Apirat Siritaratiwat

Design and Micromagnetic Simulation of Fe/L10-FePt/Fe Trilayer for Exchange Coupled Composite Bit Patterned Media at Ultrahigh Areal Density

Exchange coupled composite bit patterned media (ECC-BPM) are one candidate to solve the trilemma issues, overcome superparamagnetic limitations, and obtain ultrahigh areal density. In this work, the ECC continuous media and ECC-BPM of Fe/L10-FePt/Fe trilayer schemes are proposed and investigated based on the Landau-Lifshitz-Gilbert equation. The switching field, , of the hard phase in the proposed continuous ECC trilayer media structure is reduced below the maximum write head field at interlayer exchange coupling between hard and soft phases, , higher than 20 pJ/m and its value is lower than that for continuous L10-FePt single layer media and L10-FePt/Fe bilayer. Furthermore, the of the proposed ECC-BPM is lower than the maximum write head field with exchange coupling coefficient between neighboring dots of 5 pJ/m and over 10 pJ/m. Therefore, the proposed ECC-BPM trilayer has the highest potential and is suitable for ultrahigh areal density magnetic recording technology at ultrahigh areal density. The results of this work may be gainful idea for nanopatterning in magnetic media nanotechnology.

A novel technique to detect effects of electromagnetic interference by electrostatic discharge simulator to test parameters of tunneling magnetoresistive read heads

Electrostatic discharge (ESD) has been a significant problem in the manufacturing processes of the magnetic recording head technologies for many years. Besides direct discharge damage, ESD can also generate electromagnetic interference (EMI) which could possibly cause failure in magnetic read heads. The aims of this work are to measure the EMI from ESD simulator based on the standard IEC 61000-4-2 and to investigate the effects of EMI on tunneling magnetoresistive (TMR) read heads. The discharge current and the EMI generated by ESD simulator are measured in the experiment. Also, the EMI is applied to the TMR read heads at various amplitudes and distances in order to evaluate the changes of read head parameters including the bit error rate, resistance, read back signal amplitude, and asymmetry parameter of the head. The results show that the discharge current waveform is consistent with the IEC standard current waveform. In addition, it is found that the EMI is insufficient to cause a permanent change of t...

Magnetic Instability in Tunneling Magnetoresistive Heads Due to Temperature Increase During Electrostatic Discharge

Recently, there has been a growing interest in the effects of electrostatic discharge (ESD) failure on tunneling magnetoresistive (TMR) recording heads because it directly affects reliability in manufacturing of these heads. Therefore, we study the magnetic degradation in TMR junctions caused by the temperature increase using three different ESD models. A 3-D finite-element method is used for analyzing the spatial and temporal profiles of the temperature during the discharge. The results from the three models show that, although the highest temperature occurs in the MgO barrier layer, the initial magnetic modification likely arises in the IrMn antiferromagnetic layer due to its low Néel temperature. We also found that the increase in temperature is proportional to the square of the ESD voltage. The magnetic instability of the antiferromagnetic layer due to the ESD effect is the important parameter realized for development of the future TMR devices.

An EMI Immunity Study of TMR Heads in Quasi-Static Tester due to the Direction of Sweeping Frequency

This report aims to investigate a comparative effect of Electromagnetic Interference (EMI) on recording heads due to sweeping directions of low-to-high and high-to-low frequencies. Four selected Quasi-Static Tester (QST) parameters; MR resistance, MR amplitude asymmetry, Barkhausen noise and Hysteresis, are used for monitoring the effect of EMI on Head Gimbal Assembly (HGA). It is undoubtedly found that the Asymmetry and Hysteresis parameters provide insufficient indication of EMI effect for both sweeping frequency directions. On the other hand, it is discovered that the sweeping direction of the low-to-high frequency is more effective to two test parameters; MR resistance and Barkhausen noise, than the other direction. The dramatic energy accumulation is possibly explained this phenomenon but this energy level is not high enough to cause the Hysteresis change.

