Douglas Saunders

HAMR Performance and Integration Challenges

Heat-assisted magnetic recording (HAMR) is a fast evolving technology, and has been established as the next enabler of higher areal density in magnetic recording. After achieving high areal density capability, HAMR drive integration was recently demonstrated. In this paper, we discuss some of the recent learning from component performance and drive integration. We identify a key challenge in HAMR integration: erasure due to thermal background heating. The background heating was introduced to improve near-field transducer reliability and reduce laser power requirement. We present experimental and modeling data on the impact of thermal background, both in the cross-track (adjacent-track erasure) and down-track (self-erasure) dimensions.

Micro-magnetic and electric analysis on MR head baseline popping and instabilities

A general explanation for four types of instabilities in magneto-resistive (MR) recording heads is given. A micro-magnetic analysis of the root causes of the instabilities shows that baseline popping (BLP), permanent magnet reversal instability (PMRI), spiking noise and writer induced instability have the same root cause as random telegraph noise (RTN) which was reported previously. The details and differences in the formation of each individual phenomenon by the same cause have been investigated in this paper. An MR reader and pre-amplifier electric circuit simulation confirms that baseline popping is due to random telegraph baseline shift passing through a pre-amp DC blocking capacitor which is discharged and recharged at the two levels of the baseline.

Transition Curvature and Transition Broadening Analysis Using the Spin-Stand Imaging Technique

This paper presents an improved methodology of estimating transition curvature and transition broadening in perpendicular magnetic recording, using a spin-stand imaging technique. Due to the finite read resolution widths in the cross-track direction, the curvature and broadening of the measured transition will deviate from that in the magnetization. It is demonstrated that the reader width effects can be substantially eliminated by performing a specially designed trimming process which allows the reader to only see the written transitions from a small fraction of the track. Simulations illustrate that the trimming process effectively produces a narrow boxcar reader. This paper compares the results of this method for two heads with similar reader width but different writer width. It is shown that the trimming process has a stronger impact on the head with a larger ratio of reader width to writer width.

Junction edge instability in simple spin valve recording heads

Baseline popping (BLP) and baseline shift (BLS) in simple GMR heads has been studied experimentally. The instability occurs mainly at the sensors junction. Opening in the MR transfer curve is the source of the instability. This opening is caused by two local energy minima confined near one or both of the sensor edges, resulting in two free layer magnetization states. Media field plus thermal fluctuation can cause switching between these states.

HAMR Thermal Gradient Measurements and Analysis

The edge gradient of the thermal spot used to define bits in heat-assisted magnetic recording is a critical parameter in determining the quality of the magnetic transitions. We review the laser current modulation method used to measure this parameter and introduce the sideband ratio (SBR) approach as a fast, inexpensive technique for getting data on large volumes of heads or media. Mathematical derivation of the SBR method is given along with the details of implementation. Production level data on thousands of recording heads are used to illustrate its usefulness.

Empirical determination of areal density capability

A method is presented for determining the practical areal density capability of a magnetoresistive head/disk design from two quick error rate measurements. The method is generally independent of write width and track pitch and facilitates the direct comparison of MR readers or disk media.

Robust design of a permanent magnet stabilized high areal density magnetoresistive head

As the recording industry increases areal density every year, a magnetoresistive-soft adjacent layer (MR-SAL) head design is desirable with the following qualities: easy to be fabricated in large volume, capable of consistent and stable device-to-device performance, and enough signal to noise ratio to perform at high recording densities and data rates. A new type of MR head with these attributes is described for an areal density equal to 1444 Mb/in.2. The off-track characteristics of this MR head are determined by the sensor edge design which is defined by a permanent magnet (PM) layer. Improved off-track performance was achieved by substituting the spacer layer with the PM outside of the active sensor area. Excellent boundary control stabilization was obtained by the ferromagnetic exchange coupling between the PM and, the SAL and the MR layers. The bit error rate and electrical test results showed acceptable performance at 175 kbpi and 8250 tpi. The above MR head had average values of low frequency ampli...