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Dive into the research topics where Kaizhong Gao is active.

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Featured researches published by Kaizhong Gao.


ieee international magnetics conference | 2006

Recording on Bit-Patterned Media at Densities of 1 Tb/in

Hans Jurgen Richter; Alexander Yulievich Dobin; Kaizhong Gao; Olle Heinonen; R.J.M. van de Veerdonk; R. T. Lynch; Jianhua Xue; D. Weller; Pierre Asselin; Mehmet Fatih Erden; Richard Michael Brockie

We present a comprehensive analysis of the areal density potential of a bit-patterned media recording. The recording performance is dominated by written-in errors rather than traditional signal-to-noise considerations. Written-in errors are caused by statistical fluctuations of the magnetic properties and the locations of the individual dots. The highest areal densities are obtained with a combination of a pole head, a soft magnetic underlayer, and a storage medium of the composite type. Areal density scenarios of up to 5 Tb/in2 are analyzedRecording on bit-patterned media, BPM, is one way to postpone the superparamagnetic limit to higher densities. Here we investigate the recording potential of BPM. The fundamental idea of bit-patterned media is that one grain represents one bit so that the entire volume of the bit resists the effect of thermal agitation and higher recording density can be achieved. Previous investigations of a BPM recording system have shown that recording densities greater than 1 Tb/in2 should be possible [2].


IEEE Transactions on Magnetics | 2013

^2

Alexander Q. Wu; Yukiko Kubota; Timothy J. Klemmer; Tim Rausch; Chubing Peng; Yingguo Peng; Darren Karns; Xiaobin Zhu; Yinfeng Ding; Eric K. C. Chang; Yongjun Zhao; Hua Zhou; Kaizhong Gao; Jan-Ulrich Thiele; Mike Seigler; Ganping Ju; Edward Charles Gage

Heat-assisted magnetic recording (HAMR) is being developed as the next-generation magnetic recording technology. Critical aspects of this technology, such as plasmonic near-field transducer (NFT) and high anisotropy granular FePt media, have been demonstrated and reported. However, progress with areal density was limited until recently. In this paper, we report a basic technology demonstration (BTD) of HAMR, at 1.007 Tbpsi with a linear density of 1975 kBPI and track density of 510 kTPI, resulting from advances in magnetic recording heads with NFT and FePtX media. This demonstration not only shows significant areal density improvement over previously reported HAMR demos, more significantly, it shows HAMR recording at a much higher linear density compared to previous reports. It is an important milestone for the development of such a new technology. Many challenges still remain to bring this technology to market, such as system reliability and further advancement of areal density.


Nanophotonics | 2014

and Beyond

Nan Zhou; Xianfan Xu; Aaron T. Hammack; Barry C. Stipe; Kaizhong Gao; Werner Scholz; Edward Charles Gage

Abstract Plasmonic devices, made of apertures or antennas, have played significant roles in advancing the fields of optics and opto-electronics by offering subwavelength manipulation of light in the visible and near infrared frequencies. The development of heat-assisted magnetic recording (HAMR) opens up a new application of plasmonic nanostructures, where they act as near field transducers (NFTs) to locally and temporally heat a sub-diffraction-limited region in the recording medium above its Curie temperature to reduce the magnetic coercivity. This allows use of very small grain volume in the medium while still maintaining data thermal stability, and increasing storage density in the next generation hard disk drives (HDDs). In this paper, we review different plasmonic NFT designs that are promising to be applied in HAMR. We focus on the mechanisms contributing to the coupling and confinement of optical energy. We also illustrate the self-heating issue in NFT materials associated with the generation of a confined optical spot, which could result in degradation of performance and failure of components. The possibility of using alternative plasmonic materials will be discussed.


IEEE Transactions on Magnetics | 2013

HAMR Areal Density Demonstration of 1+ Tbpsi on Spinstand

Xiaobin Wang; Kaizhong Gao; Hua Zhou; Amit Vasant Itagi; Mike Seigler; Edward Charles Gage

Heat-assisted magnetic recording (HAMR) limitations and extendibility are studied in light of the recent 1.0 Tb/in2 technology demonstration. The paper examines HAMR specific technology challenges, including switching field distributions at elevated temperature, saturation noise, and near-field transducer (NFT) thermal spot-size limits. While current HAMR recording density ( ~ 1 Tb/in2) is limited by switching field distribution and thermal spot size, ultimate HAMR density (up to 5 Tb/in2) is determined by achievable recording-layer magnetic anisotropy and grain size.


