Nonuniformity of a planar polarizer for spin-transfer-induced vortex oscillations at zero field

We discuss a possible mechanism of the spin-transfer-induced oscillations of a vortex in the free layer of spin-valve nanostructures, in which the polarizer layer has a planar magnetization. We demonstrate that if such planar polarizer is essentially nonuniform, steady gyrotropic vortex motion with large amplitude can be excited. The best excitation efficiency is obtained for a circular magnetization distribution in the polarizer. In this configuration, the conditions for the onset of the oscillations depend on the vortex chirality but not on the direction of its core.

[1]  N. Theodoropoulou,et al.  Low frequency magnetization excitations in magnetic nanopillars induced by a dc spin-polarized current , 2009 .

[2]  B. A. Ivanov,et al.  Eigenfrequencies of vortex state excitations in magnetic submicron-size disks , 2001 .

[3]  K.Yu. Guslienko.  Low-frequency vortex dynamic susceptibility and relaxation in mesoscopic ferromagnetic dots , 2006 .

[4]  Ivanov Ba,et al.  Excitation of spin dynamics by spin-polarized current in vortex state magnetic disks. , 2007 .

[5]  S. E. Russek,et al.  Low-field current-hysteretic oscillations in spin-transfer nanocontacts , 2007 .

[6]  Young-Sang Yu,et al.  Universal criterion and phase diagram for switching a magnetic vortex core in soft magnetic nanodots. , 2008, Physical review letters.

[7]  A. Fert,et al.  Large microwave generation from current-driven magnetic vortex oscillators in magnetic tunnel junctions. , 2010, Nature communications.

[8]  K. Guslienko,et al.  Electric-current-driven vortex-core reversal in soft magnetic nanodots , 2007 .

[9]  V. Cros,et al.  Phase-locking of magnetic vortices mediated by antivortices. , 2009, Nature nanotechnology.

[10]  J. Slonczewski.  Current-driven excitation of magnetic multilayers , 1996 .

[11]  P Crozat,et al.  Current-driven vortex oscillations in metallic nanocontacts. , 2007, Physical review letters.

[12]  Riccardo Hertel,et al.  Magnetization dynamics in spin torque nano-oscillators: Vortex state versus uniform state , 2009 .

[13]  Huan He,et al.  Spin-torque-driven vortex dynamics in a spin-valve pillar with a perpendicular polarizer , 2007 .

[14]  I. N. Krivorotov,et al.  Magnetic vortex oscillator driven by d.c. spin-polarized current , 2007, cond-mat/0702253.

[15]  Vincent Cros,et al.  Vortex oscillations induced by spin-polarized current in a magnetic nanopillar: Analytical versus micromagnetic calculations , 2009 .

[16]  D. Ralph,et al.  Long-timescale fluctuations in zero-field magnetic vortex oscillations driven by dc spin-polarized current , 2009 .

[17]  Andrew G. Glen,et al.  APPL , 2001 .

[18]  K. Guslienko,et al.  Dynamic origin of vortex core switching in soft magnetic nanodots. , 2007, Physical review letters.

[19]  N. A. Usov,et al.  Magnetization curling in a fine cylindrical particle , 1993 .