S. M. Thompson

The discovery, development and future of GMR: The Nobel Prize 2007

One hundred and one years after J J Thomson was awarded the Nobel Prize for the discovery of the electron, the 2007 Nobel Prize for Physics was awarded to Professors Peter Grunberg and Albert Fert for the discovery of giant magnetoresistance (GMR) in which the spin as well as the charge of the electron is manipulated and exploited in nanoscale magnetic materials. The journey to GMR started with Lord Kelvin who 150 years ago in 1857 made the first observations of anisotropic magnetoresistance and includes Sir Neville Mott who in 1936 realized that electric current in metals could be considered as two independent spin channels. Modern technology also has a significant role to play in the award of this Nobel Prize: GMR is only manifest in nanoscale materials, and the development of nanotechnology growth techniques was a necessary pre-requisite; further, the considerable demands of the magnetic data storage industry to drive up the data density stored on a hard disk fuelled an enormous international research effort following the initial discovery with the result that more than 5 billion GMR read heads have been manufactured since 1997, ubiquitous in hard disks today. This technology drive continues to inspire exploration of the spin current in the field now known as spintronics, generating new ideas and applications. This review explores the science underpinning GMR and spintronics, the different routes to its discovery taken by Professors Grunberg and Fert, the new science, materials and applications that the discovery has triggered and the considerable potential for the future.

The magnetic properties of specially prepared pearlitic steels of varying carbon content as a function of plastic deformation

Abstract Specially prepared low carbon steels with pearlite fractions varying from 20% to 100% have been used to study the independent effects of pearlite fraction and tensile plastic deformation on the structure sensitive magnetic properties of low carbon pearlitic steels. In addition to bulk magnetic measurements, Barkhausen noise emissions were studied and domain wall motion observed directly using the technique of Lorentz electron microscopy. The magnetostrictive effects of residual stress and pinning effects of dislocation tangles were found to combine to cause the changes in the magnetic properties.

The art of sp↑n electron↓cs

Abstract A brief history is given of the nascent field of spin electronics in which the ability to differentially manipulate up- and down-spin current carriers is exploited. We discuss the impending marriage of spin-dependent effects with semiconductor technology and, in particular, the exploitation of spin-dependent transport in the semiconductors themselves. In this connection, preliminary experiments are described which explore spin transport in ion-implanted silicon. We conclude by evaluating various potential applications of the devices made possible by this exciting new development in electronic technology.

Spintronic materials and technology

Spintronic Materials and Characterizations Magneto-Optical Studies of Magnetic Oxide Semiconductors Synthesis and Characterization of Wide Band-Gap Semiconductor Spintronic Materials Magnetic Properties of (Ga,Mn)As-Based Magnetic Semiconductors Soft X-Ray Resonant Magnetic Scattering from Magnetic Nanostructures The Effect of Ru on Magnetization Switching and CPP-GMR Enhancement The Spin-Dependent Interfacial Transparency Spin Torque and Domain Wall Magneto Resistance Current-Driven Switching of Magnetization: Theory and Experiment Domain Wall Scattering and Current-Induced Switching in Ferromagnetic Wires-Experiment Domain Wall Magnetoresistance in Magnetic Nanowires-Theory Introduction to a Theory of Current-Driven Domain Wall Motion Spin-Injection and Spin Devices Silicon-Based Spin Electronic Devices: Toward a Spin Transistor Spin-LEDs: Fundamentals and Applications Spin Photoelectronic Devices Based on Fe and the Heusler Alloy Co2MnGa Electron Spin Filtering across a Ferromagnetic Metal/Semiconductor Interface Measured by Photoexcitation Ferromagnetic Metal/III-V Semiconductor Hybrid Spintronic Devices The Spin-Valve Transistor INDEX

The magnetic properties of pearlitic steels as a function of carbon content

Abstract Specially prepared low-carbon steels with pearlite fractions varying from 0.19 to 100% have been used to study the independent effect of carbon content and microstructure on the structure-sensitive magnetic properties of low-carbon pearlitic steels. Increased magnetic hardness with carbon content has been observed in the initial magnetisation and hysteresis curves. The changes in the magnetisation processes were investigated by studying the Barkhausen moise emissions and observing the domain wall motion directly using Lorentz electron microscopy. The increase in pearlite content significantly enhanced the effectiveness of cementite lamellae at pinning domain walls.

Infrared reflectance and magnetorefractive effects in metal–insulator CoFe–Al2O3 granular films

The infrared reflectance of (Co50Fe50)x–(Al2O3)1−x granular films which exhibit tunneling magnetoresistance has been measured in the wavelength range 2–25 μm for compositions both above and below the critical percolation volume fraction. The modifications of the Al2O3 Restrahlen reflection region are well accounted for in an effective medium model. In addition, frequency dependent changes of the reflection have been observed under the application of magnetic fields up to 12 kOe. At the longitudinal optic reflection edge around 9 μm distinctive magnetic signatures are found below and above the percolation threshold φc at x=0.17.

Influence of plastic deformation on Barkhausen power spectra in steels

Barkhausen power spectra and hysteresis curves have been measured for a pearlitic constructional steel over a range of plastic deformations up to 20%. The intercept of the power spectrum is seen to decrease with increasing deformation while the coercivity increases and both the permeability and remanence decrease. The results are discussed in the context of earlier reports and high-voltage electron microscopy studies.

Emissivity — a remote sensor of giant magnetoresistance

The link between emissivity in the mid-to-far-infrared regime and electrical conductivity is used to probe magnetoresistance. A direct relationship between the change in radiated flux and giant magnetoresistance is confirmed by experiment. The potential for spatially resolved measurements is also considered.

Importance of the interband contribution to the magneto-refractive effect in Co/Cu multilayers

The optical properties of Co/Cu multilayers are investigated theoretically using a multiband tight-binding model and the results are compared to experimental data on the magneto-refractive effect (MRE). The optical conductivity of both parallel and antiparallel configurations of Co/Cu multilayers is calculated using the Kubo–Greenwood formula. The Kramers–Kronig relations are utilized to obtain the imaginary part of the conductivity and the real part of the dielectric function. The conductivity is decomposed into the intraband and interband terms, so that their different contributions to the MRE may be analysed. In particular, we find that the competition between the intraband and interband contributions leads to a change of sign in the MRE as a function of frequency, a feature which is also observed experimentally in the infrared region. This is in contrast to the predictions of the Drude model, where only the intraband part of the conductivity is considered and the MRE curve always takes the same sign. Therefore, it is vital to include the interband contribution for a full spectral study of the origin of the infrared MRE data.

'Just in case' vs. 'Just in time': e-book purchasing models

Based on a breakout session held at the 33rd UKSG Conference, Edinburgh, April 2010 Case studies from the Universities of Leeds and York, together with the experiences of some libraries in the United States and Europe, are used to help demonstrate the range of purchasing options currently available to libraries. The advantages and disadvan- tages of routine title-by-title purchasing of e-books ‘just in case’ are examined, the emerging patron-driven ‘just in time’ model is explored, and the value of large publisher and aggregator e-book packages in com- parison to individual purchases is assessed.