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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 mz 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 mz 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 f1 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 fn=nf1, where n is an integer. Therefore the periodic oscillation of mz 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.
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Keywords:
- micromagnetic simulations /
- spin-transfer torque /
- spin wave mode
[1] Mangin S, Ravelosona D, Katine J A, Carey M J, Terris B D, Fullerton E E 2006 Nature Mater. 5 210
[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 H D, 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 2008 Appl. 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. 95 012506
[12] Papusoi C, Delat 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 2011 Appl. 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 W 2012 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, Rmer F M, Narkowicz R, Gallardo R A, Landeros P, Zhres H, Mangin S, Katine J A, Fullerton E E, Dumpich G, Meckenstock R, Lindner J, Farle M 2011 Phys. Rev. B 83 184427
[20] Thiaville A, Rohart S, Ju E, 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 D 2013 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. 7 13532
[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 J 2013 Science 339 1295
[27] Xiao D, Tiberkevich V, Liu Y H, Liu Y W, Mohseni S M, 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 W 2013 Appl. Phys. Lett. 102 012411
[29] Vansteenkiste A, Leliaert J, Dvornik M, Helsen M, Garcia-Sanchez F, Waeyenberge B V 2014 AIP Adv. 4 107133
[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
-
[1] Mangin S, Ravelosona D, Katine J A, Carey M J, Terris B D, Fullerton E E 2006 Nature Mater. 5 210
[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 H D, 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 2008 Appl. 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. 95 012506
[12] Papusoi C, Delat 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 2011 Appl. 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 W 2012 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, Rmer F M, Narkowicz R, Gallardo R A, Landeros P, Zhres H, Mangin S, Katine J A, Fullerton E E, Dumpich G, Meckenstock R, Lindner J, Farle M 2011 Phys. Rev. B 83 184427
[20] Thiaville A, Rohart S, Ju E, 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 D 2013 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. 7 13532
[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 J 2013 Science 339 1295
[27] Xiao D, Tiberkevich V, Liu Y H, Liu Y W, Mohseni S M, 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 W 2013 Appl. Phys. Lett. 102 012411
[29] Vansteenkiste A, Leliaert J, Dvornik M, Helsen M, Garcia-Sanchez F, Waeyenberge B V 2014 AIP Adv. 4 107133
[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
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