CPP-GMRヘッドにおけるスピントルクノイズの解析

概要

論文の詳細を見る
Technologies for realizing areal recording densities of over 1 Tbit/inch2 in hard disk drives have been aggressively developed. At such high densities, it is necessary that a read head should be able to sense a weak magnetic field straying from a recorded medium. One of the most promising candidates for such a head is a current-perpendicular-to-plane giant magnetoresistive (CPP-GMR) head. However, it has been pointed out that in a CPP-GMR head, injection of polarized spin into a free layer causes spin-torque noise, which is peculiar to CPP-GMR heads. Several experimental and theoretical results on spin-torque noise have been reported. Thus, it is necessary to investigate the relationships of spin-torque noise with various parameters of a CPP-GMR head. In this paper, the dependencies of the spin-torque noise power and spectrum on the amplitude of the sense current density, its polarity, and the amplitude of the exchange interaction acting on the pinned layer are investigated by means of micromagnetic simulation. As a result, it is clarified that the noise properties are strongly influenced by the polarity of the injected spin, and that the noise power spectrum is located in narrow regions of frequency space.