IEEE TRANSACTIONS ON MAGNETICS, VOL. 41, NO. 10, OCTOBER 2005 3091 Micromagnetic Study of the Correlation Between Head Field Gradient and Jitter in Perpendicular Recording Jason S. Goldberg, Member, IEEE, Pierre Asselin, Member, IEEE, Sharat Batra, Member, IEEE, and Hong Zhou, Member, IEEE Research Division, Seagate Technology, Pittsburgh, PA 15222 USA Various write head field gradients are achieved by adjusting the design of a magnetic recording system consisting of a single pole head with a trailing shield flying over a hard magnetic layer with a soft underlayer. Micromagnetic simulations show that the transition jitter is not exactly inversely proportional to the head field gradient, and that this relationship is independent of system design. The effective field based on the Stoner–Wohlfarth coherent switching, instead of the perpendicular field, must be applied to calculate the head field gradient. Index Terms—Jitter, micromagnetic model, perpendicular magnetic recording, write head field gradient. I. INTRODUCTION T RANSITION position jitter is the dominant noise source in advanced perpendicular magnetic recording sys- tems. It has been demonstrated that is related to transition parameter and cross-track correlation length of the written transition [1]. According to the Williams–Comstock model [2], the transition parameter is inversely proportional to the head field gradient . Therefore, the jitter noise should be in- versely proportional to the head field gradient [3]. However, in the literature, both the perpendicular head field and the effective head field based on Stoner–Wohlfarth coherent switching have been used to calculate the head field gradient. Here, micromag- netic simulations were performed to analyze the correlation be- tween head field gradient and jitter. In this paper, we are not attempting to produce an optimal design for a recording system. Instead, we explore the rela- tionship between head field gradient and jitter and determine which head field gradient should be used for the jitter calcu- lation. To examine this relationship, a range of head field gra- dients was obtained by modeling two different designs of a single pole write head with a trailing shield and soft magnetic underlayer and changing: 1) the position of the hard magnetic layer by simultaneously varying the head-to-medium spacing and the interlayer thickness, while keeping the head-to-soft-un- derlayer spacing constant; 2) the pole-to-shield gap length; and 3) the head-to-soft-underlayer spacing via interlayer thickness variation. Reducing the spacing of the head to the hard magnetic layer (HMS) is one method for increasing write field gradient. HMS reduction is difficult due to process control tolerances. It would be useful to increase the write field gradient without relying on reducing HMS. Digital Object Identifier 10.1109/TMAG.2005.855318 TABLE I SYSTEM PARAMETERS II. SIMULATION DESCRIPTION A. Micromagnetic Model A micromagnetic read/write model consisting of a pseudo- Voronoi medium, a finite-element model (FEM) head field in the presence of a high permeability soft underlayer (SUL), and reci- procity playback is applied to simulate the recording system [4]. The recording system parameters are shown in Table I. These parameters were unchanged over all runs, except where noted in the table. The heads were single pole-type designs with trailing shields; the pole and shield were separated at the air-bearing surface (ABS) by a distance [5]. Head 1 had a write pole 0018-9464/$20.00 © 2005 IEEE