Imaging the equilibrium state and magnetization dynamics of partially built hard disk write heads

Abstract

Four different designs of partially built hard disk write heads with a yoke comprising four repeats of NiFe (1 nm)/CoFe (50 nm) were studied by both x-ray photoemission electron microscopy (XPEEM) and time-resolved scanning Kerr microscopy (TRSKM). These techniques were used to investigate the static equilibrium domain configuration and the magnetodynamic response across the entire structure, respectively. Simulations and previous TRSKM studies have made proposals for the equilibrium domain configuration of similar structures, but no direct observation of the equilibrium state of the writers has yet been made. In this study, static XPEEM images of the equilibrium state of writer structures were acquired using x-ray magnetic circular dichroism as the contrast mechanism. These images suggest that the crystalline anisotropy dominates the equilibrium state domain configuration, but competition with shape anisotropy ultimately determines the stability of the equilibrium state. Dynamic TRSKM images were acquired from nominally identical devices. These images suggest that a longer confluence region may hinder flux conduction from the yoke into the pole tip: the shorter confluence region exhibits clear flux beaming along the symmetry axis, whereas the longer confluence region causes flux to conduct along one edge of the writer. The observed variations in dynamic response agree well with the differences in the equilibrium magnetization configuration visible in the XPEEM images, confirming that minor variations in the geometric design of the writer structure can have significant effects on the process of flux beaming.

Time-resolved scanning Kerr microscopy of flux beam formation in hard disk write heads

“…An equilibrium magnetic state for nominally identical devices of this shape has been reported previously, 9 and is reproduced in Fig. 10.…”

“…Furthermore, the equilibrium state of these writers has been inferred from TRSKM measurements 8 and later directly observed by x-ray photoemission electron microscopy. 9 However, time-resolved imagery of flux beams has only been recorded at a resolution of ≈ 0.5 ns. Little attention has been paid to the precise nature of the process of formation of these flux beams on the leading edge of the waveform, nor to the spatial character of the flux beams during the write process.…”

A platform for time-resolved scanning Kerr microscopy in the near-field

“…The flexibility of TRSKM has also permitted dynamical studies of magnetic vortices [24][25][26][27][28][29], rings [30,31], domain walls [32], microwave assisted magnetic switching [33], and hard disk writers for perpendicular media disks [34][35][36]. In the last decade, emerging phenomena in spintronics have also been explored using TRSKM.…”