An Experimental Study of Head Instabilities in TMR Sensors for Magnetic Recording Heads with Adaptive Flying Height

We did an experimental study to investigate the effect of the thermal stress due to the heater for adjusting adaptive flying height (AFH) on the readability and instability of tunneling magnetoresistance (TMR) sensors. The slider head consists of a small heater nearby the read/write elements for controlling the clearance between the read/write elements and the recording medium of the magnetic recording system. It is firstly reported that the thermal stress from the AFH heater induces instabilities and caused head degradation. The thermal stress degrades the reader performance by inducing voltage fluctuations and large noise spikes that causes the magnetic recording system having poor bit error rate (BER). The open loop of the transfer curve indicates that the flipping of a synthetic antiferromagnet (SAF) edge magnetization causes these instabilities. The thermal stress reduces the exchange bias field and the energy barrier to flop the SAF edge magnetization. The dispersion and thermal stability of the antiferromagnetic (AFM) layer are the potential root causes of these SAF instabilities because the larger AFM dispersion in these heads gives less net stabilizing field to SAF layers that lowers the energy barrier to flop the SAF edge magnetization. Scanning electron microscope (SEM) images of these weak heads show rough surface and scratches close to the sensor element. The mechanical stress due to these scratches may additionally impact to the stabilizing field of the SAF.

Crosstalk Suppression in High Data Rate and High Density Hard Disk Drive Interconnects Using Magnetic Composites

Abstract Due to the increasing data transfer rates in hard disk drives, the crosstalk has become a source of operation failures during electrical and magnetic testing. In order to reduce this detrimental effect, the differential mode signal system of high-speed and high-density interconnects based on a new magnetic technique is proposed. The scattering parameters are evaluated in terms of the crosstalk and the transmission parameters, and then calculated using the 3D full wave simulation software. From the results, it is found that the proposed technique can suppress the near-end crosstalk and far-end crosstalk in a wide range of 1–20 GHz. In addition, the transmission signal levels from the proposed structure are still comparable to the conventional structure. Hence, the proposed technique provides an effective reduction of crosstalk, while maintaining the comparable transmission signal in a wide range of frequency.

CONFINED-CHALCOGENIDE PHASE CHANGE MEMORY WITH THIN METAL INTERLAYER FOR LOW RESET CURRENT BY FINITE ELEMENT MODELING

This paper reports on the confined-chalcogenide phase change memory with thin metal interlayer (CCTMI) with the operating reset current of 0.6mA-30ns. This cell offers low reset current with simple architecture and fabrication. Thermal and heat flux distribution of both the normal-bottom-contact (NBC) and a proposed CCTMI PCM cells were carefully analyzed and simulated by two-dimensional finite element modeling. It is intriguingly found that the reset operation current of the CCTMI cell is 44% lower than that of the NBC. CCTMI has capability to solve an over-programming fail issue due to confined heat dissipation in active area.

Anomalous magnetic responsiveness of giant magnetoresistive heads under specific electromagnetic interference frequencies using quasistatic tester

The giant magnetoresistive (GMR) heads have been used in the computer industry for decade. Recently, the anomalous performance caused by cell phones or external electromagnetic interference (EMI) is reported [V. Kraz and A. Wallash, J. Electrost. 54, 39 (2002)]; [Kruesubthaworn et al., J. Magn. Magn. Mater. 316, e142 (2007)] This prompts an experimental study of an anomalous magnetic disturbance to the heads under ascending and descending frequency variations. The rf generator with predetermined output is set for 30–1000MHz swept frequency in both directions, with the antenna being horizontal and vertical orientations. Five quasistatic tester (QST) parameters; magnetoresistive (MR) resistance, MR amplitude, asymmetry, Barkhausen noise, and hysteresis are used as markers in the EMI sensitivity study of head gimbal assembly. It is found that the worst change of MR amplitude is 10.2% (marginally over the norm), which occurs at 910MHz during ascending swept frequency and horizontal polarization. The largest v...

A study of noise effects due to the diode protection for shield resistance measurement of GMR recording heads

This paper examines the noise effects of protection diodes used for preventing voltage breakdown during magnetoresistive (MR)-shield resistance measurement in quasi-static test (QST) for giant magnetoresistive heads (GMR). Two forms of diode protection will be presented and the noise behavior of them will be discussed and compared in the context of the GMR Noise test.

The temperature and electromagnetic field distributions of heat-assisted magnetic recording for bit-patterned media at ultrahigh areal density

In this paper, the temperature and electromagnetic field distributions for bit-patterned media (BPM) with heat-assisted writing technology at areal density of 6.54–17.92 Tb/in2 are investigated by the finite integral technique method. We have found that the BPM can confine temperature better than continuous media. The temperature ratio of neighbor bits to heating bit of BPM at areal density of 6.54–7.69 Tb/in2 is lower than 65% and increases with increasing areal density. The electric field direction is toward the bit and the magnetic field circulates around the heating bit. In addition, the electric field of BPM is the same pattern as continuous media at areal density of 13.17 Tb/in2 or above.