Development of Spin-Torque Oscillators and High <inline-formula> <tex-math notation="LaTeX">${K}\!_{{u}}$ </tex-math></inline-formula> CoPt Media With Small Grain Size for Microwave-Assisted Magnetic Recording

Abstract

We report the selection of materials and design of spin-torque oscillators (STOs) which are able to operate in an alternative magnetic field (variable frequency) of magnitude ∼8000 Oe, generate large enough in-plane ac magnetic field in the recording media, and have tunable high frequency at low driving current for microwave-assisted magnetic recording (MAMR) based on micromagnetic simulations. The mechanism and integration approaches of STOs with the current recording system to have the least driving current are also presented. This paper also covers the material choice, layer-stack optimization, and process development on Co x Pt 1−x alloy films with extremely high coercivity of more than 1.5 T (K u of about 1.5 × 10 7 erg/cc), well-isolated small grains of size 6-7 nm, for the extension of perpendicular magnetic recording and MAMR.Index Terms-Anisotropy energy, composite reference layer, CoPt, magnetization precession, microwave assisted magnetic recording (MAMR), spin-torque oscillator (STO).

Reduction of magnetic damping and isotropic coercivity and increase of saturation magnetization in Rh-incorporated CoIr system

“…Figures 4(c) and (d) show the simulated effect of Ir replacement with Rh on the STO precession frequency and the AC magnetic field generated by STO without and with the presence of external magnetic field. In performing the simulation, the STO has a simple structure of a perpendicular reference layer of dimensions 40×40×20 nm 3 , a 5 nm Cu spacer, and a negative K u FGL (made of CoIr-Rh) of dimensions 40×40×10 nm 3[22,23]. The simulation parameters for the reference layer are fixed at α=0.1, K u =5×10 6 erg cc −1 and M s =800 emu cc −1 .…”

The Dynamics of Microwave-Assisted Magnetic Recording

“…In some cases, the grain magnetization began to switch as soon as the FGL magnetization changed direction; in other cases, several oscillations of the FGL were necessary. Faster switching of the FGL may be accomplished by tuning the damping constant and K u of the SIL, as noted in [16].…”

Magnetic properties tailored by inserting ultrathin Cr layer in Gd/Ni80Fe20film

“…Considering the large spin-orbital coupling of Tb resulting in the enhancement of α, it will be interesting to introduce Gd with a quenched orbital moment to obtain ultra-low damping [9][10][11] required in many magnonic and spin-orbitronic applications [12,13]. For example, the field generation layer of a spin torque oscillator (STO) needs to have an ultra-low damping (α < 0.01) constant for a high working frequency (more than 20 GHz) at a low spin current in minimizing energy consumption, and therefore, enhancing the STO stability and reliability [14][15][16]. Magnetic thin films with low damping are expected for realizing magnetization switching at low critical current densities in high density spin-transfer torque magnetic random access memories (STT-MARM) [17].…”