Micromagnetics of perpendicular write heads with extremely small pole tip dimensions

Abstract

A three-dimensional micromagnetic model has been developed to study single pole write heads with soft magnetic underlayer ͑SUL͒ for perpendicular recording at extremely small track widths. The study points out that at any practical ABS-to-SUL spacing, the maximum head field within the recording media at deep submicron track width and pole-tip thickness becomes significantly smaller than the ideal value of 4M s . Head field gradient in the medium also degrades with decreasing track width. Maintaining the conventional design, a significantly large remanent head field develops for track width below 100 nm, presenting danger of erasing previously recorded bits. The origin of the large remanent head field is the failure for a pole tip to reach a completely demagnetized state due to the overwhelming ferromagnetic exchange energy at the deep submicron pole-tip dimensions.

Read and write processes, and head technology for perpendicular recording

“…The field from the surface charge on the write pole tip air bearing surface (ABS) can be solved analytically. The result shows a smaller field overall but with similar decay rate vs. write pole dimension [48]. This is because the analytical formula in Ref.…”

“…These two different responses are from two different assumptions, whether the surface magnetization is perpendicular to the charge surface or perpendicular to the medium surface, respectively, when the write pole is saturated. The results show that given different assumptions about the write head saturation, there exists an optimal angle to achieve maximum on-track field [47][48][49][50][51]. Note that as previously argued, achieving maximum on-track field is only one aspect in optimizing the slope angle.…”

Dependence of the pole-tip remanence on the medium magnetization state underneath the trailing shield of a perpendicular write head

“…The nonzero residual magnetization of an unlaminated pole tip after writing is a natural consequence of the pole-tip dimension rapidly approaching the material exchange length. 1,2 The problem could be further aggravated by local magnetocrystalline anisotropy of large crystallites in the pole tip.…”

Thermal Stability Enhancement of Perpendicular Media With High-Order Uniaxial Anisotropy

“…These media properties provide better thermal stability in perpendicular recording. However, this advantage is diminished as the dimension of the pole tip is reduced to increase the areal recording density [1]. The tradeoff between head writing field and thermal stability may still limit the achievable areal density for perpendicular recording.…”