 4f states, these systems present an ideal case to study the 4f-5d interaction directly in the time domain by separately investigating the dynamics of these two subsystems. While early experiments using x-ray magnetic circular dichroism (XMCD) and the magneto-optical Kerr effect (MOKE) on the ferromagnetic lanthanides Gd and Tb found similar demagnetization time scales of 4f and 5d electrons [14], more...

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Section: Prl 116 257202 (2016) P H Y S I C a L R E V I E W L E T T Ementioning

confidence: 93%

Itinerant and Localized Magnetization Dynamics in Antiferromagnetic Ho

et al. 2016

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“…We adopt the viewpoint that demagnetization is a result of excitation of magnons 15,30,31 and explain the demagnetization of the [Co/Pt] layer by the exchange of thermal energy between electrons, magnons and phonons, see for details of the thermal modelling). At 0.2 ps, the electron temperature, T e , of the [Co/Pt] layer (blue dotted line) sharply increases by DTE90 K due to electronic thermal transport from the Pt layer.…”

Section: Experimentmentioning

confidence: 99%

“…To model the spin current generation, we assume that electron-magnon coupling conserves spin angular momentum 30 . Thus, the spin loss by demagnetization should be converted to spin generation, that is, spin polarization in the electrons, and the spin generation rate is the negative of the demagnetization rate, À dM/dt (see Supplementary Note 5).…”

Section: Experimentmentioning

confidence: 99%

Spin current generated by thermally driven ultrafast demagnetization

Choi

Min

Lee³

et al. 2014

Nat Commun

196

203

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Spin current is the key element for nanoscale spintronic devices. For ultrafast operation of such nano-devices, generation of spin current in picoseconds, a timescale that is difficult to achieve using electrical circuits, is highly desired. Here we show thermally driven ultrafast demagnetization of a perpendicular ferromagnet leads to spin accumulation in a normal metal and spin transfer torque in an in-plane ferromagnet. The data are well described by models of spin generation and transport based on differences and gradients of thermodynamic parameters. The temperature difference between electrons and magnons is the driving force for spin current generation by ultrafast demagnetization. On longer timescales, a few picoseconds following laser excitation, we also observe a small contribution to spin current by a temperature gradient and the spin-dependent Seebeck effect.

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“…13,[37][38][39][40][41][42] In ferrimagnets, there is a large interest on demagnetization rates of each species, following the use of X-ray magnetic circular dichroism 5 to monitor the sub-picosecond dynamics of each sublattice magnetization individually. 4 Thermal effects dominate the magnetization dynamics during the heating produced by the laser.…”

Section: Estimation Of the Temperature Dependent Magnetization Relmentioning

confidence: 99%

Controlling the polarity of the transient ferromagneticlike state in ferrimagnets

et al. 2014

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It was recently observed that the two antiferromagnetically coupled sublattices of a rare earth-transition metal ferrimagnet can temporarily align ferromagnetically during femtosecond laser heating, but always with the transition metal aligning in the rare earth direction. This behavior has been attributed to the slower magnetization dynamics of the rare earth sublattice. The aim of this work was to assess how the difference in the speed of the transition metal and rare earth dynamics affects the formation of the transient ferromagnetic-like state and consequently controls its formation. Our investigation was performed using extensive atomistic spin simulations and analytic micromagnetic theory of ferrimagnets, with analysis of a large area of parameter space such as initial temperature, Gd concentration and laser fluence. Surprisingly, we found that at high temperatures, close to the Curie point, the rare earth dynamics become faster than those of the transition metal. Subsequently we show that the transient state can be formed with the opposite polarity, where the rare earth aligns in the transition metal direction. Our findings shed light on the complex behavior of this class of ferrimagnetic materials and highlight an important feature which must be considered, or even exploited, if these materials are to be used in ultrafast magnetic devices.

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Theory of laser-induced demagnetization at high temperatures

Cited by 54 publications

References 41 publications

Itinerant and Localized Magnetization Dynamics in Antiferromagnetic Ho

Itinerant and Localized Magnetization Dynamics in Antiferromagnetic Ho

Spin current generated by thermally driven ultrafast demagnetization

Controlling the polarity of the transient ferromagneticlike state in ferrimagnets

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