Lung Tran

Dual stripe magnetoresistive heads for high density recording

The design and recording performance of dual stripe magnetoresistive read/inductive write heads with read widths of 4 /spl mu/m and write widths of 4.5 /spl mu/m are described. A linear density of 75 kfci (D50) was measured in heads with shield-to-shield spacing of 420 nm and 70 nm of dielectric separating the two magnetoresistive stripes. Large signal amplitude, linear cross-track profile, and good second harmonic suppression are observed in accordance with theoretical expectations. Readback waveforms contain little baseline shift and the ratio of positive to negative peak amplitudes is very close to unity. Stable signals are seen for heads with and without exchange stabilization. Conductor topography in the read head is replicated in the write head and can adversely affect cross-track behavior. Non-planarity of the write head must be considered in the design of shared pole magnetoresistive heads. >

DC modulation noise and demagnetizing fields in thin metallic media

Measurements of noise excited in magnetic recording media by a head energized by direct current yield a peak noise when the total field in the medium equals the remanent coercivity and opposes the original sense of medium saturation. The total field is the head field and a demagnetizing field stemming from a pseudotransition pinned under the head gap. This phenomenon has been studied experimentally by examining a thickness series of thin-film media with a wide range of demagnetizing ratios and by self-consistent calculations of this magnetizing process. Measurements of replay spectra were used to calibrate the record head. The demagnetizing field is about 19% of the remanent coercivity for a demagnetizing ratio of 767 nm. It is argued that careful calibration of this noise measurement yields an accurate in situ technique to monitor disk media coercivity or head efficiency variability. >

A magnetoresistive gradiometer for detection of perpendicularly recorded magnetic transitions

A magnetoresistive gradiometer to detect perpendicularly recorded transitions has been conceived. It utilizes two parallel magnetoresistive stripes with opposing sense/bias currents. The magnetoresistive elements mutually bias each other with the same polarity bias fields. The fields of a perpendicular transition centered between the two stripes increase the resistance of one stripe while decreasing that of the other, therefore providing maximum output signal using differential detection. The detector provides a Lorenztian‐type readback waveform and rejection of common‐mode noise. The experimental readback waveform exhibited a pulse width at half maximum of 0.7 μm for a head flying at 0.2 μm above the media surface.

Thermal variations in switching fields for sub-micron MRAM cells

Thermal effects in switching of sub-micron tunnel junctions are investigated. The switching field is shown to he inversely dependent on temperature, and switching field jitter is shown to be strong function of temperature. Micromagnetic modeling is used to understand thermal effects. In some instances a stability factor (defined as KV/kT) of 100 or more may be required for acceptable switching field jitter, while with proper optimization of FM layers, stability factors of 50 or 60 may suffice.

Delta-sigma digital magnetometer utilizing bistable spin-dependent-tunneling magnetic sensors

A digital magnetometer, utilizing a micron-sized spin-dependent-tunneling (SDT) sensor as a field-dependent bistable difference node within an oversampling first-order delta-sigma (Δ−Σ) analog-to-digital converter, was designed and prototyped. The Δ−Σ magnetometer can be fabricated as a single-chip device. It is intended for integration directly with digital components, facilitating development of low-cost magnetic-field sensing systems for commercial and military navigation, security, and linear-magnetic-field sensing applications. The Δ−Σ magnetometer operates by pulsing the SDT element along its hard axis (HA) in order to set the magnetization of the free layer into an unstable equilibrium orientation along the HA. In the absence of an easy-axis (EA) magnetic field, thermal fluctuations result in an equal probability for the magnetization to relax into one of the two stable orientations along the EA. Application of an EA magnetic field increases the probability for the magnetization to relax into the E...

3D analysis of MR readback on perpendicular medium

A 3-D analysis of magnetoresistive (MR) read on perpendicular media using the reciprocity method is presented. It is shown that the conduction of magnetic flux, obtained from an equivalent reciprocity field, away from the active area is an important phenomenon for this structure, and may introduce error if 2-D analysis is used. The authors examine the effect of shield width and show that when the shield width is equal to the width of the active area of the MR head, 3-D analysis closely resembles the 2-D results. This calculation is extended to a differentially connected dual element MR head for perpendicular recording. >

Pulsed current switching of submicrometer MRAM cell

Thermally assisted switching of submicrometer magnetic tunnel junctions is investigated. It is found that writing can be done with pulses of the order of 1 ns. Switching current and switching current jitter are seen as strong functions of temperature, whereas both are only weakly dependent on current pulse duration. Micromagnetic modeling using a stochastic Landau-Lifschitz equation is used to understand thermal effects. The simulation predicts the observed switching current but does not explain the magnitude of the switching current jitter.

Control of ferromagnetic coupling by in situ interface modification

Ferromagnetic coupling is a major factor in the engineering of magnetic multilayer devices. This article describes a method for controlling the interface roughness, which contributes to ferromagnetic coupling. Specifically, we report a process whereby the amplitude of the roughness profile can be systematically modified. Although the data presented is for pinned layer systems of NiFe on MnFe, this process is equally effective in other materials systems, such as CoFe and NiFeCo on IrMn. A reduction of the ferromagnetic coupling is evidenced by a decrease in the offset of the magnetic hysteresis loops from zero field, a reduction of roughness of the films, and an improvement in resistance uniformity.

Pulsed current switching of sub-micron MRAM cell

In this paper, we will report measurement and simulation of switching of sub-micron MRAM cells and also investigate the effect of temperature on the pulsed current switching of such devices. we will compare detailed micromagnetic simulation of MRAM switching using a stochastic Landau-Lifshitz equation.

Magnetic Recording Heads

The sections in this article are 1 Basic Operation 2 Types of Recording Heads 3 Head Materials and Processing 4 Theory of Operation 5 Recording Head Testing 6 Future Directions