Kerr microscopy studies of microwave assisted switching

Abstract

We study microwave assisted magnetization reversal of elliptical Ni81Fe19 thin film elements employing Kerr microscopy. A microwave field is applied along the short axis of the element and orthogonally to a quasistatic magnetic field, which is parallel to the long axis of the element. The reversal process is characterized by the formation of a complex multidomain structure. We demonstrate that the reversal process in total is compressed by applying a sufficiently high microwave field, which assists to overcome the effective energy barrier of the domain nucleation, and thus reduces the coercive field.

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.…”

Observation of microwave-assisted magnetization reversal in Fe65Co35 thin films through ferromagnetic resonance measurements

“…Several other experiments confirmed the MAMR effect. Specifically, Grollier et al 5 demonstrated microwave-assisted reversal in cobalt strips by means of anisotropic magnetoresistance measurements; Nembach et al 6 and Pimentel et al 7 10,11 reported the observation of MAMR effects in Permalloy layers in magnetic tunnel junctions.…”

“…6,7 The new approach presented here, however, allows the direct study of MAMR effects in bare samples, as explained below. Note that in Refs.…”

“…The presumed underlying mechanism for this reduction is that the microwave field excites largeangle magnetization precessions, and the large-angle precessions lead to a reduction in the energy barrier for domain nucleation and hence a reduction in the switching field. 6,7 In conclusion, a new approach for MAMR measurements on bare samples was developed. This approach uses one and the same microstrip line to deliver microwaves to and measure the FMR response of the sample.…”

Chirped-microwave assisted magnetization reversal

“…Following the work by Thirion et al, the MAMR response was confirmed in a number of different types of magnetic elements. These include single-domain elements, such as submicron cobalt particles 2 and micron-sized Permalloy film elements, 3 and multidomain materials, such as cobalt strips, 4 Permalloy thin films, 5,6 submicron-wide Permalloy wires, 7 and Permalloy layers in magnetic tunnel junctions. 8,9 In addition to the experimental work summarized above, the numerical simulations of MAMR processes have also been carried out on the basis of the torque equation of motion with damping.…”