High Speed Switching and Rotational Dynamics in Small Magnetic Thin Film Devices

Abstract

Abstract. The intent of this chapter is to review high-frequency magnetic device measurements and modeling work at NIST which is being conducted to support the development of high-speed read sensors, magnetic random access memory, and magnetoelectronic applications (such as isolators and microwaves components). The chapter will concentrate on magnetoresistive devices, those devices whose resistance is a function of the magnetic state of the device, which can in turn be controlled by a magnetic field. The low-frequency characteristics of magnetoresistive devices will be reviewed. Simulated high-frequency device dynamics, using single-domain and micromagnetic models, will be discussed. Next, high-speed measurements of magnetization rotation and switching in micrometer-size devices will be presented. The effects of thermal fluctuations and disorder on device dynamics will be examined, and high-frequency magnetic noise data will be presented. Finally, the need to understand and control high-frequency magnetic damping will be discussed, and a method for engineering high-frequency magnetization damping using rare-earth doping will be presented.

Manipulation of magnetic particles by patterned arrays of magnetic spin-valve traps

“…The details of the microfabrication process for generating the platform can be found in previous work [14,15]. We made a modification to the magnetic structures in this previous by replacing lowcoercivity permalloy traps with permanent magnet spinvalve traps [16][17][18] on a 200 nm thick silicon nitride support membrane. The spin valves have a six layer composition comprised of 5 nm Ta/15 nm Ni 80 Fe 20 /5 nm Co/10 nm Cu/ 5 nm Co/15 nm Ni 80 Fe 20 /5 nm IrMn/5 nm Ta.…”

Current induced magnetization switching in Co/Cu/Ni-Fe nanopillar with orange peel coupling

“…30 When the nonmagnetic spacer layer has the correlated waviness interface, and the magnetization of the two ferromagnetic layers are parallel to each other, magnetostatic charges of opposite sign appear symmetrically on the opposing interfaces. The dipole interaction between these opposing charges gives rise to a ferromagnetic coupling between the magnetization of the two ferromagnetic layers known as orange peel coupling 31 referred so because of the dimpled texture of an orange 32 and produce a coupling field normal to the magnetization of the easy axis. Hence, it is expected to contribute to the reduction in switching time.…”

Magnetization dynamics in microscopic spin-valve elements: Shortcomings of the macrospin picture

“…Finally, the dynamic magnetization reversal in the free layer may affect the magnetization configuration in the hard layer. 20 The free layer in spin valves was found to show an increased damping coefficient, 18,21 which was attributed to a nonlocal spin pumping model. 22,23 A competing damping process, however, is given by the local excitation of additional shortwavelength and high-frequency spin wave modes.…”

“…22,23 A competing damping process, however, is given by the local excitation of additional shortwavelength and high-frequency spin wave modes. 24,25 In general, a local variation of the precessional magnetization motion will lead to unwanted magnetically induced noise in the response of a spin valve 21 or any other fast-switching magnetic structure. 29 Therefore, the understanding of the local magnetization dynamics in complex layer stacks is extremely important, as the dynamics may be determined in a complicated way by the various magnetic coupling effects in a thin film structure.…”

“…25 The control of ␣ holds the key for optimized magnetic switching procedures. 21 The samples studied stand as examples of complex magnetic layer stacks and represent advanced spin-valve structures ͑Fig. 1͒, designed to optimize the GMR effect.…”