Connecting the timescales in picosecond remagnetization experiments

Djordjević, Marija; Münzenberg, Markus

doi:10.1103/physrevb.75.012404

Cited by 62 publications

(80 citation statements)

References 31 publications

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“…One can, for example, mention that during the femtosecond demagnetisation the electron temperature is often raised up to the Curie temperature 22,24 . At this moment, the high frequency THz spinwaves 35,36 including the Stoner excitations 30 contribute. At the same time, the transverse relaxation is related to the homogeneous precessional mode.…”

Section: Introductionmentioning

confidence: 99%

Ultrafast magnetization dynamics rates within the Landau-Lifshitz-Bloch model

2011

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The ultra-fast magnetisation relaxation rates during the laser-induced magnetisation process are analyzed in terms of the Landau-Lifshitz-Bloch (LLB) equation for different values of spin S. The LLB equation is equivalent in the limit S → ∞ to the atomistic Landau-Lifshitz-Gilbert (LLG) Langevin dynamics and for S = 1/2 to the M3TM model [B. Koopmans, et al. Nature Mat. 9 (2010) 259]. Within the LLB model the ultra-fast demagnetisation time (τ M ) and the transverse damping (α ⊥ ) are parameterized by the intrinsic coupling-to-thebath parameter λ, defined by microscopic spin-flip rate. We show that for the phonon-mediated Elliott-Yafet mechanism, λ is proportional to the ratio between the non-equilibrium phonon and electron temperatures. We investigate the influence of the finite spin number and the scattering rate parameter λ on the magnetisation relaxation rates. The relation between the fs demagnetisation rate and the LLG damping, provided by the LLB theory, is checked basing on the available experimental data. A good agreement is obtained for Ni, Co and Gd favoring the idea that the same intrinsic scattering process is acting on the femtosecond and nanosecond timescale.

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Section: Introductionmentioning

confidence: 99%

Ultrafast magnetization dynamics rates within the Landau-Lifshitz-Bloch model

2011

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“…This discovery lead to intense theoretical [2][3][4][5][6][7][8][9] and experimental [10][11][12][13][14][15][16] investigations on the origin of these ultrafast magnetization dynamics, however, the dominant microscopic mechanism is still under debate.…”

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Microscopic model for ultrafast magnetization dynamics of multisublattice magnets

Schellekens

Koopmans

2013

Phys. Rev. B

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“…12 In current devices the switching speeds have reached a point where dynamical effects are becoming very important [12][13][14][15][16] Magnons are created in fast (field driven) as well as ultrafast (laser induced) magnetization reversal processes. [17][18][19][20][21][22][23][24][25][26] The former case is of particular interest for current device applications. It is found that above some threshold magnetic field the uniform precessional mode, i.e., the k = 0 magnons decay into nonuniform magnons (k = 0), i.e., the Zeeman energy stays in the magnetic subsystem and scatters between magnon modes.…”

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confidence: 99%

“…[17][18][19][20] However, in ultrafast magnetization reversal the high-energy electrons generated by the laser field decay into the lower-energy magnon excitations. [22][23][24] In both cases spin-orbit coupling (SOC) is responsible for the transfer of the angular momentum to the lattice through different scattering mechanisms such as magnon-magnon, magnon-phonon, magnon-impurity scattering, and so on, where each process has a different relaxation time.27,28 The Landau-Lifshitz-Gilbert (LLG) equation with a phenomenological damping constant α is commonly employed to describe magnetization dynamics of small-angle precessional switching. 29 However, recent studies have shown that in the case of large-angle (fast) switching, in which the magnons are created, the LLG equation should be extended in several aspects, 30,31 in particular, a k-dependent damping constant α k has been proposed, 32,33 which allows shortwavelength magnons to relax faster than those with k → 0.…”

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Strong magnon softening in tetragonal FeCo compounds

2013

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Magnons play an important role in fast precessional magnetization reversal processes serving as a heat bath for dissipation of the Zeeman energy and thus being responsible for the relaxation of magnetization. Employing ab initio many-body perturbation theory we studied the magnon spectra of the tetragonal FeCo compounds considering three different experimental c/a ratios, c/a = 1.13, 1.18, and 1.24 corresponding to FeCo grown on Pd, Ir, and Rh, respectively. We find that for all three cases the short-wavelength magnons are strongly damped and tetragonal distortion gives rise to a significant magnon softening. The magnon stiffness constant D decreases almost by a factor of 2 from FeCo/Pd to FeCo/Rh. The combination of soft magnons together with the giant magnetic anisotropy energy suggests FeCo/Rh to be a promising material for perpendicular magnetic recording applications. Since the introduction of the first commercial hard disk drive in 1956, the recording density in a hard disk, that is, the amount of information that can be stored per square inch, has increased by more than seven orders of magnitude to meet an ever-growing need.1 This has been achieved by a simple scaling of the dimensions of the bits recorded in storage medium. Due to the superparamagnetic effect, however, the recording density has an upper limit. For longitudinal magnetic recording it is around 200 Gbit per square inch, whereas it is predicted to be much larger for perpendicular recording, up to 1000 Gbit per square inch, though this limit is constantly changing with the discovery of new materials. 2-4The major problem in designing magnetic storage media is to retain the magnetization of the medium over a long period of time despite thermal fluctuations. If the ratio of the thermal energy k B T to the magnetic energy per grain K u V , where V is the grain volume and K u is the uniaxial magnetocrystalline anisotropy energy (MAE), becomes sufficiently large, the thermal fluctuations can reverse the magnetization in a region of the medium, destroying the data stored there. 3,5 In order to further increase the recording density in future recording media, high-K u materials are needed. 6 Additionally, a large saturation magnetization M s is beneficial to reduce the write field, which has to be applied by the writing head. Materials that combine the desired large values of K u and M s are tetragonal near-equiatomic FeCo alloys. The large values of K u and M s in these alloys were first predicted by first-principles calculations 7 and then confirmed by experiments. [8][9][10][11] In particular, Yildiz et al.11 achieved a strong perpendicular magnetic anisotropy (PMA) in tetragonal FeCo alloys epitaxially grown on Pd (c/a = 1.13), Ir (c/a = 1.18), and Rh (c/a = 1.24) substrates. The authors found that the PMA is very sensitive to the tetragonal distortion and increases with increasing c/a ratio, which allows to tune the PMA by growing the alloys on different substrates.Besides large K u and M s values, another very important issue in magnetic recor...

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Connecting the timescales in picosecond remagnetization experiments

Cited by 62 publications

References 31 publications

Ultrafast magnetization dynamics rates within the Landau-Lifshitz-Bloch model

Ultrafast magnetization dynamics rates within the Landau-Lifshitz-Bloch model

Microscopic model for ultrafast magnetization dynamics of multisublattice magnets

Strong magnon softening in tetragonal FeCo compounds

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