Publications


Silicon-based spin electronic devices: Toward a spin transistor

in Spintronic Materials and Technology, (2006) 245-268

SM Thompson, D Pugh, D Loraine, CL Dennis, JF Gregg, C Sirisathitkul, W Allen

© 2007 by Taylor & Francis Group, LLC. A burgeoning trend in spin electronics is the development of spin-sensitive semiconductor devices. Implementing spin-polarized carriers in semiconductors expands potential device functionality by differentiating between up and down spin carriers in both the conduction and valence bands. This spin selectivity may be realized by using magnetic semiconductors or by employing external spin-selective ferromagnets to inject spin-polarized current into nonmagnetic semiconductors. As the length scales are reduced, ferromagnetic single electron devices become feasible.


Silicon spin diffusion transistor: materials, physics and device characteristics

IEE PROCEEDINGS-CIRCUITS DEVICES AND SYSTEMS 152 (2005) 340-354

CL Dennis, CV Tiusan, JF Gregg, GJ Ensell, SM Thompson


Tunnel barrier fabrication on Si and its impact on a spin transistor

J MAGN MAGN MATER 290 (2005) 1383-1386

CL Dennis, CV Tiusan, RA Ferreira, JF Gregg, GJ Ensell, SM Thompson, PP Freitas

The realization of many future spintronic devices requires efficient spin injection into semiconductor structures. A Critical considerations include interfacial intermixing of the metallic components and oxygen with Si, and the conditions for Schottky barrier formation. Both impact the design of a silicon-based spin transistor, which tunnel injects carriers from a ferromagnetic emitter into the Si base and then tunnel-collects them via a ferromagnetic collector. A discussion of the characteristics of this spin tunnel transistor will be presented, including its behavior and magnetic sensitivity. © 2004 Elsevier B.V. All rights reserved.


I-V asymmetry and magnetoresistance in nickel nanoconstrictions

J MAGN MAGN MATER 272-76 (2004) 1571-1572

O Cespedes, AR Rocha, S Lioret, M Viret, C Dennis, JF Gregg, S van Dijken, S Sanvito, JMD Coey

We present a joint experimental and theoretical study on the transport properties of nickel nanoconstrictions. The samples show highly non-linear and asymmetric I-V characteristics when the conductance is smaller than G(0) = 2e(2)/h, and huge magneto resistance ratios exceeding 99.9%. We model a single point contact in a two-band tight-binding model as a 2 x 2 nickel chain connected to two semi-infinite nickel leads. The magnetoresistance is calculated by using a non-equilibrium Green's function technique. (C) 2003 Published by Elsevier B.V.


A novel high gain silicon based spin transistor

Digests of the Intermag Conference (2003)

CL Dennis, C Sirisathitkul, GJ Ensell, JF Gregg, SM Thompson

A novel high gain silicon based spin transistor was presented. The spin transistors were fabricated using standard photolithography on n- and p-type silicon-on-insulator (SOI) wafers. The results showed that connected in common emitter configuration and measured at room temperature, the transistor exhibited similar characteristics to that of a conventional bipolar transistor, except the current gain is negative.


High current gain silicon-based spin transistor

Journal of Physics D: Applied Physics 36 (2003) 81-87

JF Gregg, Dennis, C. L.,, C. Sirisathitkul, G. J. Ensell


Spin injection efficiency in spin electronic devices

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 265 (2003) 274-289

JF Gregg, RP Borges, E Jouguelet, CL Dennis, I Petej, SM Thompson, K Ounadjela


A novel high gain silicon based spin transistor

Intermag 2003 - Program of the 2003 IEEE International Magnetics Conference (2003)

CL Dennis, C Sirisathitkul, GJ Ensell, JF Gregg, SM Thompson

© 2003 IEEE. In this paper, we fabricate a novel high gain silicon based spin transistor and measured the minority carrier transport in the silicon. When measured with a magnetic field applied in the plane of the transistor and perpendicular to the direction of the current flow, the I-V characteristics show a variation in the collector current causing the transistor to behave as a magnetically tunable device with a field dependent gain.


