Ultrafast magnetization dynamics of spintronic nanostructures

Copyright © 2011 The Royal SocietyThe ultrafast (sub-nanosecond) magnetization dynamics of ferromagnetic thin films and elements that find application in spintronic devices is reviewed. The major advances in the understanding of magnetization dynamics in the two decades since the discovery of giant magnetoresistance and the prediction of spin-transfer torque are discussed, along with the plethora of new experimental techniques developed to make measurements on shorter length and time scales. Particular consideration is given to time-resolved measurements of the magneto-optical Kerr effect, and it is shown how a succession of studies performed with this technique has led to an improved understanding of the dynamics of nanoscale magnets. The dynamics can be surprisingly rich and complicated, with the latest studies of individual nanoscale elements showing that the dependence of the resonant mode spectrum upon the physical structure is still not well understood. Finally, the article surveys the prospects for development of high-frequency spintronic devices and highlights areas in which further study of fundamental properties will be required within the coming decade

Electron Beam Lithography patterning of superconducting and magnetic nanostructures for novel optical and spintronic devices

In this thesis novel, high-end superconducting and spintronic devices have been fabricated and characterized. In summary, the proposed work has been focused on the realization of nanowires, and more generally nanostructures, using the Electron Beam Lithography. Such a technology offers a powerful solution for nanofabrication able to conjugate spatial resolution, operation flexibility, and costs. Two main research fields has been explored: superconductive nanowires for advanced optical detection and nanostructures for magneto-resistance based devices

Antiferromagnetic spintronics

Antiferromagnetic materials could represent the future of spintronic applications thanks to the numerous interesting features they combine: they are robust against perturbation due to magnetic fields, produce no stray fields, display ultrafast dynamics and are capable of generating large magneto-transport effects. Intense research efforts over the past decade have been invested in unraveling spin transport properties in antiferromagnetic materials. Whether spin transport can be used to drive the antiferromagnetic order and how subsequent variations can be detected are some of the thrilling challenges currently being addressed. Antiferromagnetic spintronics started out with studies on spin transfer, and has undergone a definite revival in the last few years with the publication of pioneering articles on the use of spin-orbit interactions in antiferromagnets. This paradigm shift offers possibilities for radically new concepts for spin manipulation in electronics. Central to these endeavors are the need for predictive models, relevant disruptive materials and new experimental designs. This paper reviews the most prominent spintronic effects described based on theoretical and experimental analysis of antiferromagnetic materials. It also details some of the remaining bottlenecks and suggests possible avenues for future research

Phase Coexistence in Manganites

The doped perovskite manganite La1-xCaxMnO3 (0<x<1) has been extensively studied due to the interactions between the electronic, magnetic and crystal lattices, and the wide range of phases that can coexist. The region of greatest interest in the bulk material is around x~0.5, where there is often mesoscopic phase coexistence between a ferromagnetic metal (FM) and an antiferromagnetic insulator (AF). The first part of the dissertation describes a systematic study on a series of La1-xCaxMnO3 films deposited onto SrTiO3 (001) by pulsed laser deposition with compositions in the range 0.40<x<0.45. From electrical transport and magnetisation measurements, the limit of metallic behaviour was found to be x=0.41 whereas ferromagnetism was seen up to x=0.45. Although the transition temperatures of 150-200 K were comparable with the bulk material, the saturation moment at 20 K was about 40% of the fully spin-aligned value, which suggests the possibility of a phase separated mixture of FM and AF regions. The deviation from the bulk behaviour is thought to be due to substrate-induced strain altering the crystal symmetry and making the cubic ferromagnetic state less favourable. In the remainder of this work, the nature of phase separation in 60 nm La0.59Ca0.41MnO3 and La0.60Ca0.40MnO3 films is investigated. The effect of an external magnetic field is studied. A high-field magnetoresistance (∆ρ/ρB=0) of 41% in fields of 400 mT was observed for a La0.60Ca0.40MnO3 film, which, while not as large as the values previously reported in the literature, is still significant. The magnetic history of the films was found to be very significant, with the zero-field resistivity depending on the highest field applied. The isothermal time dependence of the resistivity was found to be exponential, with a time constant in the range 100-1000 s. Possible mechanisms for the MR effect and the dependence on magnetic history are discussed.EPSR