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The spin-torque oscillator, which can generate an AC voltage oscillation with the same frequency, have attracted considerable attention due to its potential applications in the frequency-tunable transmitters and receivers for wireless communication and the recording heads of high-density hard disk drives. However, from the energy-balance equation's point of view, in the absence of in-plane shape anisotropy of spin torque oscillator, the energy supplied by the spin torque is always larger than the energy dissipation due to the Gilbert damping, thus, a finite magnetic field applied perpendicular to the plane is required for a steady-state precession. This feature has limited its potential applications. In this paper, the influence of the intrinsic in-plane shape anisotropy on the magnetization dynamics of spin torque oscillator consisting of an in-plane polarizer and an out-of-plane free layer is studied numerically in terms of the Landau-Lifshitz-Gilbert-Slonczewski equation. It is demonstrated that the additional in-plane shape anisotropy plays a significant role in the energy balance between the energy accumulation due to the spin torque and the energy dissipation due to Gilbert damping, which can stabilize a steady-state precession. Therefore, a stable self-oscillation in the absence of the applied magnetic field can be excited by introducing additional in-plane shape anisotropy. In particular, a relatively large current region with zero-field self-oscillation, in which the corresponding microwave frequency is increased while the threshold current still maintains an almost constant value, can be obtained by introducing a relatively large intrinsic in-plane shape anisotropy. Our results suggest that a tunable spin transfer oscillator without an applied magnetic field can be realized by adjusting the intrinsic in-plane shape anisotropy, and it may be a promising configuration in the future wireless communications.
[1] Slonczewski J C 1996 J. Magn. Magn. Mater. 159 L1
[2] Berger L 1996 Phys. Rev. B 54 9353
[3] Kiselev S I, Sankey J C, Krivorotov I N, Emley N C, Schoelkopf R J, Buhrman R A, Ralph D C 2003 Nature 425 380
[4] Rippard W H, Pufall M R, Kaka S, Sliva T J, Russek S E, Katine J A 2005 Phys. Rev. Lett. 95 067203
[5] Qiu Y C, Zhang Z Z, Jin Q Y, Liu Y W 2009 Appl. Phys. Lett. 95 052507
[6] Jin W, Wan Z M, Liu Y W 2011 Acta Phys. Sin. 60 017502(in Chinese) [金伟, 万振茂, 刘要稳 2011 60 017502]
[7] Jin W, Liu Y W 2010 Chin. Phys. B 19 037001
[8] Li Z D, He P B, Liu W M 2014 Chin. Phys. B 23 117502
[9] Houssameddine D, Florez S H, Katine J A 2008 Appl. Phys. Lett. 93 022505
[10] Bonetti S, Muduli P, Mancoff F, J. Akernan 2009 Appl. Phys. Lett. 94 102507
[11] Zeng Z M, Amiri P K, Krivorotov I N, Zhao H, Finocchio G, Wang J P, Katine J A, Huai Y, Langer J, Galatsis K, Wang K L, Jiang H 2012 ACS Nano. 6 6115
[12] Huang H B, Ma X Q, Zhao C P, Liu Z H, Chen L Q 2015 J. Magn. Magn. Mater. 373 10
[13] Fang B, Zeng Z M 2014 Chin. Sei. Bull 59 1804 (in Chinese) [方彬, 曾中明 2014 科学通报 59 1804]
[14] Choi H S, Kang S Y, Cho S J, Oh I Y, Shin M, Park H, Jang C, Min B C 2014 Sci. Rep. 4 5486
[15] Braganca P M, Gurney B A, Wilson B A, Katine J A, Maat S, Childress J R 2010 Nanotechnology 21 235202
[16] Kudo K, Nagasawa T, Mizushima K, Suto H, Sato R 2010 Appl. Phys. Express 3 043002
[17] Liu H F, Syed S A, Han X F 2014 Chin. Phys. B 23 077501
[18] Kubota H, Ishibashi S, Nozaki T, Nozaki T, Fukushima A, Yakushiji K, Ando K, Suzuki Y, Yuasa S 2012 J. Appl. Phys. 111 07C723
