Z.B. Guo

Nanchang University

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J. J. Qiu

State Key Laboratory of Chemical Engineering

P. Luo

Tianjin University of Commerce

Yihong Wu

Sun Yat-sen University

Y.K. Zheng

National University of Singapore

Gang Han

Nankai University

K.B. Li

Sun Yat-sen University

L.H. An

ShanghaiTech University

Gang Han

Jiangnan University

Wenbo Mi

Tianjin University

Z.Y. Liu

Data Storage Institute

Cooperative Institutions

Data Storage Institute

National University of Singapore

Chinese Academy of Sciences

Agency for Science, Technology and Research

Nanjing University

King Abdullah University of Science and Technology

University of Chinese Academy of Sciences

Nanyang Technological University

Institute of Physics

Nanchang University

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Ion Beam Modification of Exchange Coupling to Fabricate Patterned Media

Journal of Nanoscience and Nanotechnology (2011)

Mojtaba Ranjbar S. N. Piramanayagam R. Sbiaa Kyaw Oo Aung Z.B. Guo

For bit-patterned media, media with low remanent magnetization (M(r)) and high M(r) regions are needed for storing information, which is usually achieved by lithographically defining magnetic and non-magnetic regions. In this work, we have investigated the use of ion beam modification of media surface to define the low and high M(r) states using a medium that is at a low M(r) state to start with. The low M(r) state is achieved by the use of synthetic antiferromagnetic coupling obtained in Co-alloy/Ru/Co-alloy trilayer structured film. Local ion beam modification at 30 keV energy using Ga+ ions was used to create high M(r) regions. AFM and MFM observations indicated that patterned regions of low and high M(r) can be observed with ion beam irradiation. This technique is a potential method to achieve patterned media without the need of planarization techniques.

Patterned media

Recording media

Surface Modification

10.1166/jnn.2011.2704

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Citations (3)

Epitaxial growth of ferromagnetic Co:TiO2 thin films by co-sputtering

Journal of Magnetism and Magnetic Materials (2003)

Gang Han Yihong Wu M. Tay K.B. Li Z.B. Guo

10.1016/s0304-8853(03)00492-x

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Citations (14)

Magnetization reversal in exchange biased multilayers detected by giant magnetoresistance effects

INTERMAG Asia 2005. Digests of the IEEE International Magnetics Conference, 2005. (2005)

Z.B. Guo K.B. Li J. J. Qiu Gang Han Y.K. Zheng

A structure of exchange biased FM1/AFM1/FM2/AFM2 multilayers is proposed and giant magnetoresistance effect is used as a probe of magnetization reversal. A spin valve structure of NiFe (2 nm)/CoFe (1 nm)/Cu (2.2 nm)/NiFe (12 nm/IrMn (3 nm)/NiFe (6 nm)/IrMn (12 nm) is fabricated to investigate the magnetization reversal in NiFe (12 nm)/IrMn (3 nm)/NiFe (6 nm)/IrMn (12 nm) multilayers. In the decreasing field process, magnetization reversal can well be understood by the reversal of magnetization due to decreasing magnetization and increasing resistance. In the Increasing field process, magnetization and resistance increase sharply at the field around -20 Oe. Hysteresis loop of the sample are also investigated.

Hysteresis

Magnetization reversal

Exchange bias

Spin valve

10.1109/intmag.2005.1464456

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High Thermal Stable MRAM With a Synthetic Ferrimagnetic Pinned Layer

IEEE Transactions on Magnetics (2004)

Y.K. Zheng Yihong Wu K.B. Li J. J. Qiu Gang Han

Magnetic random access memory (MRAM) with a synthetic ferrimagnetic (SF) pinned layer has been investigated experimentally and theoretically. The SF pinned layer offers the higher thermal stability due to its even higher anisotropy and larger total thickness. A smaller aspect ratio cell with single domain state, less switching field dependence on the cell size, and lower switching field can be achieved in the SF structure than that in the conventional structure because of the thinner effective thickness. The experimental results show that high heat tolerance can also be achieved in the SF MRAM structure.

Ferrimagnetism

Magnetoresistive random-access memory

Thermal Stability

Aspect ratio (aeronautics)

10.1109/tmag.2004.830199

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Citations (2)

Prediction of two-dimensional diluted magnetic semiconductors: Doped monolayer MoS2systems

Physical Review B (2013)

Yingchun Cheng Zhiyong Zhu Wenbo Mi Z.B. Guo Udo Schwingenschlögl

Using first-principles calculations, we propose a two-dimensional diluted magnetic semiconductor: monolayer MoS${}_{2}$ doped by transition metals. Doping of transition metal atoms from the IIIB to VIB groups results in nonmagnetic states, since the number of valence electrons is smaller or equal to that of Mo. Doping of atoms from the VIIB to IIB groups becomes energetically less and less favorable. Magnetism is observed for Mn, Fe, Co, Zn, Cd, and Hg doping, while for the other dopants from these groups it is suppressed by Jahn-Teller distortions. Analysis of the binding energies and magnetic properties indicates that (Mo,$X$)S${}_{2}$ ($X=\text{Mn}$, Fe, Co, and Zn) are promising systems to explore two-dimensional diluted magnetic semiconductors.