IEEE Transactions on Magnetics | 2010

Plasmonic near-field transducer for heat-assisted magnetic recording

Yonghua Chen; Dion Song; Jiaoming Qiu; Paul Kolbo; Lei Wang; Qing He; Mark William Covington; Scott Stokes; Victor Boris Sapozhnikov; Dimitar V. Dimitrov; Kaizhong Gao; Bradley H. Miller

We review the 2 Tbit/in2 reader design landscape based on existing knowledge and projection. We found that the reader signal-to-noise ratio (SNR) requirement will be highly challenging due to the rapid increase in noise and the additional requirements from assisted writing. An acceptable level of channel bit density can be achieved in spite of a slow head-to-media spacing (HMS) reduction provided that both the shield-to-shield (SS) spacing and the ¿a¿ parameter scale with the bit length. We expect the side reading control for high ktpi to be difficult, and potentially a reader side shield will be required. The reader will likely use a higher quality MgO tunneling giant magnetoresistance (TGMR) stack with improved permanent-magnet coercivity. Certain new structures such as the differential reader or the trilayer will likely be part of the solution.


IEEE Transactions on Magnetics | 2002

HAMR Recording Limitations and Extendibility

Kaizhong Gao; H.N. Bertram

We have developed a three-dimensional micromagnetic perpendicular recording model to analyze high-density perpendicular write fields. Here, we compare a tapered-neck pole with a very small throat height to various write pole designs for a single-pole head. In studying the effects of throat height and write pole-return pole spacing, we found that, for a large throat height, both the write field and field gradient decrease as the throat height increases. The write field shape changes significantly at the leading edge for a write pole-return pole spacing less than 300 nm. The effects of soft-underlayer (SUL) permeability, saturation, and thickness basically follow the analytical formula. The net recording field is almost constant for SUL permeability above about 50.


Applied Physics Letters | 2010

2

Xiaobin Wang; Kaizhong Gao; Julius Hohlfeld; Mike Seigler

In order to achieve higher areal density, magnetization transition width must be reduced. This requires small media switching field distribution (SFD). Here we explore SFD and transition width in heat assisted magnetic recording and microwave assisted magnetic recording. We reveal that for energy assisted magnetic recording, additional SFD broadening exists as compare to conventional perpendicular recording. We show the effect of SFD broadening on transition width and the implications to the magnetic recording system as the areal density increases.


Journal of Applied Physics | 2006

{\hbox{Tbit/in}}^{2}

Kaizhong Gao; Juan Fernandez-de-Castro

This paper describes the energy surface model for two exchange coupled magnetic particles and a study of the critical switching field in this coupled system. It is shown that for static switching, the total energy is continuously reduced during the reversal process. The critical switching fields versus applied field angle can be directly obtained from the energy surface model. The results are in good agreement with micromagnetic simulation. For a fast dynamic switching with small damping, the critical switching field may be further reduced. In addition, it is shown that an increase in either Ms or the grain volume of the soft particle will lead to a further reduction of the switching field. This is primarily due to an increase in the Zeeman energy that changes during the reversal.


IEEE Transactions on Magnetics | 2010

Reader Design Outlook

Sumei Wang; Dan Wei; Kaizhong Gao

In this work, the microstructure and the magnetostriction effect of the FeCo thin film are considered in micromagnetic simulations; therefore the magnetic properties of the FeCo thin film and write pole can be calculated more accurately. Based on the micromagnetic models, magnetic hysteresis loops of films are calculated. The simulation results show that the magnetostriction has great effect on the coercive force of FeCo films. Furthermore, the initial permeability and the dynamic response of the FeCo write pole are studied. When the easy axis of the write pole is along cross-track direction, a 128 nm-wide and 32 nm × 32 nm-ABS pole tip has a real initial permeability of 8.0 at low frequencies and a roll-off frequency of 5.0 GHz. The effect of the easy axis orientation is also studied. The write field is about 4300 Oe with a reversal time of approximately 0.15 ns. The scaling of the permeability is analyzed by a simple micromagnetic model without microstructure.


Journal of Applied Physics | 2005

Write field analysis and write pole design in perpendicular recording

Haiwen Xi; Yiming Shi; Kaizhong Gao

We have theoretically investigated the ferromagnetic resonance in the magnetic thin film structures under the influence of spin-transfer torque using a modified Landau–Lifshitz–Gilbert equation in the linearization regime. The study shows that spin currents do not shift the resonance field but rather change both the resonance amplitude and the linewidth. Ferromagnetic resonance under this circumstance can be characterized by an effective damping constant. Depending upon its direction, the spin current can pump energy into or dissipate energy from the magnetic system. In addition, the quality factor of the resonance can be tuned by changing the current intensity. Ferromagnetic resonance excited by ac electrical currents is also theoretically demonstrated and discussed in this article.

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Olle Heinonen

Argonne National Laboratory

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