[19] Kubota H, Yakushiji K, Fukushima A, Tamaru S, Konoto M, Nozaki T, Ishibashi S, Saruya T, Yakata S, Taniguchi T, Arai H, Imamura H 2013 Appl. Phys. Express 6 103003
[20] Zeng Z M, Finocchio G, Zhang B, Amiri P K, Katine J A, Krivorotov I N, Huai Y, Langer J, Azzerboni B, Wang K L, Jiang H 2013 Sci. Rep. 3 1426
[21] Tamaru S, Kubota H, Yakushiji K, Nozaki T, Konoto M, Fukushima A, Imamura H, Taniguchi T, Arai H, Yamji T, Yuasa S 2014 Appl. Phys. Express 7 063005
[22] Taniguchi T, Arai H, Tsunegi S, Tamaru S, Kubota H, Imamura H 2013 Appl. Phys. Express 6 123003
[23] Fowley C, Sluka V, Bernert K, Lindner J, Fassbender J, Rippard W H, Pufall M R, Russek S E, Deac A M 2014 Appl. Phys. Express 7 043001
[24] Slonczewski J C 2005 Phys. Rev. B 71 024411
[25] Slonczewski J C, Sun J Z 2007 J. Magn. Magn. Mater. 310 169
[26] Coey J M D 2010 Magnetism and Magnetic Materials (Cambridge: Cambridge University Press) p168
[27] Taniguchi T 2014 Appl. Phys. Express 7 053004
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[1] Slonczewski J C 1996 J. Magn. Magn. Mater. 159 L1
[2] Berger L 1996 Phys. Rev. B 54 9353
[3] Kiselev S I, Sankey J C, Krivorotov I N, Emley N C, Schoelkopf R J, Buhrman R A, Ralph D C 2003 Nature 425 380
[4] Rippard W H, Pufall M R, Kaka S, Sliva T J, Russek S E, Katine J A 2005 Phys. Rev. Lett. 95 067203
[5] Qiu Y C, Zhang Z Z, Jin Q Y, Liu Y W 2009 Appl. Phys. Lett. 95 052507
[6] Jin W, Wan Z M, Liu Y W 2011 Acta Phys. Sin. 60 017502(in Chinese) [金伟, 万振茂, 刘要稳 2011 60 017502]
[7] Jin W, Liu Y W 2010 Chin. Phys. B 19 037001
[8] Li Z D, He P B, Liu W M 2014 Chin. Phys. B 23 117502
[9] Houssameddine D, Florez S H, Katine J A 2008 Appl. Phys. Lett. 93 022505
[10] Bonetti S, Muduli P, Mancoff F, J. Akernan 2009 Appl. Phys. Lett. 94 102507
[11] Zeng Z M, Amiri P K, Krivorotov I N, Zhao H, Finocchio G, Wang J P, Katine J A, Huai Y, Langer J, Galatsis K, Wang K L, Jiang H 2012 ACS Nano. 6 6115
[12] Huang H B, Ma X Q, Zhao C P, Liu Z H, Chen L Q 2015 J. Magn. Magn. Mater. 373 10
[13] Fang B, Zeng Z M 2014 Chin. Sei. Bull 59 1804 (in Chinese) [方彬, 曾中明 2014 科学通报 59 1804]
[14] Choi H S, Kang S Y, Cho S J, Oh I Y, Shin M, Park H, Jang C, Min B C 2014 Sci. Rep. 4 5486
[15] Braganca P M, Gurney B A, Wilson B A, Katine J A, Maat S, Childress J R 2010 Nanotechnology 21 235202
[16] Kudo K, Nagasawa T, Mizushima K, Suto H, Sato R 2010 Appl. Phys. Express 3 043002
[17] Liu H F, Syed S A, Han X F 2014 Chin. Phys. B 23 077501
[18] Kubota H, Ishibashi S, Nozaki T, Nozaki T, Fukushima A, Yakushiji K, Ando K, Suzuki Y, Yuasa S 2012 J. Appl. Phys. 111 07C723
[19] Kubota H, Yakushiji K, Fukushima A, Tamaru S, Konoto M, Nozaki T, Ishibashi S, Saruya T, Yakata S, Taniguchi T, Arai H, Imamura H 2013 Appl. Phys. Express 6 103003
[20] Zeng Z M, Finocchio G, Zhang B, Amiri P K, Katine J A, Krivorotov I N, Huai Y, Langer J, Azzerboni B, Wang K L, Jiang H 2013 Sci. Rep. 3 1426
[21] Tamaru S, Kubota H, Yakushiji K, Nozaki T, Konoto M, Fukushima A, Imamura H, Taniguchi T, Arai H, Yamji T, Yuasa S 2014 Appl. Phys. Express 7 063005
[22] Taniguchi T, Arai H, Tsunegi S, Tamaru S, Kubota H, Imamura H 2013 Appl. Phys. Express 6 123003
[23] Fowley C, Sluka V, Bernert K, Lindner J, Fassbender J, Rippard W H, Pufall M R, Russek S E, Deac A M 2014 Appl. Phys. Express 7 043001
[24] Slonczewski J C 2005 Phys. Rev. B 71 024411
[25] Slonczewski J C, Sun J Z 2007 J. Magn. Magn. Mater. 310 169
[26] Coey J M D 2010 Magnetism and Magnetic Materials (Cambridge: Cambridge University Press) p168
[27] Taniguchi T 2014 Appl. Phys. Express 7 053004
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