Comparative study of spin injection into metals and semiconductors

JOURNAL OF PHYSICS D-APPLIED PHYSICS 35 (2002) PII S0022-3727(02)30114-1

RP Borges, CL Dennis, JF Gregg, E Jouguelet, K Ounadjela, I Petej, SM Thompson, MJ Thornton


Spin-polarized electronic reflections at metal-oxide interfaces

J MAGN MAGN MATER 240 (2002) 140-142

V Da Costa, A Iovan, K Ounadjela, W Allen, JF Gregg, B Dieny

The ultra-thin oxide tunnel barrier employed in magnetic tunnel junctions stack has to be of very high quality in terms of large scale homogeneity of its thickness and height parameters. For controlling precisely oxidation kinetic, we used spin valves as an oxidation progress probe. By measuring the magnetoresistance effect versus the oxidation time we are able to detect under- or over-oxidation of the metallic material. This technique consists of analysing the ability of spin-dependent electron scattering at metal/oxide interfaces. (C) 2002 Elsevier Science B.V. All rights reserved.


Spin electronics - a review

JOURNAL OF PHYSICS D-APPLIED PHYSICS 35 (2002) PII S0022-3727(02)88955-0

JF Gregg, I Petej, E Jouguelet, C Dennis


Magnetoresistance through a single nickel atom

Physical Review B: Condensed Matter and Materials Physics 66 (2002) art. no.-220401

JF Gregg, I. Petej, M. Viret,, M. Gabureac


The defining length scales of mesomagnetism: A review

Journal of Physics Condensed Matter 14 (2002)

CL Dennis, RP Borges, LD Buda, U Ebels, JF Gregg, M Hehn, E Jouguelet, K Ounadjela, I Petej, IL Prejbeanu, MJ Thornton

This review is intended as an introduction to mesomagnetism, with an emphasis on what the defining length scales and their origins are. It includes a brief introduction to the mathematics of domains and domain walls before examining the domain patterns and their stability in 1D and 2D confined magnetic structures. This is followed by an investigation of the effects of size and temperature on confined magnetic structures. Then, the relationship between mesomagnetism and the developing field of spin electronics is discussed. In particular, the various types of magnetoresistance, with an emphasis on the theory and applications of giant magnetoresistance and tunneling magnetoresistance, are studied. Single electronics are briefly examined before concluding with an outlook on future developments in mesomagnetism.


Frequency domain magnetic measurements from Kilohertz to Gigahertz

TOP APPL PHYS 83 (2002) 217-243

JF Gregg

This review deals with practical aspects of making frequency-domain measurements of magnetic susceptibility and magnetic losses from 200 kHz up to 10 GHz. It sets out the types of measurement concerned, distinguishing resonant from nonresonant phenomena. The techniques available are categorized according to suitability for the different frequency regimes and types of investigation. Practical recipes are provided for undertaking such experiments across the entire frequency range. Marginal oscillator spectrometry is discussed which is applicable across the whole frequency range. Different instruments are presented, and particular emphasis is placed on designs which function on the Robinson principle. Analysis of oscillation condition and signal-to-noise performance is dealt with, also sample considerations such as filling factor. Practical circuits are presented and their merits and demerits evaluated. Layout and radio-frequency design considerations are dealt with. Ultrahigh/microwave frequency marginal oscillator spectrometry is given special treatment and several practical designs are given. The essentials of good microwave design are emphasized. A general discussion of resonant structures is included which treats multiple layer coil design, slow wave line structures, stripline and cavities. Unusual cavity designs such as the rhumbatron are treated. Use of striplines with microwave marginal spectrometry is described and compared with conventional network-analysis techniques. The use of parameter matrices for high-frequency analysis is alluded to. Some details of good construction practice are given together with some practical considerations relating to skin depth and other high-frequency phenomena.


