Advanced Magnetic and Optical Materials

Ashutosh Tiwari, Parameswar K. Iyer, Vijay Kumar, Hendrik Swart, Ashutosh Tiwari, Parameswar K. Iyer, Vijay Kumar, Hendrik Swart

• Publisher: Wiley-Scrivener
• Year: 2016
• Print ISBN: 9781119241911
• eBook ISBN: 9781119241959
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Civil Engineering
• Index: Technology & Engineering

Advanced Magnetic and OpticalMaterials offers detailed up-to-date chapters on the functional optical and magnetic materials, engineering of quantum structures, high-tech magnets, characterization and new applications. It brings together innovative methodologies and strategies adopted in the research and development of the subject and all the contributors are established specialists in the research area. The 14 chapters are organized in two parts:

Part 1: Magnetic Materials

• Magnetic Heterostructures and superconducting order
• Magnetic Antiresonance in nanocomposites
• Magnetic bioactive glass-ceramics for bone healing and hyperthermic treatment of solid tumors
• Magnetic iron oxide nanoparticles
• Magnetic nanomaterial-based anticancer therapy
• Theoretical study of strained carbon-based nanobelts: Structural, energetical, electronic, and magnetic properties
• Room temperature molecular magnets – Modeling and applications

Part 2: Optical Materials

• Advances and future of white LED phosphors for solid-state lighting
• Design of luminescent materials with "Turn-on/off" response for anions and cations
• Recent advancements in luminescent materials and their potential applications
• Strongly confined quantum dots: Emission limiting, photonic doping, and magneto-optical effects
• Microstructure characterization of some quantum dots synthesized by mechanical alloying
• Advances in functional luminescent materials and phosphors
• Development in organic light emitting materials and their potential applications

Part 1
MAGNETIC MATERIALS

Chapter 1
Superconducting Order in Magnetic Heterostructures

Sol H. Jacobsen, Jabir Ali Ouassou and Jacob Linder^*

Department of Physics, NTNU, Norwegian University of Science and Technology, Trondheim, Norway

^*Corresponding author: [email protected]

Abstract

In the rapidly developing field of spintronics, information is encoded and processed in the form of quantum spins. Although phenomena such as the giant magnetoresistance effect and spin-transfer torque have already found use in commercialized devices, two main challenges remaining in spintronic circuits based on electron transport are Joule heating and short decay lengths due to spin-flip scattering. The incorporation of superconducting elements into spintronic architectures has recently emerged as a potential solution to this problem. Recent advances in understanding the underlying physics of the interface between superconductors and ferromagnets has revealed a wealth of new features that can be enhanced and controlled to create improved spintronic devices. In this chapter, we present an introduction to the superconducting proximity effect in magnetic materials that opens the tantalizing prospect of combining the dissipationless transport offered by superconductors with the spin-polarized order existing in magnetic thin-film heterostructures. This includes an outline of theoretical frameworks and conventions in the field, as well as a discussion of some key experimental and theoretical advances that may indicate where the field is heading.

Keywords: Superconducting spintronics, proximity effect, ferromagnetism

1.1 Introduction

In the rapidly developing field of spintronics, information is encoded and processed in the form of quantum spins – either in place of, or in conjunction with, the traditional charge-based processing schemes. This has high potential with respect to computational processing, both in terms of time and energy efficiency, as well as significantly increased stability and longer coherence times than conventional electronic components. Although several spintronic architectures have already been widely adopted, e.g. in hard drives and random access memory based on the giant magnetoresistive effect (GMR) [1, 2], two main challenges in spintronic circuits based on electron transport are Joule heating and short decay lengths due to spin-flip scattering. The incorporation of superconducting elements into existing spintronic architectures has recently emerged as a potential solution to this problem [3]. Recent advances in understanding the underlying physics of the interface between superconductors and ferromagnets has revealed a wealth of new features that can be enhanced and controlled to create improved spintronic devices. In this chapter, we present an introduction to the superconducting proximity effect that opens the tantalizing prospect of combining the dissipationless transport offered by superconductors with the spin-polarized order existing in magnetic thin-film heterostructures. This includes an outline of theoretical frameworks and conventions in the field, as well as a discussion of some key experimental and theoretical advances that may indicate where the field is heading.

Spin-polarized currents are typically generated by passing an electric current through a ferromagnet, such that the magnetization in the ferromagnet acts to align the electron spins. Spintronic nanostructures are designed as a series of thin-film layers of normal-metal and ferromagnetic elements, which can be incorporated into conventional semiconductor-based systems. Emergent features of such spintronic devices can then be used to harness and control aspects of the device, for which GMR provides an exemplary case. GMR manifests as a change in the electrical resistance according to the relative magnetization directions of adjacent ferromagnetic layers: the resistance is low for parallel alignment and high for antiparallel alignment. This effect has been implemented in a wide variety of experimental structures, an important example being spin valves [4, 5], which switch an electric current on or off based on a magnetic input signal. Experimentally, spin valves consist of two ferromagnetic layers and an interstitial normal metal. The coercivity of one ferromagnetic layer can be enhanced due to proximity with an antiferromagnetic base layer, meaning that the application of an external magnetic field can be used to control the magnetization of the other ferromagnet. Albert Fert and Peter Grünberg shared the 2007 Nobel Prize in Physics for the discovery of the GMR effect.

In order to utilize the GMR effect, one needs a way to alter the magnetization direction of a ferromagnet. Spin-polarized electric currents can induce magnetization dynamics via the so-called spin-transfer torque effect [6, 7], but this typically requires very large current densities of order 10⁶ A/cm². This causes excessive Joule heating and ultimately destroys the properties of the thin-film structure. Recent investigations of the proximity effect, where the properties of adjacent materials leak across the interfacial barrier, have indicated that it will be possible to harness the dissipationless currents offered by superconductors to overcome the problem of excessive heating by making these supercurrents spin-polarized [3].

Superconductivity was discovered as early as 1911, when Heike Kamerlingh Onnes observed that the electrical resistivtiy of certain materials vanished abruptly at cryogenic temperatures [8]. Kamerlingh Onnes received the Nobel Prize in Physics in 1913 for this discovery. The temperature at which the transition to zero resistivity occurs is called the critical temperature (T_c) of the material, and as a material transitions into this superconducting state it displays a second characteristic ...

Table of contents

• Cover
• Title page
• Copyright page
• Preface
• Part 1: Magnetic Materials
• Part 2: Optical Materials
• Index
• End User License Agreement