具有倾斜极化层的自旋阀结构中磁翻转以及磁振荡模式的微磁模拟
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摘要
基于自由层与钉扎层均为垂直磁各向异性的自旋阀结构,采用微磁学模拟与傅里叶分析相结合的技术,研究了极化层磁矩小角度倾斜情形下自由层磁矩的进动翻转特性.通过沿样品垂直膜面方向同时施加电流与磁场,观察到自由层磁矩垂直膜面方向分量的平均值随磁场的演化翻转曲线中出现了多个凹槽.模拟研究结果表明:在一定的电流范围内,凹槽出现的位置与电流大小无关;而在固定的应用电流下,凹槽出现的位置将会受到样品厚度的影响;在凹槽区域内,非一致进动模式、自旋驻波模式、局域自旋波模式等多种磁振荡模式被激发.通过傅里叶分析,得到了各种磁振荡模式的频谱,频谱中的频率分布体现出了倍频以及间谐波的频率特性.
Materials with perpendicular magnetic anisotropy have been intensively investigated due to their potential applications in the nonvolatile magnetic memory and spin-torque oscillators. Hear in this paper, we report a special interesting spin-transfer-driven magnetic behavior in perpendicularly magnetized(Co/Ni)-based spin-valve nano-pillars due to the reduced symmetry of easy axis in the free layer. The micromagnetic simulations indicate that a dip in the average magnetization curve can take place due to the reduced symmetry such as tilt of the magnetic field as well as the easy axis of the free and polarizer layers. In order to further clarify the physics mechanism of the dip, we carry out a series of new simulation studies. In our simulations, we consider a spin-valve nano-pillar with perpendicular anisotropy free layer and a 3? tilted polarizer layer. A negative perpendicular magnetic field and a positive perpendicular current are both applied simultaneously. In the average magnetization curves as a function of the magnetic field with various currents, three dips are observed. Note that although the spin-transfer torque is essential to the appearance of the dips, the position of the dips is less affected by the current in a certain current range. For three dips, we notice that the values are almost identical at a special magnetic field for different currents. At this special magnetic field, the magnetization oscillation modes in the free layer are similar to each other for different currents. The corresponding frequency spectra show that the amplitude of the main frequency peak decreases with the increasing of current due to the enhanced spin-transfer torque. In addition, the frequency shows a blue-shift with the increasing of applied current. Our simulations show that the main frequency f_1 corresponding to the highest peak is approximately equal to the precession frequency of the local magnetization in the free layer. Several high-order frequency peaks are also observed in the frequency spectrum with f_n = nf_1, where n is an integer. Therefore the periodic oscillation of is a harmonic oscillation. Further simulations indicate that the dip appearance is also affected by the thickness of free layer. The spin-transfer torque effect decreases with the thickness of the free layer increasing. As a consequence, the dips shift to a low magnetic field range with the increase of the thickness. And for larger thickness t = 8.0 nm, no dip appears. This result suggests that the spin-transfer torque is necessary for the dip, rather than the unique effect factor, to occur. In the dip region, the magnetic oscillation modes of the free layer show interesting frequency spectrum characters: harmonic frequency or inter-harmonic frequency.As a consequence, the periodic oscillation of the free layer is accompanied by the harmonic waves.
