The IEEE Magnetics Society is the premiere organization for professionals in magnetics research and technology.
Worldwide efforts are underway to create revolutionary and energy-efficient data storage technology such as magnetic random-access memory (MRAM). An understanding of spin dynamics in inhomogeneously magnetized systems is indispensable for further development of nanoscale magnetic memory. This lecture provides a clear picture of inhomogeneously magnetized systems, such as magnetic nanowires with domain walls and disks with magnetic vortices, and presents not only technological developments and key achievements but also the unsolved puzzles and challenges that stimulate researchers in the field.
First, the basic concept of an inhomogeneously magnetized system is described by introducing a magnetic vortex structure in a magnetic disk. A magnetic domain wall in a magnetic nanowire is also provided as a typical example. The magnetic field-driven dynamics of these inhomogeneously magnetized systems are described to illustrate their uniqueness. Second, electric-current-induced dynamics of magnetic vortices and domain walls are described. One can flip the core magnetization in a magnetic vortex using electrical current excitation, and move a domain wall by current injection into a wire. The next part focuses on the applications of current-induced magnetization dynamics in devices. The basic operations of two kinds of magnetic memories—magnetic vortex core memory and magnetic domain wall memory—are demonstrated. The lecture describes not only the current understanding about inhomogeneously magnetized systems, but also unexpected features that have emerged. It concludes with prospects for future developments.
Magnetoresistive (MR) devices with low resistance-area product (RA) and high MR ratio are required for read sensors of high density hard disk drives (HDDs), high capacity STT-MARMs and other sensor applications. Here we review our recent activities on structure-property relationships of magnetic tunneling junctions (MTJ) and current-perpendicular-to-plane giant magnetoresistive (CPP-GMR) devices using combinations of new ferromagnetic (FM) and non-magnetic (NM) materials. For FM materials, we explored several Heusler alloys with high spin polarization. For NM materials, we explored new tunnel barriers that have excellent lattice matching with FM electrodes and new spacer materials with good band matching with FM layers. We also explored some oxide and compound semiconductors. To extract the highest MR outputs that can be expected from the intrinsic properties of the FM/NM combinations, optimization of the device structure is essential. Using an aberration corrected STEM, we characterized the interface structures of layered devices with a near-atomic resolution, by which we investigated the underlying mechanism for magnetic and transport properties of the MR devices.
Magnetite, Fe3O4, guided early explorers towards unknown frontiers. Since those days, oxides have been the backbone of many scientific and technological developments. When high temperature superconductors were discovered, the subsequent enthusiasm stimulated an impressive development in oxide thin film growth technologies and a deep revision of the understanding of metal oxides and strongly correlated electronic systems. Today, oxides are fueling the discovery and development of unexpected, intriguing, and fascinating new areas of knowledge, such as magnetic ferroelectrics and magnetic monopoles. Ferromagnetic oxides are finding their way as active components in spintronics, either as spin filters for advantageous magnetic tunnel junctions or used to manipulate spins in non-magnetic materials, which could eventually lead to energy-efficient pure spin-current devices. The tiny spin-orbit coupling interaction, responsible for the magnetic anisotropy, has emerged as a toy that allows us the modulation of the transport properties, not only in metallic ferromagnetic systems, but also in antiferromagnetic metals and insulators. This may lead to a new generation of magnetic memory. “Interface is the device” and interfaces between oxides and metals, and interfaces between large band-gap oxides, have led to the discovery of emerging properties such as switchable “on-off” magnetization, by applying suitable electric fields, or magnetism and superconductivity in confined two-dimensional electron gas systems, which challenge our current understanding of oxides.
This is the playground in which we fortunately play, learn, and imagine the future while enjoying building a new science out of the good old oxides. In the lecture, we will travel through the new materials and ideas that make this journey possible and so successful.
This presentation reviews the motivation, history, and recent progress in nanoscale strain-mediated multiferroics. Research descriptions include analytical and experimental work on strain-mediated multiferroic thin films, single magnetic domain structures, and superparamagnetic particles. The results indicate efficiencies orders of magnitude superior to STT approaches and presents a new approach to control magnetism. Discussions of future research opportunities and novel applications are included.
The recent interest on the magnetization reversal process of novel families of nanowires originates in the need to have full information about their magnetic properties for different functionalization and technological applications. The electrochemical route to fabricate nanowires is attracting much interest owing to their low-cost and reliability to fabricate tailored magnetic nanowires and nanotubes. This technique enables the synthesis of nanowires with cylindrical symmetry in opposition to nanostripes prepared by lithography techniques. Arrays of such nanowires can be grown with diameter of 15 to 200 nm, and length from 100 nm up to tens of microns. Cylindrical nanowires can be also grown with compositional multisegmented character and with controlled modulation in diameter intended to play a similar role as notches in lithography nanostripes. The particular study of Co-based nanowires is relevant since their magnetocrystalline anisotropy, in opposition to Py nanostripes, plays an important role to determine the magnetization reversal mechanism by vortex or transverse domain walls and spin rotation modes.
Most thin magnetic films have their magnetization lying in the plane of the film because of shape anisotropy. In recent years there has been a resurgence of interest in thin magnetic films which exhibit a magnetization easy axis along the surface normal due to so-called Perpendicular Magnetic Anisotropy (PMA). PMA has its origins in the symmetry breaking which occurs at surfaces and interfaces and can be strong enough to dominate the magnetic properties of some material systems. In this talk I explain the physics of such materials and show how the magnetic properties associated with PMA are often very well suited to applications. I show three different examples of real and potential applications of PMA materials: ultralow power STT-MRAM memory devices for green computing, 3-dimensional magnetic logic structures and a novel cancer therapy.