Power and linewidth of propagating and localized modes in nanocontact spin-torque oscillators

Abstract

Integrated power and linewidth of a propagating and a self-localized spin wave modes excited by spin-polarized current in an obliquely magnetized magnetic nanocontact are studied experimentally as functions of the angle θe between the external bias magnetic field and the nanocontact plane. It is found that the power of the propagating mode monotonically increases with θe, while the power of the self-localized mode has a broad maximum near θe = 40 deg, and exponentially vanishes near the critical angle θe = 58 deg, at which the localized mode disappears. The linewidth of the propagating mode in the interval of angles 58 < θe < 90 deg , where only this mode is excited, is adequtely described by the existing theory, while in the angular interval where both modes can exist the observed linewidth of both modes is substantially broadened due to the telegraph switching between the modes. Numetical simulations and an approximate analytical model give good semiquantitative description of the observed results.

Magnetic droplet solitons in orthogonal spin valves

“…For example, in easyplane material based devices such as STNOs with Permalloy free layers, in addition to vortices [26][27][28], both propa-gating spin waves [29][30][31][32][33][34][35][36] and self-localized spin wave bullet solitons [31][32][33]37] can be generated experimentally.…”

Generation linewidth of mode-hopping spin torque oscillators

“…However, recent experiments have shown multi-mode generation in a large variety of geometries [28][29][30], revealing evidence of mode-hopping [31][32][33], periodic mode transitions [5,7], and even coexistence [8]. Furthermore, such a multi-mode generation leads to broader linewidths ascribed to the reduction of the magnetization dynamics coherence.…”

“…STT describes the momentum transfer from spin-polarized electrons to a local magnetization and therefore provides a direct coupling between dc charge currents and magnetization dynamics. Depending on external conditions, a rich variety of physical phenomena with technologically interesting outcomes are possible, including different modes of spin wave generation [3][4][5][6][7][8], vortex gyration [9][10][11][12], and the nucleation and manipulation of magnetic droplet solitons [13][14][15][16]. Regardless of the particular magnetization dynamics, devices where a stable oscillatory state can be achieved are generally referred to as spin torque oscillators [17,18] (STOs), and are typically composed of two ferromagnetic layers decoupled by a non-magnetic spacer (although recent studies also report on STOs based on single ferromagnet layers [19]).…”

Mutually synchronized bottom-up multi-nanocontact spin–torque oscillators

“…Each nanocontact can sustain several tens of mA current, which gets spin polarized and transfers angular momentum between the two magnetic layers via the so-called spin-transfer torque (STT) effect [35][36][37] . At sufficiently high current densities (B10 8 A cm À 2 ), STT can sustain continuous precession of the local magnetization underneath the nanocontact and also inject high amplitudes of either localized or propagating spin waves (SWs) into the free layer 20,22,23,[38][39][40][41][42][43] .…”