Materials with perpendicular magnetic anisotropy have been intensively investigated due to their potential applications in the nonvolatile magnetic memory and spin-torque oscillators. Hear in this paper, we report a special interesting spin-transfer-driven magnetic behavior in perpendicularly magnetized(Co/Ni)-based spin-valve nano-pillars due to the reduced symmetry of easy axis in the free layer. The micromagnetic simulations indicate that a dip in the average magnetization curve can take place due to the reduced symmetry such as tilt of the magnetic field as well as the easy axis of the free and polarizer layers. In order to further clarify the physics mechanism of the dip, we carry out a series of new simulation studies. In our simulations, we consider a spin-valve nano-pillar with perpendicular anisotropy free layer and a 3? tilted polarizer layer. A negative perpendicular magnetic field and a positive perpendicular current are both applied simultaneously. In the average magnetization curves
引文
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[2]Meng H,Wang J P 2006 Appl.Phys.Lett.88 172506
[3]Mangin S,Henry Y,Ravelosona D,Katine J A,Fullerton E E 2009 Appl.Phys.Lett.94 012502
[4]Ikeda S,Miura K,Yamamoto H,Mizunuma K,Gan HD,Endo M,Kanai S,Hayakawa J,Matsukura F,Ohno H 2010 Nat.Mater.9 721
[5]Su H C,Lei H Y,Hu J G 2015 Chin.Phys.B 24 097506
[6]Katine J A,Fullerton Eric E 2008 J.Magn.Magn.Mater.320 1217
[7]Silva T J,Rippard W H 2008 J.Magn.Magn.Mater.320 1260
[8]Zhou Y,Zha C L,Bonetti S,Persson J,?kerman J 2008Appl.Phys.Lett.92 262508
[9]Sbiaa R,Law R,Tan Ei-L,Liew T 2009 J.Appl.Phys.105 013910
[10]He P B,Wang R X,Li Z D,Liu Q H,Pan A L,Wang Y G,Zou B S 2010 Eur.Phys.J.B 73 417
[11]Lee O J,Pribiag V S,Braganca P M,Gowtham P G,Ralph D C,Buhrman R A 2009 Appl.Phys.Lett.95012506
[12]Papusoi C,Dela?t B,Rodmacq B,Houssameddine D,Michel J P,Ebels U,Sousa R C,Buda-Prejbeanu L,Dieny B 2009 Appl.Phys.Lett.95 072506
[13]Liu H,Bedau D,Backes D,Katine J A,Langer J,Kent A D 2010 Appl.Phys.Lett.97 242510
[14]Rowlands G E,Rahman T,Katine J A,Langer J,Lyle A,Zhao H,Alzate J G,Kovalev A A,Tserkovnyak Y,Zeng Z M,Jiang H W,Galatsis K,Huai Y M,Khalili Amiri P,Wang K L,Krivorotov I N,Wang J P 2011Appl.Phys.Lett.98 102509
[15]Hou Z W,Zhang Z Z,Zhang J W,Liu Y W 2011 Appl.Phys.Lett.99 222509
[16]Zhang H,Hou Z W,Zhang J W,Zhang Z Z,Liu Y W2012 Appl.Phys.Lett.100 142409
[17]Lin W,Cucchiara J,Berthelot C,Hauet T,Henry Y,Katine J A,Fullerton Eric E,Mangin S 2010 Appl.Phys.Lett.96 252503
[18]Le Gall S,Cucchiara J,Gottwald M,Berthelot C,Lambert C H,Henry Y,Bedau D,Gopman D B,Liu H,Kent A D,Sun J Z,Lin W,Ravelosona D,Katine J A,Fullerton E E,Mangin S 2012 Phys.Rev.B 86 014419
[19]Reckers N,Cucchiara J,Posth O,Hassel C,R?mer FM,Narkowicz R,Gallardo R A,Landeros P,Z?hres H,Mangin S,Katine J A,Fullerton E E,Dumpich G,Meckenstock R,Lindner J,Farle M 2011 Phys.Rev.B 83184427
[20]Thiaville A,Rohart S,JuéE,Cros V,Fert A 2012 Europhys.Lett.100 57002
[21]Ryu K S,Thomas L,Yang S H,Parkin S 2013 Nat.Nanotechnol.8 527
[22]Emori S,Bauer U,Ahn S M,Martinez E,Beach G S D2013 Nat.Mater.12 611
[23]Lin W W,Vernier N,Agnus G,Garcia K,Ocker B,Zhao W,Fullerton E E,Ravelosona D 2016 Nat.Commun.713532
[24]Rippard W H,Deac A M,Pufall M R,Shaw J M,Keller M W,Russek S E,Bauer G E W,Serpico C 2010 Phys.Rev.B 81 014426
[25]Mohseni S M,Sani S R,Persson J,Nguyen T N A,Chung S,Pogoryelov Y,Akerman J 2011 Phys.Status Solidi RRL 5 432
[26]Mohseni S M,Sani S R,Persson J,Nguyen T N A,Chung S,Pogoryelov Y,Muduli P K,Iacocca E,Eklund A,Dumas R K,Bonetti S,Deac A,Hoefer M A,Akerman J2013 Science 339 1295
[27]Xiao D,Tiberkevich V,Liu Y H,Liu Y W,Mohseni SM,Chung S,Ahlberg M,Slavin A N,?kerman J,Zhou Y 2017 Phys.Rev.B 95 024106
[28]Zhang H,Lin W W,Mangin S,Zhang Z Z,Liu Y W2013 Appl.Phys.Lett.102 012411
[29]Vansteenkiste A,Leliaert J,Dvornik M,Helsen M,Garcia-Sanchez F,Waeyenberge B V 2014 AIP Adv.4107133
[30]Slonczewski J C 1999 J.Magn.Magn.Mater.195 L261
[31]Li X,Zhang Z Z,Jin Q Y,Liu Y 2008 Appl.Phys.Lett.92 122502