Magnetic semiconductor

Magnetism

Valence electron

10.1103/physrevb.87.100401

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Citations (539)

Fabrication of graphene nanogap with crystallographically matching edges and its electron emission properties

Applied Physics Letters (2010)

Haomin Wang Zhen Zheng Y. Y. Wang Jiawen Qiu Z.B. Guo

We demonstrate the fabrication of graphene nanogap with crystallographically matching edges on SiO2Si substrates by divulsion. The current-voltage measurement is then performed in a high-vacuum chamber for a graphene nanogap with few hundred nanometers separation. The parallel edges help to build uniform electrical field and allow us to perform electron emission study on individual graphene. It was found that current-voltage characteristics are governed by the space-charge-limited flow of current at low biases while the FN model fits the I-V curves in high voltage regime. We also examined electrostatic gating effect of the vacuum electronic device. Graphene nanogap with atomically parallel edges may open up opportunities for both fundamental and applied research of vacuum nanoelectronics.

Nanoelectronics

Nanometre

10.1063/1.3291110

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Citations (46)

Low switching current flux-closed magnetoresistive random access memory

Journal of Applied Physics (2003)

Y.K. Zheng Yihong Wu K. B. Li J. J. Qiu Yatao Shen

A spin valve magnetoresistive random access memory with a flux-closed structure is presented. The flux-closed structure prevents the disruption to magnetization of the recording layer and increases the thermal stability. Simulation results show that the switching field increases under the uniform external field, however, the switching field has no change under the bit current field. Only the bit current that flows mostly at the center is used to switch the cell. Experimental results show that the bit current of 10 mA is sufficient to switch the 1 μm×4 μm cell.

Magnetoresistive random-access memory

Switching time

Spin valve

Commutation

10.1063/1.1557372

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Citations (6)

Sub-100-nm Current-Perpendicular-to-Plane Sensor Fabrication

IEEE Transactions on Magnetics (2004)

Y.K. Zheng K.B. Li J. J. Qiu Gang Han Z.B. Guo

Two sets of processes for sub-100-nm current-perpendicular-to-plane (CPP) spin-valves (SVs) were developed. In the first method, a CPP SV was fabricated by using via-hole instead of small cell patterning. This method makes it easy to characterize the CPP spin valve films. The shunting effect has been analyzed in this method. In the second method, a resist layer for planarization, ion-milling, and wet etching for self-opening via-hole in a self-aligned fashion by making use of the height difference between the cell and surrounding regions was introduced. This method is suitable for the actual recording heads with small dimension even without an ion-beam-deposition system. CPP sensors with size from 0.05 /spl mu/m/spl middot/0.05 /spl mu/m to 0.4 /spl mu/m/spl middot/ 0.5 /spl mu/m with different free- layer structures have been investigated by means of the first method.

Chemical Mechanical Planarization

Spin valve

Perpendicular recording

Patterned media

Critical dimension

Deposition

10.1109/tmag.2004.830204

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Citations (5)

Spin Flop Switching of the Guided Synthetic Antiferromagnet MRAM

IEEE Transactions on Magnetics (2006)

Yuqiao Zheng J.J. Qiu K.B. Li Gang Han Z.B. Guo

A magnetoresistance random access memory (MRAM) with a guided synthetic antiferromagnet (SAF) and direct writing scheme is presented to reduce the writing time. The MRAM cell includes not only the balanced SAF trilayers but also one more guiding layer, which is weakly exchange-coupled with one of the SAF layers. The two orthogonally oriented digital and word lines are aligned at 45deg with respect to the easy axis of the cell. With the exchange-coupling field from the guiding layer, the MRAM cell can be written directly by the combined field induced by current of the digital and word line. However, the cell cannot be switched by any single field induced by either current due to the balanced SAF structure before saturation. The switching field has been reduced and the writing operation margin has been improved with the use of the exchange-coupling field. Both simulation and the experiments have been carried out to verify this scheme. The write operation margin-H _disturb /H _sw of more than 4.3 has been achieved for the magnetic tunnel junction MRAM cell

Magnetoresistive random-access memory

Tunnel magnetoresistance

Saturation (graph theory)

10.1109/tmag.2006.879736

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Citations (2)

Saturation field direction dependence of domain structures in NiFe elements

Solid State Communications (2006)

Z.B. Guo Y.K. Zheng K.B. Li Gang Han Z.Y. Liu

Saturation (graph theory)

Metastability

10.1016/j.ssc.2006.06.039

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