Observation of Precessional Magnetization Dynamics in L10-FePt Thin Films with Different L10 Order Parameter Values

Iihama, Satoshi; Mizukami, Shigemi; Inami, Nobuhito; Hatori, Takashi; Kim, Gukcheon; Naganuma, Hiroshi; Oogane, Mikihiko; Miyazaki, T.; Ando, Yasuo

doi:10.7567/jjap.52.073002

Cited by 25 publications

(18 citation statements)

References 25 publications

(27 reference statements)

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“…We list the damping values and compare the calculated magnetic moments and the experimental data in Table I calculated is in good quantitative agreement with experiment. 3,31 The damping value of FePt 0.02 also agrees with the measurement by Iihama and Ando et al 32 The distinctly larger damping of Pt-based to Pd-based alloys is caused by the stronger SOI strength in Pt (0.5 eV) than Pd (0.15 eV). We verified the damping computation is robust to the TB orbit parameters.…”

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confidence: 88%

Effect of substitutional defects on Kambersky damping in L1 magnetic materials

Victora

2015

Applied Physics Letters

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Kambersky damping, representing the loss of magnetic energy from the electrons to the lattice through the spin orbit interaction, is calculated for L1 0 FePt, FePd, CoPt, and CoPd alloys versus chemical degree of order. When more substitutional defects exist in the alloys, damping is predicted to increase due to the increase of the spin-flip channels allowed by the broken symmetry. It is demonstrated that this corresponds to an enhanced density of states (DOS) at the Fermi level, owing to the rounding of the DOS with loss of long-range order. Both the damping and the DOS of the Co-based alloy are found to be less affected by the disorder. Pd-based alloys are predicted to have lower damping than Pt-based alloys, making them more suitable for high density spintronic applications. V C 2015 AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4909510]In both advanced spintronic and magnetic recording applications, high magnetic anisotropy materials play a key role because they are stable against thermal fluctuations, even at the nano-scale. 1 The L1 0 -ordered alloys, such as FePt, CoPt, FePd, and CoPd, exhibit a very large uniaxial magnetic anisotropy energy above 1 Â 10 7 erg/cm 3 and a moderate saturation magnetization Ms ¼ 1140 emu/cm 3 (for FePt and FePd) or 800 emu/cm 3 (for CoPt and CoPd) in bulk. 2,3 In magnetic recording, the Gilbert damping constant a affects the writing speed because it reflects energy lost in the switching dynamics. In magnetic field controlled switching processes, 4 large a is preferred to increase the writing speed. Conversely, microwave 5 or spin-transfer-torque switching 6 require the minimization of a to increase energy efficiency.It is imperative to gain insight into the many sources of a, including magnon-magnon interaction mediated by defects, 7 four-magnon scattering, 8 and magnon-electron interaction. 9 The most intrinsic source is Kambersky damping, 10 representing magnetic energy lost to the lattice through the spin-orbit interaction (SOI). This mechanism is mostly explored in traditional bulk 11-14 and thin film 15 transition materials: Fe, Co, and Ni. Calculation of a has been approached in torque-correlation theory, 10 linear response theory, 16 and scattering theory, 17 respectively. The Kambersky mechanism is especially prominent in the listed L1 0 ordered alloys as high crystalline anisotropy implies strong SOI. Also, Pt has obviously larger SOI strength n of 0.5 eV (Ref. 18) than the 3d transition metals such as Fe and Co. Studies show that high perpendicular anisotropy magnets including Pt possess large a, like Co/Pt multilayers, 15,19 ultrathin CoFeB/Pt (Ref. 20), and Pt/Co films. 21 However, the reported experimental damping values in L1 0 alloys differ among investigators. [22][23][24][25] Besides, the spin-flip scattering due to the random arrangement of atoms is infrequently investigated although the magnetic materials fabricated are mostly disordered systems. Sakuma's calculation 26 of a in L1 0 FePt assumes cubic symmetry, which may account for the apparent discrep...

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confidence: 88%

Effect of substitutional defects on Kambersky damping in L1 magnetic materials

Victora

2015

Applied Physics Letters

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“…The difference between the experimental data and calculated data diverged with increasing θ H , and the reason for this remaining unclear at present. This behavior was also observed for the L1 0 -FePt film 7) . Furthermore, we tried to explain the dependence of 1/τ on θ H by using the two-magnon scattering model 32) since 1/τ enhancement at θ > 45 • with this model has been reported for polycrystalline Co film 30,31) .…”

Section: (B) and 3(c)supporting

confidence: 73%

“…Recently, fast magnetization dynamics for films with large PMA such as L1 0 -FePt and L1 0 -FePdPt alloys, and Co/Pt and Co/Pd multilayers have been intensively investigated [5][6][7][8][9][10][11][12][13] . The reported α values for these materials have been 0.06−0.2 [5][6][7] for L1 0 -FePt alloy, 0.05−0.15 10,11) for Co/Pt multilayers, and 0.04−0.2 12,13) for Co/Pd multilayers, which are much larger than those for Fe and Co. One reason for the large α is the presence of heavy elements Pt and Pd because α originates from their spin-orbit interactions 9,[14][15][16] . Despite many reports on other films with PMA [17][18][19][20][21][22][23] , α values for L1 0 -FePd are unclear at present.…”