Spin polarization of injected electrons

SCIENCE 296 (2002)

WF Egelhoff, MD Stiles, DP Pappas, DT Pierce, JM Byers, MB Johnson, BT Jonker, SF Alvarado, JF Gregg, JAC Bland, RA Buhrman


Spin polarized electronic reflections at metal-oxide interfaces: A technique for characterizing tunneling barriers in magnetic random access memory devices

J APPL PHYS 91 (2002) 7466-7468

K Ounadjela, V Da Costa, A Iovan, T Dimopoulos, F Dahmani, D Mahenthiran, B Dieny, W Allen, JF Gregg

One of the most critical steps in the realization of high quality tunneling devices is the fabrication of ultrathin oxide layers. This article describes a powerful technique for controlling the oxidation of ultrathin metallic layers. The technique consists of depositing the metallic layer to be oxidized on top of the soft magnetic layer of a bottom spin valve. The oxidation kinetics are then monitored by measuring the current in plane sheet resistance and magnetoresistance. The technique relies on the extreme sensitivity of the magnetoresistance on the degree of specular reflection at the soft magnetic layer/oxide interface. (C) 2002 American Institute of Physics.


Fabrication and characterisation of Ni nanocontacts

J MAGN MAGN MATER 242 (2002) 492-494

O Cespedes, MA Bari, C Dennis, JJ Versluijs, G Jan, J O'Sullivan, JF Gregg, JMD Coey

We propose a simple method to make metallic nanocontacts. A gap is electrochemically etched in a Ni track. The gap resistance is monitored as material is redeposited from the solution to bridge the gap. I:V characteristics were compared with those of Ni nanocontacts fabricated using a focussed ion beam (FIB). The I:V characteristic is asymmetric above 200 K in both cases. (C) 2002 Published by Elsevier Science B.V.


Versatile radiofrequency sensor

SENSOR ACTUAT A-PHYS 91 (2001) 39-41

RP Borges, M Bari, JMD Coey, JF Gregg, M Thornton, W Allen

A miniature, monolithic radiofrequency sensor operating with MESFET circuitry in the GHz range is able to detect a wide variety of magnetic, metallic and dielectric materials via the losses induced in the sensitive volume around a coil. Application of the sensor to detect plastic and metal gearwheels and falling liquid drops is illustrated; the signal-to-noise ratio falls off as the inverse distance from the coil to the liquid drop. (C) 2001 Elsevier Science B.V. All rights reserved.


Effect of silicon crystal structure on spin transmission through spin electronic devices

J APPL PHYS 87 (2000) 5161-5163

DR Loraine, DI Pugh, H Jenniches, R Kirschman, SM Thompson, W Allen, C Sirisathikul, JF Gregg

Spin injection into and spin transport through silicon spacer layers in iron/silicon/cobalt structures has been investigated. Ultrahigh vacuum evaporated silicon spacers of varying crystal quality from amorphous to epitaxial of thicknesses from 10 to 200 Angstrom were shown to improve their electrical conduction with increasing crystallinity, but no spin dependent transport was observed through the structure. Silicon and iron interdiffusion was also observed at the interfacial region. Device quality silicon was studied using 460 and 540 mu m doped silicon wafers of resistivity 0.1 and 1 Omega cm, respectively, polished on both sides, onto which were deposited iron and cobalt layers. Sharp metal-semiconductor interfaces were achieved in this way, but no spin dependent transport, putting an upper limit on the spin diffusion length in device quality silicon wafers. (C) 2000 American Institute of Physics. [S0021-8979(00)92808-1].


Evidence for a high T-c magnetic amorphous polymorph obtained by swift heavy ion irradiation

NUCL INSTRUM METH B 146 (1998) 260-264

M Ghidini, JP Nozieres, F Bolzoni, G Suran, JF Gregg, B Gervais

The intermetallic compound CeCo3 has been irradiated at GANIL by 1 GeV Pb-208 ion beams. The irradiated samples are found to be strongly amorphised. A track diameter of 8 nm is found. The magnetic properties of the irradiation induced CeCo3 amorphous phase have been studied in detail and found substantially different with respect to those of amorphous CeCo3 obtained by conventional methods. In particular, an increase of about 200 K in the Curie temperature is observed, suggesting that a different type of chemical short range order might have been stabilized by irradiation. (C) 1998 Elsevier Science B.V. All rights reserved.

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