Role of antisite disorder on intrinsic Gilbert damping inL10FePt films

Abstract

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...

Gilbert damping in binary magnetic multilayers

“…This can be related to the fact that the Gilbert damping in such Fe/Pt systems has been shown experimentally [27] to be strongly enhanced by intermixing at FM/NM interfaces which is not accounted for in the present calculations for Co/NM superlattices. Indeed, our theoretical values of α in the L1 0 Co/Pt films with ∼ 0.1 eV are close to α ≈ 0.05 found experimentally in the L1 0 FePt films with low antisite disorder [27].…”

“…Measurements of the damping constant α in [FM/NM] N binary superlattices have been reported by different experimental groups [22,23,[25][26][27][42][43][44][45][46][47][48][49][50][51][52]. The presence of NM layers in magnetic binary superlattices results in larger magnetic damping in comparison with the corresponding bulk ferromagnetic metals.…”

“…Such multilayers can exhibit oscillatory interlayer exchange coupling [5][6][7][10][11][12] and giant magnetorestistance [5,10,13,14] as well as large perpendicular magnetic anisotropy (PMA) due to the magnetocrystalline anisotropy terms arising from the multiple FM/NM interfaces. In particular, large PMA is found in Fe/Pt, Co/Pd, and Co/Pt multilayers [15][16][17][18][19][20][21][22][23], including L1 0 superlattices [24][25][26][27]. Magnetic multilayers with out-of-plane magnetization are essential ingredients in spintronic applications, in particular, they turn out to be suitable in spin-transfer torque devices like magnetic random access memory (MRAM) [28][29][30][31].…”

The effect of growth sequence on magnetization damping in Ta/CoFeB/MgO structures

“…The second term corresponds to the damped magnetization precession; B, , , and are amplitude, relaxation time, frequency, and the initial phase of magnetization precession, respectively [17,27]. From a fit to the Kerr rotation spectra, we extracted the values of the and .…”

“…The femtosecond pulse train generated by a Ti: sapphire laser with a pulse duration of 50 fs and a repetition rate of 1 kHz was divided into pump and probe pulse beam. The pump pulse beam with a fluence of 3.54 mJ was focused to a spot of ~600 m in diameter on the sample to excite the magnetization precession, while the probe pulse beam with a fluence of 0.06 mJ was focused to a spot size of ~200 m in diameter and overlapped with the pump laser spot on the sample surface [16][17][18][19][20]. The Kerr rotation of reflected probe pulse beam was detected by a balanced detector.…”