Microwave assisted magnetization switching in Co/Pt multilayer

Abstract

In this study, we have experimentally investigated the microwave assisted magnetization by switching (MAS) on the microstructured Co/Pt multilayer. The sample exhibits the typical magnetization curve peculiar to perpendicular anisotropy films, that is, a steep reversal initiated by nucleation of a reversed domain followed by its subsequent gradual expansion by the domain wall displacement. By applying microwaves with the frequency of GHz order, the nucleation field Hn is significantly reduced at three frequencies. Taking into account the effective anisotropy field of our sample, the first dip of Hn at the lowest frequency probably corresponds to the Kittel mode excitation, and the other two dips at higher frequencies correspond to unidentified excitation modes other than the Kittel mode. Among them, the last dip of Hn at the highest frequency reaches about 1/3 of that without microwave application. These results suggest the existence of more effective excitation modes for MAS than the Kittel mode.

Frequency dependence of critical switching asteroid of CoCrPt–SiO2 granular film under 50-ns microwave impulse

“…[2][3][4][5][6][7][8][9][10][11] Microwave-assisted magnetization reversal (MAMR) has been widely investigated for application to perpendicular magnetic writing in hard disk drives. [12][13][14][15][16] Very recently, a frequency-dependent reduction in the switching field of the magnetization was experimentally reported for CoCrPt-SiO 2 granular films with perpendicular anisotropy. 17,18 Granular films have well-controlled microstructures consisting of small decoupled grains several nanometers in diameter.…”

Microwave-Assisted Magnetization Reversal for Granular Media by a Resonant Cavity Method

“…In MAMR, dc external field and assisting microwave which is generated using a spin torque oscillator, are applied in oblique and perpendicular direction to the disk normal [2]. The general principle of MAMR is verified by a frequency-sweep coplanar waveguide system under perpendicular dc external field [3], [4]. However, in the above-mentioned system, the dynamic behavior of magnetization is assumed to be affected by spatial distribution of microwave intensity caused by form and size of the waveguide, and it is difficult to obtain sufficient signal intensity owing to sample size limitation.…”

Switching Behaviors and its Dynamics of aCo/PtNanodot Under the Assistance of rf Fields

“…Microwave assisted switching (MAS) of magnetization is a newly proposed switching technique as one of the promising candidates for future ultrahigh density magnetic recording technology [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16]. In the MAS, the magnetization direction can be controlled through large amplitude magnetization precession excited by application of radio frequency (rf) magnetic fields.…”

“…However, despite the prospective potential of MAS, which can reduce the switching field of a magnetic element as discussed in many simulations [2][3][4] and analytical calculations [5,6] based on the Landau-Lifshitz-Gilbert (LLG) equation, most of the previous experiments on MAS are limited to soft magnetic materials [7][8][9][10] due to the technical difficulty of generating an rf field large enough to realize MAS for a perpendicular nanomagnet. Recently, few MAS experiments on perpendicular magnetic films [11][12][13][14] and nanodots [15] have been reported, but the MAS effect is not so significant due to the modest rf field amplitude.…”