Section: Introductionmentioning

confidence: 99%

Magnetization Dynamics and Damping for L10-FePd Thin Films with Perpendicular Magnetic Anisotropy

et al. 2015

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Magnetization dynamics and damping for FePd films were investigated using the all-optical time-resolved magneto-optical Kerr effect. We deposited 16-nm-thick FePd thin films on a single crystal MgO(001) substrate. Both in-plane magnetic anisotropy and perpendicular magnetic anisotropy (PMA) FePd films were fabricated using the magnetron sputtering method at various substrate temperatures T s . The dependencies of magnetization dynamics on the external magnetic field angle at fixed external magnetic field strengths were analyzed. The effective damping constant, α eff , for FePd films with PMA exhibited anisotropy, whereas the α eff for FePd with in-plane magnetic anisotropy did not depend significantly on the field angle. A uniaxial crystalline magnetic anisotropy constant, K u1 , of 11 Merg/cm 3 and a minimum for α eff of 0.007 were observed for film prepared at T s = 200 • C. This α eff value was much smaller than that for other Fe-and Co-based materials with large PMA such as L1 0 -FePt alloy, Co/Pt(Pd) multilayers.

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“…It is difficult to determine the electron-phonon scattering rate sufficiently accurate from experiments, while the electron-impurity scattering can be controlled by either doping or artificial disorder. However, no direct experiments have been reported to verify quantitatively the relationship between α 0 and 1/τ e through impurity scattering despite many attempts [33,[44][45][46][47]. The challenge lies in the fact that α 0 also depends on other leading parameters, such as magnetization M S [33], SOI [44], lattice distortion [47], and D(E F ) [40], which may vary significantly when the impurity concentration is modulated.…”

Section: Introductionmentioning

confidence: 99%

“…It is difficult to determine the electron-phonon scattering rate sufficiently accurate from experiments, while the electron-impurity scattering can be controlled by either doping or artificial disorder. However, no direct experiments have been reported to verify quantitatively the relationship between α 0 and 1/τ e through impurity scattering despite many attempts [33,[44][45][46][47] may vary significantly when the impurity concentration is modulated. It is difficult to quantitatively investigate the impact of 1/τ e on α 0 in those material systems.…”

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confidence: 99%

Role of antisite disorder on intrinsic Gilbert damping inL10FePt films

et al. 2015

Phys. Rev. B

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The impact of anti-site disorder x on the intrinsic Gilbert damping α 0 in well-ordered 1 FePt films is investigated by time-resolved magneto-optical Kerr effect. The variation of x mainly affects the electron scattering rate 1/τ e , while other leading parameters remain unchanged. The experimentally observed linear dependence of α 0 on 1/τ e indicates that spin relaxation is through electron interband transitions, as predicted by spin-orbit coupling torque correlation model. Measurements at low temperature show that α 0 remains unchanged with temperature even for FePt with very high chemical order, indicating that electron-phonon scattering is negligible. Moreover, as x decreases the perpendicular magnetic anisotropy increases and the Landau g factor exhibits a negative shift due to an increase in orbital momentum anisotropy. Our results will facilitate the design and exploration of new magnetic alloys with large magnetic anisotropy and desirable damping properties.PACS numbers: 75.78. Jp, 75.70.Tj, 75.50.Vv, 75.30.Gw + e-mail: hbzhao@fudan.edu.cn *e-mail: gxluep@wm.edu.[2] IntroductionUltrafast magnetization precessional switching in ferromagnets utilizing magnetic field pulses, spin polarized currents, and ultrafast laser pulses [1][2][3][4][5][6] is currently a popular topic due to its importance in magnetic information storage and spintronic applications. The uniform magnetization precession can be well modeled with Landau-Lifshitz-GilbertSlonczewski (LLGS) equation [7][8][9], where the Slonczewski torque term denotes the spin transfer torques (STTs), and the Gilbert damping parameter α determines the spin relaxation time [10] and is crucial for device performance [11][12][13][14]. The extrinsic Gilbert damping is due to nonlocal spin relaxation, such as spin pumping and magnon-magnon scattering, which can be tuned by artificial substrates, specially designed buffer and coverage layers [15][16][17][18][19][20][21], while the intrinsic Gilbert damping parameter α 0 is thought to arise from spin-orbit interaction (SOI) [22][23][24][25][26][27][28][29][30], and recently its quadratic dependence on SOI is demonstrated experimentally in FePtPd alloys [31].The α 0 describes the energy flow rate from spin to electronic orbital and phonon degrees of freedom through electron scattering, and has been studied in various theoretical models [22][23][24][25][26][27][28][29][30]. The breathing Fermi surface model [22] and torque-correlation model [23] based on first principle band structure calculations qualitatively match α 0 in soft magnetic alloys such as Fe, . Moreover, contributions to α 0 can be categorized based on intraband and interband transitions [23,26]. The damping rate from intraband transitions scales linearly with the electron relaxation time τ e and exhibits conductivity-like behavior. In contrast, the damping rate from the interband transition is proportional to the electron scattering rate 1/τ e , and consequently exhibits resistivity-like behavior. Therefore, the transition from conductivity-like to re...

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Observation of Precessional Magnetization Dynamics in L1₀-FePt Thin Films with Different L1₀ Order Parameter Values

Cited by 25 publications

References 25 publications

Effect of substitutional defects on Kambersky damping in L1 magnetic materials

Effect of substitutional defects on Kambersky damping in L1 magnetic materials

Magnetization Dynamics and Damping for <i>L</i>1<sub>0</sub>-FePd Thin Films with Perpendicular Magnetic Anisotropy

Role of antisite disorder on intrinsic Gilbert damping inL10FePt films

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